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Table of contents
0. Introduction
Simple chronology
1. The Big Bang ... a fluctuation of vacuum [Inflation]
2. Elementary particle ... E = mc 2 [gauge theory]
3. Formation of atomic nuclei...dark mass and energy [Large-scale structure of the universe]
4. Stars ... Cosmic dawn [Cosmic background radiation]
5. Elements ... Alchemy is synthesis of a nucleus [nuclear energy]
6. Black hole ... Birth and death of stars [Horizon of events]
7. Heavy nucleus ... Even atomic nuclei evolve [half-life]
8. Dark matter ... an imperator of gravity [Neutralino]
9. Virgo Supercluster ... Large-scale structure of the Universe [Voids]
10. Formation of galaxies … stars gathered in gravity wells [starburst]
11. The birth of the Milky Way Galaxy ... headwaters of the Milky Way [globular clusters]
12. The present state of Milky Way Galaxy ... The structure of the microcosmos [binary stars]
13. Solar system ... Order of the sky [heliosphere]
14. Origin of the Solar system ... accretion disc [gravity]
15. the Earth ... Non-gas components of the solar system [chondrules]
16. Moon ... Giant Impact [tidal force]
17. Crater ... heavy bombardment of the Hadean eon [aerosol]
18. Core...Separation of the Earth's interior [Geomagnetic field]
19. The Sea ... Separation of materials on the Earth's surface [Supercritical Fluids]
20. Atmosphere ... cooling of the Earth's surface [water]
21. Plate … crust before tectonics [Convection]
22. Life ... Is it incident or inevitable? [hierarchy]
23. Generation of unit molecules for making life ... The sky, the sea and the sea floor [Frontier molecular orbital theory]
24. The birth of macromolecules for living system … hydrothermal vent [Polymerization]
25. Carbon dioxide assimilation ... Growth of organic matter [Catalyst]
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Simple chronology
The biginning of the Universe 13.798±0.037 billion years ago
History of the big bang（after the big bang）
History of the Earth
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This e-mail magazine was started in 2003. Thinking back to that time, the Internet had accumulated a lot of information, and even AI had been developed to effectively compile knowledge from around the world.
My initial goal was to organize and systematize my thoughts, but now it has become my own compass for living in a world, overflowing with a huge amount of information and opinions. In order to write in a well-rounded way, I have adopted the method of telling history along all timelines that I am aware of (the genealogy of all things in the universe. That is, the big history), and summarizing various ways of thinking (the genealogy of a hundred schools of thought) selecting points from that history. I have tried to use everyday language for my expressions. That said, technical terms are indispensable for conveying knowledge accurately. Fortunately, thanks to the search function of the Internet, even if some technical terms are used, simple explanations can be found quickly in the Internet. Nevertheless, I continue to make efforts to express advanced ideas in everyday written language.
I used e-mail magazines, which was popular at the time, as a tool to create my own opinion, and put them together in my homepage by myself using HTML, but it is now outdated. However, the format is a very good way to continue, one section at a time every week, of explaining the history of the universe, the history of the Earth, the history of life, and the history of humanity, from the birth of the universe to the present day with a modern perspective, to the farthest future. Until now, I have placed emphasis on the genealogy of the universe, but from now on, I would like to write about scientific awareness and life-philosophical understanding. I will move on to the next chapter even if I have not yet digested the content I probably understand, and once I have reached the future chapter, I will write a revised version starting from the Big Bang. By building up in this way, I will be able to thoroughly check my philosophy and basic knowledge as a whole.
We all have large amounts of non-classified knowledge, and we always want to make them systematic. In school days, textbooks would have been a system of knowledge. When becoming a social worker, knowledge gained in daily life is fragmented, such as activities in the workplace, family and community, and professional knowledge on work, personal knowledge reading and hobbies. When fragments of knowledge are connected with unexpected links, or when I notice conceptual similarities between the fragments, my cross-contextual system of knowledge will expand slightly. I feel pleasure at such works. These are the metacognitive or transferable skills.
Over the course of several versions, I began to think that it was assembled into new "myth = creation of the world". The hobby that I enjoy using e-mail magazines is, to make it a big history, the same as creation the world by utilizing the knowledge accumulated through science. As in the doctrine and philosophy of the former religion, this new "myth" needs to overlap as much as possible with every life, and it will be a tool to enrich the life and society as a whole.
Unfortunately, there are some historical blanks in human knowledge. That part was filled with one of hypothesis or my hypothesis that seems plausible for me. I chose the hypothesis based on my confidence that I have solidified philosophy of science. It is a statement that I want to continuously explain the history of the universe with a reasonable hypothesis. This volume does not investigate into the general theory, nor does it introduce a unique view that is different from the traditional one. It is just a compilation of the efforts of the wonderful people introduced in the literature at the end of this volume.
Since this is work for myself only, I have an image like assembling a block puzzle according to the depth of my own recognition, to the extent that I knows. I will quote Mr. Kenzaburo Ohe, Japanese writer with Novel prize. "What I remember incorrectly was much worse than not being memorized was that my father told me, and I respected those who can incorporate in a daily conversation what they remembered from the book, as it is also interesting." (in “To the new people")
About 13.8 billion years ago from now the Universe was born from a fluctuation of vacuum.
The Big Bang theory predicts a singular point in the beginning of the Universe. The size of the Universe at singular point is Planck size (10 -44 seconds, 10 -33 cm). In Planck size, the energy conservation law and Einstein's theory of relativity, and so on, are broken due to Heisenberg's uncertainty principle. In this size, substances are generating and/or disappearing in vacuum (virtual particles).
Immediately after birth, the Universe rapidly expanded due to inflation by 10 -34 seconds, and it became overcooled. The universe became extreme dense at high temperature with the energy released when the vacuum transformed from an unknown state to the Universe of the present state. Since the true nature of its energy is unknown, it was named inflaton, and the space in which the Universe existed was called the inflaton field. It is hypothesized that as the Universe fell from a high point of the energy state of the inflaton field to a low point, the inflaton was converted into inflationary energy and filled the Universe.
On the other hand, inflation can also be explained by Einstein's equations. Gravity has no repulsive force, but only attractive force. However, when the energy packed into an extremely small space with a diameter of 1x10-27 m with uniformity, antigravity can appear. It is speculated that antigravity will explosively stretch the tiny space to the size of the current observable universe in a short time.
The Universe which rapidly expanded by inflation extended the initial small fluctuation as it was. Currently, the fluctuation manifests itself in a slight non-uniformity of cosmic background radiation and unevenness in the distribution of galaxies. Small fluctuations were magnified by gravity, forming a large-scale structure of the Universe. The artificial satellite named Planck for observation of the cosmic background radiation was launched in 2009 and the data were opened in 2013. The composition of the Universe was 4.9% for baryon, 26.8% for dark matter and 68.3% for dark energy. The Hubble constant was 67.15 ± 1.2 km/sec/Mpc, and the age of the Universe was 137.98 ± 0.37 billion years.
It is thought that force (interaction) was born at the same time of the birth of elementary particles. Gravity first emerged from the unified field. It is estimated to be 10-38 seconds after the universe was born. Inferring from other interactions which are transmitted by exchange of elementary particles such as photons or gluons, the putative particle that transmits gravity is called graviton. As gravitational force (universal gravitation) acts all elementary particles, and works to infinity without being interrupted, so it dominates in the stellar world. Gravitational force is responsible for navigation of the celestial bodies such as the Earth, the Sun, the galaxy, and it creates a huge structure in the Universe.
Space inflation began immediately after the birth of gravity, and was completed at 10 -34 seconds after the Universe was born. Then, at 10 -33 seconds, the strong interaction between quarks mediated by gluon and the electroweak interaction (weak interaction and electromagnetic force) appeared. Quarks, leptons (6 species. among them, the electron and the neutrino are stable) and the gluons were in a state of free motion in the Universe at a very high temperature. The plasma of quark and gluon showed behaviors like gas or liquid. At that time, the weight of a mass like a tip of pin was as heavy as that of the Egyptian pyramid, and the temperature reached one million times of the center core of the Sun.
At 10 -13 seconds after the universe was born, along with the cooling of the Universe, the electroweak interaction was divided into weak interaction and electromagnetic force. The weak interaction can transmit very short distance, so we cannot observe their impact in the everyday world. Almost at the same time, at 10 -13 seconds thereafter the vacuum was filled with Higgs particles (Higgs' sea, or Higgs field), masses were created in elementary particles (other than photons) interacting with Higgs particles. Quarks and leptons reacted with the Higgs field. When flying in space, they received brakes by the Higgs field, the speed became lower than the speed of light. Also, when accelerating or changing the direction of particle motion, certain external force needs to be exerted.
Static mass energy does not decrease even if the Universe expands. On the other hand, the wavelength of light became longer as the universe expanded, meaning that the energy contained in light became smaller. Therefore, the energy density of matter decreases by the amount of increase in volume due to the expansion of the Universe, but its rate was slower compared to the decrease of energy density of light. As a result, as the Universe expands, the energy density of matter increases compared to that of light. By the time protons and neutrons were born (10 -6 seconds after the birth of the universe), the energy density of matter was only one billionth of that of light.
A state filled with light, that is, what is called a photon gas, has a high pressure. When the density increases in a certain region, it tries to return to the original density by the repulsion due to the correspondingly increased pressure. Therefore, during the energy density of light is higher, the density fluctuation cannot grow no matter how hard the gravity works.
At 10 -6 seconds after the birth, the quark joined by gluon, protons and neutrons (complex of three quarks) and mesons (pair of two quarks) were born. Protons and neutrons formed atomic nuclei via mesons. The elementary particles responsible for strong interactions, gluon, are trapped in protons, neutrons, and nuclei, and from then on, none can see them in the everyday world. As the temperature further declined, protons and neutrons, their associated nuclei, electrons, photons, and neutrinos were left as basic particles in the Universe at 10 -4 seconds after the birth. At that time, the Universe was filled with dark matter in addition to the elementary particles. The number of nuclei produced was 1 per 1 billion photons.
One minute after the Universe was born, the deuterium atomic nucleus, in which a proton and a neutron are coupled, were stabilized. Then nuclear fusion advanced and light nuclei were synthesized. In the early Universe, almost atomic nuclei were consisted one proton, that is hydrogen (or deuterium, if a large number of neutrons were created) or two protons (helium nuclei).
Neutrons, protons, and electrons combined with photons to form a liquid plasma state, and fluctuations of small density became waves (baryon acoustic oscillations) that filled the Universe. At first, the ratio of protons and neutrons was 1:1, but the neutrons are so unstable to decompose into protons and electrons. This decomposition sharply decreased after 3 minutes post Big Bang, because nuclei started to be formed. At this time, the number of protons became seven times the number of neutrons.
Three minutes after the Big Bang, nuclei of hydrogen and helium were formed. There are three kinds of nuclei of hydrogen including one proton and 0, 1, or 2 neutrons. In addition, atomic nuclei of helium are two kinds including 2 protons and 1 or 2 neutrons. The universe was filled with nuclei and free electrons, which was still plasma state. Furthermore, very few lithium and beryllium nuclei were born in 1000 seconds after the Big Bang.
The energy density of photons drops sharply with the expansion of the Universe. It was 50,000 years after the birth of the Universe that the energy density of photons finally became less than the static mass energy densities of ordinary matter and dark matter. If main source of the energy density of the Universe changed from light to matter, the speed that the Universe expands would also change. There is no change in the gradual deceleration of the expansion rate, but the degree of deceleration became smaller because the decrease in the energy density of the substance was slower than that of light. At the same time, the reversal of the energy densities of matter and light begins to amplify the density fluctuations of the Universe, which is the driving force for the formation of stars and galaxies. The density distribution of matter was generated as a superposition of waves by baryon acoustic oscillations.
Starting with the density fluctuations created by inflation as the initial conditions, the smaller scale fluctuations grew first. Therefore, a small halo was able to be created first, and then it repeatedly coalesced to grow into a larger halo. Eventually, galaxy-scale halos appeared, leading to large-scale structures of galaxy clusters and the universe. And stars are born in the dark matter halo. It is also the birth of a galaxy.
Galaxies are making groups on a scale of about 10 million light years. Galaxy groups and galaxy clusters (larger than group) further form a supercluster. The Milky Way Galaxy which our solar system resides belongs to the Virgo supercluster. Galaxy supercluster has size of several hundred million light years. In the Universe there is a large space where there is no galaxy. Examining the distribution of the galaxy, it turned out to be a foamy structure, and the galaxy turned out to be gathering around bubbles (space without galaxies. so called Void).
Sum of gravity of visible stellar matters is not sufficient to produce the large-scale structure of the Universe. A theoretical calculation shows it takes too much time to form it. Assuming a dark matter with mass of several times larger than one of visible materials, a hypothesis was born that stars and galaxies were formed around dark matter through attracting interstellar gases and stars. The dark matter is indirectly measured its mass and distribution using the gravitational lens effect. When you look at the map showing the large-scale distribution of dark matter in the Universe, you can find the network structure of the dark matter grows with the passage of time (as it approaches the Earth), and it seems to be separated by a huge void. The galaxy formation was demonstrated visually that the galaxies concentrate along the network structure of the dark matter and the galaxies grew in the dark matter.
After inflation, the expansion of space is thought to have gradually slowed down. Recently, it was observed that the far supernova flied away at a speed higher than the speed when considering the expansion rate of the Universe is constant. That is, the expansion of the Universe is accelerating. Therefore, we are newly introducing and explaining the concept of dark energy. Before 13.8 billion light years, space expands at a speed exceeding the speed of light, so it is called the horizon of the Universe. The current universe calculated from the speed of expansion is a radius of 47 billion light-years. The outermost side of the space is an account which is far away at more than three times the speed of light.
There is a theory that interprets dark energy as the cosmological constant of Einstein's equation. In this case, since it is a constant, the density of dark energy in any part of the universe is always constant even if the universe expands. In other words, if there is always a constant amount of dark energy in the space of the universe, the total amount of dark energy will increase as long as the universe expands. This is a strange phenomenon that occurs because dark energy is understood using the normal concept of energy.
When the temperature of the Universe cooled to about 4000 K (K is absolute temperature) after about 380,000 years after the Big Bang, electrons were captured around the nucleus by electromagnetic force, then atoms were formed. This phenomenon is called neutralization of the Universe. Then, the light, which could not go straight by absorbed or released by free electrons, could go unimpeded. Thus, the Universe became transparent (clarification of the Universe). The size of the universe at that time is estimated to be one thousandth of its current size. Radio waves with a wavelength of 21 cm emitted from hydrogen atoms filled the universe. Today, this is observed as the cosmic background radiation with a wavelength of 2.7 K.
The emitted electromagnetic waves were absorbed by hydrogen molecules throughout in the Universe. The hydrogen molecules absorbed the light and emitted light to reach equilibrium. When a star was born, the equilibrium was disrupted by the light emitted by the star. It is thought that this disruption can be detected as the intensity of microwave absorption. Observations have shown that hydrogen molecules were formed 180 to 250 million years after the birth of the universe, and that stars were born after that.
Small primitive stars of about 1% of the solar mass were formed 300 million years after the Big Bang. The primitive stars gathered the gas around, grew and began to shine strongly when it was about 20 times of the solar mass. Their growth was suppressed by light pressure, and growth stopped at about 40 times the solar mass. Another simulation predicts a huge star that will reach 100 times the solar mass. The first stars are called the first generation. They are composed mostly of hydrogen and are much larger, hotter, and emit more photons than stars that contain heavier elements, such as the Sun.
Many first-generation stars appeared to be born 50 million years after the Big Bang. The first generation stars are mostly made of hydrogen, and are larger and hotter than stars that contain heavy elements such as the Sun and emit more photons. In 180 million years after the Big Bang, hydrogen atoms were heated by stellar light, and ionization of the hydrogen atoms began. The first generation stars had a short life span due to its large mass, and supernova explosions frequently occurred.
Hydrogen left in the space ionized by ultraviolet rays from the stars. This process after about 500 million years from the Big Bang is called re-ionization of the Universe. The oldest (furthest) galaxy that can be observed now is a quasar of about 300 million years after the Big Bang (13.5 billion light years ahead). As galaxies formed, hydrogen atoms became scarce in space. Spectroscopic analysis of the light from quasars more than 12 billion light years away estimated that hydrogen atoms would no longer be detectable in space about one billion years after the Big Bang. This is called the dawn of the Universe.
For example, the light emitted from the GN-z11 galaxy 13.4 billion years ago has finally reached the Earth, but the Universe is expanding. If you subtract the expansion, when the light was emitted, the distance to GN-z11 was about 3 billion light years. The Earth did not exist yet. The Universe expanded while the light was traveling, and it took 13.4 billion years to reach the Earth. Currently, the distance between GN-z11 and the Earth has increased to about 31.4 billion light years.
If you go back more than 10 billion years in the past, there is a noticeable increase in peculiar galaxies such as interacting galaxies and starburst galaxies.
The lifetime of a star is called evolution. The mass of the first generation stars that were first born in the Universe are orders of magnitude larger than those of the present age, because the Universe was so small that the high concentrations of hydrogen and helium were available as materials. Hydrogen gas flocculated due to gravity. When the central part of the gas exceeded 10 million degrees, nuclear fusion reaction started.
In the early Universe, the ratio of number of hydrogen with a proton to deuterium containing neutron was estimated to 6:1. Deuterium is generated from two hydrogen nuclei (protons). When two protons collide, one emits a positron and a neutrino and turns into a neutron (Beta plus collapse). Positron annihilates with surrounding an electron and turns into gamma rays. Thus, a deuterium nucleus is formed composed of a proton and a neutron. When a proton, a hydrogen nucleus, is bonded to a deuterium nucleus, a helium 3 nucleus (two protons and one neutron) is formed. Two helium 3 nuclei react with each other to form a helium 4 nucleus (two protons and two neutrons) and two hydrogen nuclei (one proton each).
The helium nucleus accumulated in the core of the first generation star as an ash of the nuclear fusion reaction, and outside the core, hydrogen nuclei continued fusion reaction. Eventually, as hydrogen nuclei become less and nuclear fusion reaction becomes weaker, the temperature dropped. As the temperature decreased, the central core shrank due to gravity, and its temperature and pressure rose. Then helium nuclei began nuclear fusion reaction. Three helium nuclei turned into one carbon nucleus (6 protons). Furthermore, oxygen nucleus (8 protons) was formed from a carbon nucleus and a helium nucleus. Subsequently, carbon underwent a nuclear fusion reaction.
Nuclei such as neon (10 protons), sodium (11 protons), magnesium (12 protons), etc. were formed a nuclear fusion from 2 carbon nuclei. Further nuclear fusion reactions produced silicon (14 protons), Iron (26 protons), and so on.
When the main nuclear fusion reaction ends inside the star, heat was no longer generated, the core of the star shrinks. Then the temperature and pressure of the core rise to start the next nuclear fusion reaction of heavier nuclei. The temperature and pressure of inside of the star gradually become high. As heavier nucleus accumulates in the core, the core of the old star has several layers of nuclei. In the core of large and old star, iron nuclei were accumulated.
As the atomic number increases, nuclear fusion reactions are less likely to occur because the Coulomb repulsion between the nuclei (the force that particles with the same charge repel each other, the nucleus has the positive charge of the proton) becomes large. The heaviest element that can be generated in the nuclear fusion reaction is iron, having an atomic number of 26. That is, nuclei lighter than iron were produced inside the first generation stars.
After the Universe was born, in the hundreds of millions of years, the first generation stars got a supernova explosion and became black holes. The energy of the supernova explosion released relatively light nuclei produced by nuclear fusion reaction into outer space. In addition, heat and pressure of explosion created a heavier nucleus than iron.
The gas temperature dropped when the first-generation star exploded and the heavy nuclei were scattered into the space. The relatively cold gas clouds were broken apart and each became a star. Since then, no huge star nor black hole like the first generation star were not formed.
If only hydrogen and helium are component, the temperature of the gas rises so high during the formation, and only very massive cloud can become a star. First generation stars are considered to be 100-1000 times the mass of the Sun. When the iron core of the first-generation massive star reached to temperature of 5 to 10 billion K, the energy of the emitted light reaches the level of energy connecting neutrons and protons in a nucleus. This high energy light caused nuclear fission. The iron nucleus decomposes into helium nuclei and neutrons, which is an endothermic reaction. As the temperature decreases, the pressure maintaining the core mass sharply drops and the outer layer of the star fall toward the center. The nuclear fusion reaction accelerates at once, the outer layer of the star blows off, and a supernova explosion occurs.
In the case of massive stars, high pressure causes electrons to be absorbed by protons and turn into neutrons. In this phenomenon, called electron capture, the up quarks in protons turn into down quarks, and an electron neutrino is emitted. A star that contains only neutrons is called a neutron star. If the star's mass is even greater, it will not be able to maintain its shape as neutrons, and the neutron core will collapse inward due to the strong gravity. This is called gravitational collapse, and the core will condense into a black hole.
The first generation supernova explosion blew out the surrounding gas by gravity wave. The compressed interstellar gas created a number of second generation stars. Even small amounts of heavy elements scattered around during a supernova explosion have a significant impact on the formation and structure of stars. Heavy elements emit more infrared light than hydrogen and helium. When heavy elements are present, a relatively small amount of gas can contract into a star. Heavy elements act as a coolant when stars are formed, suppressing expansion due to heat. From the second generation onwards, relatively lightweight stars began to be born.
Stars of the second generation have a long lifetime because the mass is small compared to the first generation. The second generation stars are currently observed in clusters around the galaxy as a star with poor metal element. When a massive star among the second generation reached the end of a supernova explosion, a large number of heavy nuclei were supplied to the universe. The stellar made after this contains a relatively large number of metallic elements and is called a third generation star. The Sun is the third generation. The galaxies of 10 billion years ago have been confirmed that their interstellar gas contain very low heavy elements. In the galaxies of the same age, it is also observed only small number of galaxies storing large amounts of dust and heavy elements.
In supernova explosion, a large number of neutrons are generated. Neutron has no charge. Coulomb repulsive force does not work so that neutrons are easily absorbed with the surrounding nuclei. A nucleus containing more neutrons than usual becomes unstable, so an excess neutron releases electron and gamma ray to become a proton, hence increases the atomic number by one. With this repetition, a large number of heavy nuclei more than iron were created in a short time. Although this is usually the description in textbooks, it is difficult to synthesize heavy atomic nuclei. Here is a summary of the knowledge available so far.
Until now, element synthesis has occurred through the Big Bang and nuclear fusion reactions inside stars. The Big Bang produced large amounts of hydrogen and helium, including trace amounts of lithium. Since stars were born, nuclear fusion reactions produced nonmetallic atomic nuclei such as carbon and nitrogen, as well as elements ranging from helium to iron (atomic weight 26). Furthermore, in the cores of old red giants, neutron-rich conditions continued for a long time, which led to the formation of atomic nuclei heavier than iron. It is believed that elements ranging from strontium (atomic weight 38) to bismuth (atomic weight 81) were formed.
Not all nuclides are born in supernova explosions. In normal gravitational collapse supernova explosions, rubidium (atomic weight 37) is formed from light nuclides such as oxygen, sodium, chlorine, and carbon. In double star systems known as Type Ia supernova explosions, where stars periodically undergo supernova explosions due to fallout from a companion star, calcium, sulfur, nickel (atomic weight 28), copper (atomic weight 29), and other elements are born. In particular, Type Ia supernova explosions from neutron stars, known as X-ray bursts, produce strontium (atomic weight 32), rubidium (atomic weight 37), molybdenum (atomic weight 42), and other nuclides. The following nuclides are heavier than iron (atomic weight 26).
The phenomenon thought to produce the heaviest elements is the collision and merging of neutron stars, which produces platinum (atomic weight 78), gold (atomic weight 79), and uranium (atomic weight 92). This is just a guess, but it is possible that when a black hole is directly formed in a supernova explosion, the outer core of neutrons is blown off just before the black hole is formed, creating a heavy atomic nucleus.
The dark matter that filled the early Universe had density fluctuations of about one in 100,000, and these fluctuations grew due to gravity and gathered baryons. The dark matter aggregates surround galaxies as spherical halos. After the atoms were formed, the gravity wells of the dark matter collected hydrogen and helium atoms. The hydrogen and helium gas bodies further condensed due to gravity and formed stars. When the stars reached the end of their lives and exploded as supernovae, the shock waves condensed the surrounding gas clouds, and even more stars were born. The newborn stars fell into the gravity wells created by the dark matter and gathered together, forming several galaxies. The galaxies formed within the dark matter became disk-shaped due to their rotation.
In the center of a large galaxy in the Universe, there is a black hole with a mass between 1 million and 1 billion times of the solar mass. The black hole at the center of the galaxy is thought to have been formed by the gravitational collapse of a huge gas cloud during 1 billion years after the Big Bang. An ancient massive black hole is observed as a quasar. A quasar is a celestial body where powerful electromagnetic waves are generated due to a large amount of substances falling into a huge black hole. Iron was found from the spectroscopic observation of a quasar.
Eventually, the first generation of stars exploded as supernovae, scattering heavy atomic nuclei, lowering the temperature of the gas, and the relatively cool gas cloud broke into smaller pieces, each of which became a star. After that, small black holes were formed when stars with a mass about 10 times that of the Sun collapsed due to gravity during the supernova explosion.
In the early universe, which is only 2 billion years after the Big Bang, we can find many massive gas bodies with masses that are almost the same as galaxies. Giant gas bodies create numerous stars and would condense into galaxies. Recent observations in the young universe of 4 billion years after the Big Bang suggest that star formation activity was at its peak in large mass galaxies. Stars were born there with an unexpectedly high formation rate.
In the universe up to two billion years after birth, glowing lumps of hydrogen gas of galaxy size are observed. They are called Lyman-alpha blobs (LABs). Having a black hole in the center, it looks shiny by the substance falling into the black hole. The size of LABs is almost the same size of the current galaxy. It is thought that LABs evolved into galaxies. Unless LABs are assumed for the evolution of the Universe, the size of the modern galaxy would be enormous in size. It is thought that the formation of the second generation star in LABs was completed by from 3 to 4 billion years after the Universe was born.
The star formation rate of the galaxy is correlated to the total mass of the material which makes the star. From the beginning of the universe to the present, the star formation rate has gradually decreased. Even in early galaxies of the Universe, the star formation rate increased with the mass of the galaxy, and its efficiency was more than 20 times higher than it is now. The black hole located in the center of the galaxy is called blazar. Study examining the gamma-ray attenuation from blazars in the range of 200 million light years to 11.6 billion light years shows that the gamma ray was the weakest between 9.7 and 10.7 billion light years, indicating that many stars were born in this time period. The amount is 10 times of the current. In other words, after the Big Bang, there was a peak of star birth 3 to 4 billion years later.
The mass of black holes at the center of galaxies, including medium-sized black holes, is correlated with the size of the galaxy. Therefore, one possible scenario is that black holes grow by merging with other galaxies through collisions or by absorbing surrounding stars. The influence of dark matter in this process is considered.
The results of an international project to observe the distance and recession of distant galaxies using Type Ia supernovae in the 1990s have revealed that the Universe has been expanding since its birth. Initially, the expansion rate is gradually slowing down. The gravitational force of the mass of the Universe braked the expansion of the space, resulting in deceleration expansion. However, from 7 billion years ago, the universe changed from decelerating expansion to accelerating expansion. Dark energy is supposed to be the source of the accelerating energy.
The mass distribution in the present Universe has a bubble-like structure, reflecting the fluctuation of density in the early Universe. That is, galaxies are found gathering around a huge space (void) where no galaxy exists. The collective state of galaxies is named as a galaxy group, a cluster of galaxies, or a supercluster.
The solar system belongs to the Milky Way galaxy. the Milky Way galaxy belongs to the Local Group of Galaxy. In the Local Group of Galaxy, the largest galaxy is the Andromeda galaxy, and the heaviest galaxy is the Milky Way galaxy. There are many companion galaxies are bound by their gravity around both galaxies. It contains about 50 dwarf galaxies in the range of 10 million light-years. The Milky Way is theoretically believed to contain 220 dwarf galaxies, but recent observations suggest that it may contain as many as 500.
One of the groups of galaxies that are closest to the Local Group of Galaxy is the Sculpture Room Group of Galaxy and the Maffei Group of Galaxy, which are separated by 7-10 million light-years. In addition, the Ursa Major M81 Group of galaxy, M101 Group of Galaxy, Aquarius M51 Group of Galaxy, Centaur A / M83 Group of Galaxy.
There is a Virgo galaxy cluster about 50 million-70 million light years away, all of which are included in the Virgo super galaxy cluster. The Virgo Cluster contains 1300 to 2000 galaxies, 15 million light-years across, and has a huge elliptical galaxy called the M87 galaxy in the center. The supermassive black hole in the center of the M87 galaxy was photographed in 2019. All of these are included in the Virgo Supercluster.
Although some astronomers think that the Local Group of Galaxy is absorbed into the Virgo Galaxy Group, there is a negative opinion because the expansion of the Universe is faster, which accelerated by the dark energy. Recently, a huge attractor has been discovered that is attracting the surrounding galaxies about 200 million light years. It is proposed as La Keania superclusters, including the Virgo cluster and local galaxies.
A huge hole was discovered in the Ophiuchus cluster of galaxies, 390 million light-years from the Earth. It is estimated to be 15 times larger in diameter than the Milky Way. It is assumed as the trace of a huge explosion. The Ophiuchus cluster of galaxies is consisting of thousands of galaxies. At the center of the Ophiuchus cluster, there is a galaxy with a huge black hole with a mass of 10 million times of the Sun. It is hypothesized that a jet emitted vertically from the black hole intensified for unknown reason and blew away the galaxy beyond it. Not only the density fluctuations of the early Universe but also other factors were possibly involved in the formation of the large-scale structure of the Universe.
Assuming the maximum estimate of total mass of the dark matter, it cannot fill up the gap speed difference between speed of the clustering of galaxies and the expansions of the Universe. Therefore, according to the expansion of the Universe, the space between each cluster of galaxies and super galaxies increases. Ultimately, it is predicted that individual clusters of galaxies are blocked by the wall of light velocity (separation speed exceeds light speed) and separated as an isolated universe (space).
Regarding the appearance of the Universe in the distant future, the conclusion whether it will be a small universe by a cluster of galaxies, that is, a universe that will continue to expand forever, or a big crunch will be depended in the Grand Unified Theory which we have to wait for theoretical analysis.
A large amount of hydrogen gas equivalent to the weight of a galaxy was collected in the gravity well formed by Black Matter, and star formation began. It was a billion years after the Big Bang. The giant star formed in the center of the gravity well burned out in about 10 million years, causing a supernova explosion and scattering a large number of heavy nuclei and its own debris around it. A huge black hole was left in the center.
Supernova explosions promoted the birth of stars. When a large-mass star is born in the center of a huge molecular cloud, the light from a large-mass star exerts pressure on or ionizes the surrounding molecular cloud to create a high-concentration molecular cloud. These molecular clouds condense into stars, and light reaches farther. By repeating this process, a characteristic OB association was formed. In the early days of galaxy formation, it seems that there were hundreds of structures, in which thousands of stars were strongly connected by gravity, such as small satellite galaxies and globular clusters.
Second-generation stars contained a large amount of heavy elements, so they were able to dissipate their heat efficiently, be formed neatly, and shine longer. Second-generation stars exploded one after another 2 to 6 billion years after the Big Bang (12 to 8 billion years ago), increasing mass of heavy atoms in the Universe. Substances that do not emit light by themselves are classified into diffused nebulae, planetary nebulae, dark nebulae, etc. depending on how they look. They are mainly gas and dust. It is called interstellar gas when it has a density 100 times higher than that of normal outer space. Eventually, it is compressed by its own gravity and nuclear fusion begins, and a star is born. In this way, the stars moved to the third generation.
By examining the attenuation of gamma rays from blazars in the range of 200 million to 11.6 billion light years, it was found that the birth of stars was most abundant between 9.7 and 10.7 billion light years, and that the amount was 10 times that of today. This indicates that the peak of star birth occurred 3 to 4 billion years after the Big Bang.
There are dozens of dwarf galaxies around the Milky Way, which are thought to have gathered together during the formation of the galaxy but have not yet been absorbed. There are many old stars, and measurements have shown that there are fewer heavy atomic nuclei (carbon and oxygen) produced by nuclear fusion than in the Milky Way. In other words, in the early stages of the formation of the galaxy, there are thought to have been hundreds of structures, such as small satellite galaxies and globular clusters, in which thousands of stars are strongly bound by gravity.
Since the mass of the black hole at the center of a galaxy is correlated with the size of the galaxy, it is thought that black holes would grow by merging with other galaxies through collisions and absorbing surrounding stars. In addition, when dwarf galaxies merge or are absorbed, the gas inside the galaxy is greatly disturbed, causing starbursts in which massive stars are born one after another, and the galaxy grows.
When the Milky Way and Andromeda galaxies merge in the distant future, gas equivalent to thousands of times the mass of the Sun will turn into stars over the course of millions of years. Because these stars are so massive, they will explode in supernovae one after another. It is predicted that the gas in the newborn galaxy will be blown away by the supernova explosions, resulting in a massive galaxy without no star formation anymore.
There is a region called a halo that spherically surrounds the Milky Way galaxy outside the disk part. The radius of the dark matter halo is about 300,000 light-years, accounting for 90% of the total mass of the galaxy. The oldest celestial bodies among the stars forming the Milky Way galaxy are globular clusters scattered in this area.
One of them is the globular cluster Palomar 5, which is 65,000 light-years away from the Earth. Its age was estimated to be 11.5 billion years. Palomar 5 has elongated bands of stars that are thought to have been stretched by interactions with other dwarf galaxies. These stars are second-generation stars that contain heavy elements such as iron only about a few hundredths of the Sun. The 11.7 magnitude star of the Cetus has only one-eighth of the Sun's abundance ratio, but it was unusual to detect thorium 232 and uranium 238 of radioactive atoms. Based on their relative abundance ratios etc., its age was determined to be 12.5 billion ± 3.3 billion years. This value is considered to correspond to the age of the Milky Way Galaxy.
The Milky Way galaxy was formed by attracting stars around Sagittarius A, the first supermassive black hole. During 13 billion years of its history of the Milky Way galaxy, at least half a dozen incidents that it swallowed small satellite galaxies and globular clusters. The smaller galaxies born in the Milky Way Dark Matter were absorbed by the Milky Way Galaxy one after another.
One of them was the dwarf galaxy Enceladus, which was estimated to have been absorbed 10 billion years ago. The size of Enceladus is thought to be about the same as the Large Magellanic Cloud, which is the current satellite galaxy. Every time the Milky Way galaxy swallowed the smaller galaxy, intense star formation occurred. The growth of the Milky Way galaxy was at its peak 3 billion years after the Big Bang (11 billion years ago). This corresponds to the time when a large number of stars were born in the Universe.
The Milky Way galaxy rotated around the Sagittarius A giant black hole and gradually flattened. Also, a swirl pattern was formed. The spiral pattern of the galaxy is a compressional wave of stars. It happens that gravitational pockets are formed in high density places and it takes time for stars to pass there. In other words, because the stars were rotating motion and accumulated, they became an arm structure. In addition, the interstellar gas also gathered and became a place where stars can be born.
The Milky Way Galaxy is a group of celestrial bodies to which our solar system belongs. Twenty small galaxies (dwarf galaxies) such as the Magellanic Cloud are moving around the Milky Way galaxy, bound by the gravity of the galaxy. The dwarf galaxies are distributed around the Milky Way galaxy within a radius of about 400,000 light-years. A microcosm containing globular clusters, open clusters and other groups of stars and interstellar gas. Most of the stars are in the disk of 100,000 light-years in diameter, and stars in the bulge are older than those in the spiral arm.
At the center of the Milky Way Galaxy, there is a strong radio source, a huge black hole called "Sagittarius A". Since the interstellar matter is concentrated at high density around it, it cannot be seen optically. Observations were made to track the movement of the star existing near the center of the Milky Way Galaxy from the 1990s for more than 10 years. Analysis of the trajectories by the universal law of gravitation revealed that the mass of the giant black hole at the center of the Milky Way Galaxy is 3.7 million times that of the Sun. The diameter is 0.15 astronomical units (22.5 million km).
The jet spewing out from the massive black hole at the center of the galaxy can reach up to several million light years in extent. Although the Milky Way's black hole is relatively docile, bubbles of high-energy particles extend above and below the center for tens of thousands of light years, and it is thought that the black hole was temporarily active in the past (when a large number of stars fell into the black hole).
The disks are occupied by dark nebulae and stars belonging to population I (third generation) such as main-sequence stars and cepheus type variable stars. The red dwarfs are expected to be the most abundant stars to form the galaxies. Their size is less than 1/3 of the diameter of the Sun, the surface temperature is a dark star of about 3500 degrees. The fusion rate of hydrogen is slow, and the lifetime is very long. There is nothing visible to the naked eye. 348 celestial bodies within 10 parsecs (33 light years) from the Sun were examined, of which 239 (about 69 percent) were red dwarfs. Also, half of the stars are binary stars.
In the Milky Way, dust gathers on the galactic plane and actively produces stars. The Sun orbits a little above the galactic plane, moving up and down.
The solar system lies in the plane of the Milky Way Galaxy and is on the galaxy center side of the Orion arm, which is sandwiched between the Sagittarius arm and the Perseus arm. It locates 26 thousand light years from the center of the galaxy. The 6 million stars around the Sun are distributed in a snail-like spiral. The age of the Sun is calculated to be 4.6 billion years from the measurement of the collapse of uranium 238. That is, 9.1 billion years after the universe was born, 7.9 billion years after the Milky Way Galaxy was born. The intrinsic velocity of the sun is 220 km/sec. The sun goes round the center of the Milky Way Galaxy once in 200 million years. It is estimated 23 laps already.
Meanwhile, stars in the Milky Way galaxy in the same position as the solar system rotate at 210 km/sec. The time interval for the solar system to pass through the four arms of the Milky Way galaxy is about 200 million years. After passing one arm, it takes about 200 million years for the solar system to catch up with the next arm. The arms of the Milky Way are a collection of stars and interstellar material. When the solar system passes through them, the Oort cloud is disturbed, and many comets are generated. There is a hypothesis that when these comets fall to the Earth, they break through the crust and cause intense volcanic activity. Earth's past volcanic activity has been active in cycles of about 200 million years.
The Sun is in the middle of a local bubble about 300 light-years in diameter. A thick layer of interplanetary dust is formed around the local bubble, and the interplanetary dust is thinner in the local bubble than the surrounding area. The local bubble is filled with plasma, which has a higher temperature than the surroundings. Furthermore, seven stellar groups are formed on the surface of the bubble, and all the stars are about several million years old. From the motion of the stellar groups, it was predicted that the local bubble was formed by 15 supernovae exploding in 4 times with about every 4 million years interval, from 14 million years ago. It was calculated that the Sun was about 1000 light-years away at the beginning and entered the local bubble 5 million years ago. The Sun will break out of the local bubble in 8 million years.
The elements existing in the solar system are, in increasing order, hydrogen, helium, oxygen, carbon, nitrogen, iron, magnesium, sulfur, aluminum, sodium, calcium, nickel. Most of the substance (mass) is in the Sun. These elements are the nuclei formed by the nuclear fusion reaction inside the stars. Many kinds of heavy atoms produced by supernova explosion or merger of neutron stars were also included.
The main celestial bodies of the solar system consist of the single star, the Sun, eight planets, and satellites orbiting the planets. Planetesimals that could not grow into large planets between Mars and Jupiter remained as asteroids and became an asteroid belt. Just under 120,000 asteroids have been discovered, for example, Ceres, Pallas, Juno and Vesta. The asteroid Vesta has a layered inner structure like the Earth.
Only some planetesimals grew selectively and became protoplanets. They grew and grew by collecting a lot of small planetesimals remaining in the surroundings. When the activity of the Sun rose, solar wind was generated. The wind blew the gas out of the area close to the Sun. At last, the protoplanets collected all surrounding planetesimals. The planets ceased to grow and were born with hard ground like the earth.
On the outside of Neptune, there are many celestial bodies without gas, called Edgeworth/Kuiper belt. The origin of a short cycle comet is here with a cycle of 200 years or less. These objects are collectively referred to as dwarf planets. Pluto, which was classified as planet before, became to be regarded as a dwarf planet.
The Sun releases supersonic plasma called solar wind in every direction, and it creates a huge spheroid cavity in the interstellar gas. This cavity is called the heliosphere and spreads over about 100 to 150 astronomical units (AU) (1 AU is the average distance from the earth to the sun, about 150 million km). The supersonic solar wind decreases rapidly at the surface of termination shock, and then equilibrated at the surface called the heliopause. Outside the terminal shock wave surface, the solar wind flows at low speed and is called Helio Sheath. In this area, the interaction between the solar plasma and the interstellar gas becomes dominant.
By examining the age of the meteorite, it is calculated that the solar system was born 4.6 billion years ago. There is a theory that the birth of the solar system was triggered by a starburst that occurred when a dwarf galaxy collided with the milky way galaxy 4,567 million years ago.
Clouds of interstellar matter that became the solar system was gradually condensed and falling into the center of gravity. Most of the gas was such as hydrogen molecules and carbon monoxide molecules. Although the ratio to the total mass was small, there was also a large amount of minute solid particles of about several micrometers. The gas swirled because the angular momentum was preserved while falling and condensing. When agglomerating due to gravity, gravity and centrifugal force antagonize in a plane perpendicular to the rotation axis of the disc, and the material does not immediately fall to the center. On the other hand, since the centrifugal force does not act in the direction parallel to the rotation axis of the disc, aggregation by gravity proceeds. As a result, the material distribution gradually flattened and a rotating accretion disc was formed.
Then a giant gas ball was made at the center of the rotating accretion disc. The core of the gas ball was compressed and its temperature rose. When its temperature exceeds the critical, nuclear fusion of the hydrogen nucleus started and became the primitive Sun.
In the primordial solar system, it is estimated to be 10 to 100 million years from the time when molecular clouds begin to shrink to the time when the solar system is formed. The dust materials in the accretion disc gathered slowly, making small lumps due to adhesion and inelastic collisions. The small lumps are called pebbles. These pebbles became a planetesimal with a diameter of roughly 10 km. The planetesimals grew while revolving around the Sun, striking each other, stuck together, being broken by the impact of the collision. Some planetesimals had a core of metallic iron. From the accretion disc to the formation of a planetesimals with a diameter of about 10 km was quite quick, estimated to be around 100,000 years. The planetesimals were assembled over the 30-40 million years to form the Earth.
When the mass of the protoplanet exceeds about 10 times the mass of the Earth, the planet can effectively collect hydrogen gas by gravity. Because of the mass of gas component was as many as 100 times that of the solid component in the protoplanetary disk, the mass of such a big planet rapidly increased. Jupiter type planets which had a mass of 10 times of the Earth mass were formed, wearing gas of many times the mass of the core around the nucleus (core). Jupiter was short of weight to switch on nuclear fusion. Similar gaseous gigantic planets were born outer than Jupiter, named Saturn, Uranus, and Neptune. Metallic elements are fewer at the outer side of the solar system, and are considered to be composed of light elements such as ice and dirt.
On the outside of the solar system, the planet formation like the early solar system still proceeds slowly. As the primitive molecular clouds evaporated, these objects appear to have been left behind on planet formation. Eight planets are known in the solar system. There is a theory that there is a ninth planet from the orbit of the dwarf planet outside of Neptune, which is about 5-10 times the mass of the Earth.
The rocks on the Kuiper belt are disturbed by the gravity of Neptune and others, and become comets. By the same mechanism, rocks and celestial bodies are injected from the Kuiper belt into the asteroid belt inside Jupiter's orbit. Kuiper belt objects approaching the Sun lose their volatile components by heat, turning them into ordinary rocky meteorites. In addition, the fall of this rock to the gravity well of the Sun is still ongoing.
The Earth that had orbited around 150 million kilometers from the primitive Sun has a different appearance from other planets.
Constituents of the primitive Earth are estimated by investigating planetesimals that are not absorbed by the planet, drifting in the current solar system. Specifically, they are a meteorite and a comet. Among the meteorites, the oldest one is carbonaceous chondrites that existed since the planet was formed. The chemical composition of this meteorite is the same as that of the solar system except for hydrogen and helium. Besides iron and nickel, it contains a considerable amount of water and hydrocarbons. It includes small spherical particles called chondrule, which is said to have formed 4.56 billion years ago. In the state of zero gravity, volatile molecules will assemble to become spheres. Carbonaceous chondrites are thought to be meteorites that are not subjected to thermal transformation such as melting and solidification.
In the current solar system, the long tail of a comet will additionally contain water vapor around the Earth's orbit. However, at the time when the Earth was born, the energy radiation from the Sun was less than present. The temperature around the Earth's orbit is much lower, and the planet may have contained a lot of ice and organic matter of low molecular weight. The surface of the ancient Earth may have been a mud containing a large amount of simple carbon compounds rather than rocks.
The protoplanet grew by attracting many remaining pebbles and planetesimals around it. When the activity of the sun became active, a solar wind was generated, blowing gas from the area near the sun. In about a million years, a slight difference in size grew into more than a dozen primitive Earths. At that time, Jupiter finally grew up, affecting the orbit of the proto-Earth and pushing the proto-Earth group to the final growth.
The planetesimals falling to the Earth melt due to collision energy, and water and gaseous components contained in them evaporated rapidly. When the Earth became about half the size of the present, gravity reached a strength not to let gas escape, and a layer of the atmosphere was formed. Furthermore, volatile substances were supplied to the Earth from the meteorites fallen to the Earth. The atmosphere and the sea were born 4.37 billion to 4.2 billion years ago. The greenhouse effect of the primitive atmosphere slowed the rate at which heat escapes to outer space. The surface of the Earth gradually turned into magma. Eventually, the surface changed to a boiling magma ocean, its depth reached 500 km, and its temperature reached over 1,000 degrees Celsius. In the magma ocean, heavy iron and other heavy components separated from light rocks and accumulated at the bottom of the magma ocean. However, there are negative opinions on the existence of the Earth's atmosphere before the giant impact.
When the Earth reached to a size with radius of about 70% of the current, the heavy metal accumulated at the bottom of the magma ocean fell to the center at once and made a nucleus. At the same time, the gravity energy released from heavy metal melt the Earth completely. The light rock components, which were the equivalent with magma ocean, were separated from the metal nucleus. As the Earth released heat and cooled, the Earth's overall entropy decreased. As a result, the Earth gradually became organized into a more complex structure.
At the final stage of the formation of the Earth, a protoplanet (called Theia) collided with the Earth, which has about 10-15% of the mass of the Earth (similar size as the Mars). As a result, the last 10% mass was added to the Earth, but the surface layer of the Theia and the Earth splashed around the Earth (Giant Impact). The materials which revolved around the Earth gathered again to form the Moon as an independent celestial body. It was 4.53 billion years ago deduced from the age of the moon rock. The birth of the moon is believed to have occurred around 60 million years after the birth of the sun, based on dating of zircons contained in lunar rocks brought back by the Apollo missions.
The Giant Impact is believed to have been caused by disturbances from giant planets such as Jupiter. It changed Thea's orbit to one that would collide with the Earth. Protoplanets formed in the accretion disk should have rotated in the same direction at the same speed. The Thea is likely a protoplanet that is a sibling of the Earth. The Earth and the Thea orbited in circular orbits at different distances from the Sun, at slightly different speeds, and were drawn closer by each other's gravity. It seems more likely that they merged rather than collided. Before merging, they orbited each other's centers of gravity, and an exchange of material in the mantle occurred. Thea, which had lost part of its mantle and core, remained in the Earth's gravity well as the Moon.
According to a simulation, when a collision occurred on the primordial Earth covered with magma ocean, the magma blew out as a jet, which became a disk in the Earth's orbit and eventually formed the moon. At this time, after the collision, the material of the Thea and the material of the magma ocean scattered around the Earth. The Thea's material immediately collided with the Earth again. On the other hand, the Earth's magma ocean component remained in orbit, so the moon contained 70% of the Earth-derived component. It can be explained that the isotopic ratio is the same between the moon and the Earth's crust. If the magma ocean cooled and hardened smoothly, the precious metal should only be found in the core. The presence of them on the surface of the Earth is explained by the giant impact.
A part of the Thea's iron core and other materials were melted and covered the Earth like a cloud. The metallic vapor as a storm took oxygen atoms from water molecules and the remaining hydrogen covered the Earth as a thick atmosphere for about 200 million years. On the Earth immediately after the magma ocean solidified, rocks covered the surface of the Earth, and carbon dioxide, nitrogen and sulfur dioxide erupted from the Earth. When a hydrogen blanket was applied in this state, organic compounds with a low molecular weight were synthesized.
Examining the samples brought back by the Apollo project, the surface of the moon is entirely made of igneous rock. The white areas are old-fashioned and are members of the granite family (anorthosite, a rock containing many feldspars). The dark areas were made of basalt about 3.5 to 3 billion years ago. After that, there would be no magma activity in the moon. From the seismic wave meter installed in the Apollo project and the deformation measurement caused by the tidal force with the lunar orbiting satellite Kaguya, the moon has a core with a radius of 300 km, a mantle with a radius of 1400 km, and a crust of about 10 km.
The Sun was born 4.57 billion years ago. When Uranus and Neptune were formed about 4.1 billion years ago, the orbits of Jupiter and Saturn shifted, which is thought to have affected the orbits of asteroids as well. Early in the formation of the solar system, Jupiter moved to an orbit closer to the Sun, while Saturn, Uranus, and Neptune were pushed outward. As a result, dwarf planets formed outside Neptune's orbit were destroyed and became the Kuiper belt, and they also began to form elliptical orbits like Pluto. They also bundled asteroids into their current positions and sent a large number of meteorites into the center of the solar system.
Observation of the moon craters estimates that most of the craters were made intensively about 4.1 billion years ago by impacts of asteroids in the orbit between Mars and Jupiter deduced from the size distribution. Approximately 4.1 billion years ago, asteroids have fallen as meteors to the Earth during from tens to hundreds of millions of years and is called the late heavy bombardment. Since they were meteorites from the outside of the snow line, a large amount of water and carbon compounds were supplied to the Earth at this time. The depth of the sea of the primitive Earth is estimated to be approximately 2000 meters. The surface of the Earth was almost covered with the ocean. There was a basaltic crust below the sea and a thick atmosphere above the sea.
The number of meteorites that fell to the Earth during the late heavy bombardment period is estimated to be 22,000. Craters with size of 2000 km were estimated to 40, and those of 5000 km were expected to be several. These gigantic meteorites had several hundred kilometers in diameter, completely dried up the sea, broke through the crust and disturbed the upper part of the mantle. The rock temporarily melts, the substance in the mantle was pumped up to the surface, and the substance on the crust was embedded in the mantle. The collision of the meteorite caused the sea and lava to splash into the atmosphere, producing a large amount of aerosol, and mixed with the atmosphere. The sea recovered safely even after the gigantic meteorite collision. Lava was cooled by the sea, and brought various substances to the sea. The basaltic crust revived by rapid cooling of the lava.
When a celestial object collides with the crust, a large amount of crash debris called ejector is generated. Among the ejectors, particularly fine ones are susceptible to chemical weathering reaction because of their large surface area. A large amount of ejector was generated by frequent collision of the heavenly bodies, as a result, carbon dioxide (carbonate ion) dissolved in the sea precipitated as carbonate. Therefore, carbon dioxide in the atmosphere gradually declined.
Impact experiments on small meteorites have shown that meteorites become powdered at the surface of the sea. At that time, organic matter may have been free from decomposition by impact heat. In addition, the fine meteorites may have reached the terminal velocity with the atmosphere as a cushion, and was continuously deposited in the sea. If a large amount of fine meteorites remained after the formation of the Earth, it is possible that the organic matter was supplied on the Earth.
The oldest rock existing is 4 billion years ago (exactly 4,030 million years ago). Rocks made after 3.8 billion years ago can be found in many places. Sedimentary rocks are also found. From these results, it seems that rocks have been preserved stably since 3.8 billion years ago. The sea seems to have stabilized since 3.8 billion years ago after the end of the late heavy bombardment period.
The magma ocean after the giant impact was as deep as the present mantle. It took several million years for the surface to cool and solidify. On the other hand, it took 100 million years for Venus to cool and solidify because of its closeness to the Sun. As a result, Venus lost its water. There would have been no seas.
At that time, the Sun emitted only about 70% of the current energy. At that time, the Earth would not have frozen because it had stored heat from the magma ocean inside and had a layer of atmosphere mainly composed of carbon dioxide. When the magma ocean cooled, komatiite, which has a high melting point, precipitated on the surface. It is thought that komatiite was the first crust of the Earth. Like olivine, komatiite has little silicon dioxide and is rich in iron and magnesium. When experiments are conducted to solidify the magma ocean under high temperature and pressure, bridgmanite precipitates. Bridgmanite is a hard mineral composed mainly of MgSiO3 and has low fluidity. It is likely that bridgmanite accumulated in the lower mantle and restricted mantle convection.
The surface of the Earth melted rapidly due to the meteorites that fell during the Late Heavy Bombardment. The oceans would have completely evaporated several times. The Late Heavy Bombardment lasted 300 million years, from 4.1 to 3.8 billion years ago, so even if a giant meteorite fell, it would have been a short period of time for the destruction of the Earth's crust and oceans.
The early meteorites that formed the Earth were enstatite chondrites, rocks with low volatile content. Because the Earth was inside the snowline at the time, the volatile components around were blown out of the solar system as gas by the solar wind.
Both comets and asteroids were possible as small objects that supplied water to the ancient Earth. In the past, the comet would have supplied water to the Earth. Comets have a main component of ice with dusts around the icy core. On Halley's comet, 80% is ice. However, when the Rosetta space probe surveyed the components of the Gerasimenco comet in 2014, it was found that the hydrogen isotope ratio was significantly different from that of the Earth's sea. At present, the asteroid is thought to be a dominant water source.
During the early magma ocean period, the Earth was completely melted by a giant impact, and then reheated during the heavy bombardment period, causing the heavy elements of the Earth's interior to sink to the center of the Earth and form a core composed mainly of iron and nickel. The Hadean core was liquid metal, and due to the influence of the Earth's rotation, flows were created and formed a magnetic field.
If there was no magnetic field when the Earth was formed, the volatile components would have been broken down by particle rays from space, and the oceans would have dried up quickly. Water vapor is broken down by the solar wind in the upper atmosphere, stripping away the hydrogen. This promotes the evaporation of water vapor, and eventually the oceans disappear.
The current core is formed from a solid inner core and a liquid outer core, and the outer core moves in a spiral motion parallel to the Earth's rotation axis as it convects to avoid the inner core. Just as electric current flows through metal that rotates in a magnetic field, electric current also flows through the liquid metal in the core, creating magnetic field lines according to the right-hand rule.
The Earth's magnetic field reverses at intervals of tens of thousands to hundreds of thousands of years. When this happens, the magnetic field weakens, and cosmic rays and solar wind bombard the Earth's surface for several thousand years. It is believed that terrestrial organisms have been exposed to such dangers many times in the past, but no mass extinctions have occurred. The last time the magnetic field reversed was 770,000 years ago.
When there was a magma ocean on the surface of the Earth, the water in the atmosphere was in a supercritical state. As the temperature dropped below the critical temperature, the water turned into liquid. The Late Heavy Bombardment Period began about 4.1 billion years ago. Meteorites were carbonaceous chondrites and are thought to have had a high volatile content. The Late Heavy Bombardment Period brought water to Earth and expanded the oceans. The sea probably existed 4.3 billion years ago. The sea evaporated several times due to the fall of giant meteorites during the Late Heavy Bombardment Period, but after a while, the sea returned to normal with increased water. They stabilized when the meteorite fall ended 3.8 billion years ago.
At first, water turned to rain at high in the sky where the atmospheric pressure (atm) and temperature were low, but evaporated before it reached the surface of the Earth. As the atmosphere cooled down, the rain gradually reached a low position. Steam becomes liquid water when it becomes at 100 atm and 650 K (380 C) or less in absolute temperature. This temperature is called the critical temperature of water. When the primordial atmosphere was 100 atm (mostly considered carbon dioxide), the first rain fell to the ground when the surface cooled to around 300 C.
After the magma ocean cooled, there was a hot ocean that is unimaginable today. At that time, carbon dioxide was present in the atmosphere in an amount reaching 43 atm, but about 10% of it was dissolved in the ocean that was formed when the temperature dropped below the critical temperature. After the Earth cooled, the partial pressure of carbon dioxide in the atmosphere dropped to about 1 atm over tens of millions of years.
The pillow lava is one of evidences of the presence of the sea. It has a characteristic form because lava was blown into water and cooled rapidly. Oldest pillow lava was found of 3.8 billion years ago in Isua, Greenland. A metamorphic rock made from granite of 4 billion year ago was discovered in the Acasta area in the northern Canada. Granite shows the presence of plate tectonics and the sea.
The sedimentary rock on the surface of the Earth contains carbon which corresponds to as high as 90 atm in terms of carbon dioxide. This pressure is almost the same as Venus' atmosphere. The atmosphere of Venus consists of rich carbon dioxide and nitrogen. At the top of the atmosphere of the same depth of the Earth's one, the temperature is lower than the Earth. Below that there is a dense and high-temperature atmosphere of 50 km. As the altitude lowers and the pressure increases, it gets hotter. It reaches 400 C at the bottom of its atmosphere.
At the time of formation by Giant Impact, the Moon was in the vicinity of the Roche limit (the distance inside where a satellite was destroyed by the tidal force, about 50,000 km from the surface of the Earth). At that time, the Earth rotated about 6 hours, the moon had one lap in 10 hours. Tidal force converts the energy in gravity potential into heat. It is an important mechanism that fundamentally dominates the evolution of the planetary-satellite system, such as heating the entire satellite, changing the internal structure, changing the orbital motion by generating a gravitational torque. It also deformed the solid parts of the Earth, giving it a flattened shape with an equatorial diameter nearly twice that of the polar directions. The mismatch between the Moon's revolution and the Earth's rotation period caused friction due to tidal forces, which slowed down the Earth's rotation and accelerated the Moon, moving away from it. Since the strength of the tidal force is inversely proportional to the cube of the distance from the Earth to the Moon, the effect of tidal friction weakened rapidly, and it is thought that the Earth's surface stabilized over several hundred million years.
After the ocean was formed on the Earth, the great tidal power produced a height difference on the Sea, and it is thought that the height of the wave had reached 1000 m. Supposing that the estimated ancient ocean depth would be 2000 m, a huge and intense wave had been washing the surface of the Earth continuously. On the Archean Earth, arcuate islands formed by plate tectonics were washed away by tidal waves and craters made by gigantic meteors in the late heavy bombardment (4.1-3.8 billion years ago) would be also buried and flattened.
According to a simulation, 2.4 billion years ago a day became longer, at 21 hours. After that, it remained constant for about 1 billion years. This was because the gravitational forces of the Earth and the Moon were balanced. Because the balance was not perfect, the rotation speed slowed down again 700 million years ago, and is now about 24 hours. Over the past several hundred million years, the rate at which the Earth's rotation slows (i.e. the Moon moves away) has also remained almost constant. Using mirrors placed on the Moon during the Apollo program, it has been observed that the current change in the distance to the Moon is 3.8 cm per year.
4.5 billion years ago, the Earth was covered by a magma ocean, but had an atmosphere of gas that seeped out of the magma ocean. After the magma ocean solidified, the atmosphere was replenished by volcanic activity and meteorites. Over time, light hydrogen and helium escaped into space, and stable, heavy nitrogen became the main component. Oxygen was almost nonexistent until 3-3.5 billion years ago.
Hydrogen chloride was dissolved in the rain, so it was strongly acidic. Rain water containing hydrochloric acid dissolved ions such as magnesium, calcium, aluminum, sodium, potassium, iron from rocks on the ground and was neutralized.
After neutralization, large amount of carbon dioxide in the atmosphere dissolved in the primitive ocean, bonded with calcium ions and precipitated as calcium carbonate (limestone). Carbon dioxide contained in the primordial atmosphere fell to about 10 atm and the greenhouse effect of the atmosphere by carbon dioxide was relieved. The primordial atmosphere at that time consisted of 90% carbon dioxide and 10% nitrogen. As carbonate minerals crystallize in hydrothermal vents in the ocean crust, the silicate concentration in the erupting hydrothermal water increases, and calcium ions in seawater decrease, increasing the phosphate concentration.
Impact experiments with small meteorites have shown that meteorites are pulverized on the ocean surface all at once. At that time, organic matter may have been spared from decomposition due to frictional heat. Also, it is possible that the atmosphere acted as a cushion for tiny meteorites, which reached terminal velocity and continued to fall into the ocean. If there were a large amount of tiny meteorites remaining after the formation of the Earth, it is possible that these organic matter were supplied to the Earth.
Among cosmic dust, micrometer-sized particles are decelerated by air resistance and slowly fall to Earth. It is estimated that about 4 billion years ago, meteorites carried several tons of organic matter per year, comets carried several hundred tons, and cosmic dust carried hundreds of thousands of tons. Most of the organic matter in cosmic dust was insoluble and complex.
Heavy metals in the seawater were transported to the mantle by plate tectonics. The early crust, komatiite, sank into the mantle by plate tectonics, and the basaltic crust was formed on the surface. If most of the heavy metals, such as iron, sank as the core, what remained on the surface were oxygen, carbon, nitrogen, silicon, magnesium, sulfur, aluminum, sodium, calcium, etc. Carbon, oxygen, and nitrogen provide the framework for building the organic matter that makes up living organisms. These elements form volatile molecules.
The Sun has experienced eight superflares in the past 12,000 years. In 100 million years, that would amount to 70,000 superflares. It is possible that high-energy particles from superflares produce tens of thousands of tons of amino acids in the Earth's atmosphere each year. When high-energy particles pass through tiny ice particles in space dust, organic matter with a molecular weight of about 1,000 is formed. When this is hydrolyzed in water, it produces molecules such as amino acids.
Let's write down the current heat balance of the entire Earth. From the core to the mantle, it is 7x1012W. The heat supply from radioactive isotopes in the mantle is 20x1012W. To space, it is 46x1012W. Therefore, it is calculated that the core has dropped in temperature by about 1000℃ since it was formed, and the mantle has dropped in temperature by about 400℃.
In the rocks formed by the Earth's plate tectonics system, the oldest one discovered so far is 3.8 billion years ago. A series of rocks formed along with the division of the ocean floor was discovered in Greenland by an International Research Team. Therefore, the system of plate tectonics seems to have started relatively early in ancient Earth. This rock is called an ophiolite, a characteristic layer structure which an oceanic crust is exposed to the ground. It is of thickness about 10 km which is equal to the thickness of the oceanic crust, including various kinds of volcanic rocks.
Plagioclase rocks make up the white areas (highlands) of the Moon. Plagioclase rocks float in magma oceans and were the first rocks to form. The Moon also has rocks called KREEP rocks. They are derived from the last remaining magma when the magma ocean cooled and solidified. K is potassium, REE means rare earth elements and P is phosphorus. K and P are closely related to life. The reason there are no KREEP rocks left on Earth today is thought to be due to erosion. The volcanic activity that followed created the oceanic part. It is basalt.
4.4 to 3.8 billion years ago, the Earth cooled and the oceans formed. The Earth's crust formed, but because of its high temperature, it was not hard enough and did not form into large monoliths called plates. It was also not subducted into the mantle because of its low density. Alternatively, the crust cracked and molten mantle-derived rock erupted from the crack (heat pipes), and cooled rock from the bottom of the crust fell into the mantle (drips). This condition is called stagnant-lid tectonics. The image is of a crust with surface cracks that push against each other and molten rock erupts from the cracks. This form of plate tectonics is observed on planets without oceans.
The atmosphere and oceans were violently agitated by the fall of meteorites and by the tidal forces of the moon, which was at a close distance from the earth. Hundreds of plates crowded together on the Earth's surface during the Pluto Era, but since both plates were young, subduction was unlikely to occur. This led to significant folding of the plates. Magma was not formed from the plates that went under the plates, but was pushed into the mantle where the plates collided, and magma was formed. In this case, folded mountain ranges formed at the plate boundaries, and volcanoes formed along the boundaries. The magma was squeezed from both sides and erupted into the ocean, eventually becoming islands. Arc islands formed and grew along the plate boundaries.
3.8 to 2.5 billion years ago, the crust cooled and hardened, partially forming plates. Rifts (ocean ridges) formed and plates moved and subducted at plate boundaries. Nearby, the plates did not subduct as deeply as they do today; 3 billion years ago, the plates were rich in magnesium and iron (mafic), but 2.5 billion years ago they changed to silicon-dominated (felsic) rocks and became less dense. The lighter crust prevented the thicker continents from sinking into the mantle. Silicon-dominated rocks are formed by water and heat in subduction zones. The oldest felsic rocks date back 3.8 billion years. The formation of zircons suggests that subduction zones existed at this time. Based on rock evidence, a mountain range is estimated to have existed 3.3~3.4 billion years ago.
Isolated subduction zones began to connect 2.8 billion years ago, and global plate tectonics as we know it today was completed 2.5 to 1.8 billion years ago. The first supercontinent, Nuna, was formed at this time. However, the subduction zone did not become as deep as it is today until 800 million years ago, according to rock evidence. Some researchers place the completion of plate tectonics at this time.
Looking at the completeness of living organism in present, I am surprised that hundreds of proteins are involved in one living phenomenon. Common cellular activities include gene replication, gene transcription, translation of mRNA, synthesis of proteins, transport of secreted proteins, processing of proteins, synthesis and degradation of lipids and amino acids, photosynthesis, glycolysis, TCA circuits, ATP synthesis driven by membrane potential, protein degradation, intracellular degradation of organelle, secretion of molecules and so on. Furthermore, duplication of these molecular devices is attained.
Protein is a very complex molecule and functions as a nano-machine. Many kinds of proteins are gathered to create huge structures and work together in series. DNA responsible for genetic information cannot act on its own and always needs assistance of many proteins. In the system from gene to protein synthesis, RNA and proteins cooperate together.
The cell membrane is not merely a shield against the outside world. The protein embedded in the membrane creates a non-equilibrium state on both sides of the membrane to produce energy (ATP) and also sends nerve pulses. Membrane protein also takes extracellular nutrients and catches information molecules. Eukaryotic cells have many folded membrane structures in the cell to make isolated spaces and carry out a special reaction in them.
In fact, in order to elucidate the process of the creation of life, it is necessary to clarify how these functional units were born from inorganic molecules, but also how each functional unit interacts to create an organic relationship among them. Even if these part molecules are prepared and are mixed, living system cannot be born. Was it inevitable that life was born? Or have many incidents stacked in very long time? It is still unknown, and even putative clues for elucidating it are still suspicious.
The essence of life is information. That is, the information that constructs the molecule functionally as an organism is the essence of life. The key to elucidating the birth of life is the birth of information necessary for life, the material basis of information, and the mechanism by which information is replicated to the next generation. Currently, the first genetic information molecule is considered to be RNA. However, we must consider how information on the amino acid sequence of the protein has been written to the RNA molecule.
For the birth of life and its early evolution in several following chapters, I am assembling fragmentary scientific reports into an inevitable story to make a hypothesis on the origin of life.
In order to organize the researches on the origin of life and to align them along the time, I consider how molecular and molecular devices that make up the living body were created from a simple one to a complicated one. The following items are scheduled as follows. Up to "the mechanism of heredity" is the construction of parts, after that it corresponds to the assembly of parts.
But maybe the opposite way of thinking can be possible. It is possible that massive carbon clusters (substances such as graphite or fullerene) were geologically born from carbonate rocks (limestone, etc.) in a reductive environment. Or the possibility that the mountain of carbon decomposes slowly in the seawater to generate macromolecules. As I will repeat in the following chapters, the sufficient density of the molecules involved in life activities is not considered to have been produced naturally according to the second law of thermodynamics. I think that a strong concentrating process is necessary. The story that cells can be made simply by assembling molecules is contrary to the law. Considering that a carbon polymer of mountain size of high energy state was born on the primitive Earth, problems of concentration and molecular aggregation could be solved.
How long has it been until the birth of life? The Hades era was till the late period of heavy bombardment was over at 3.8 billion years ago. After that, until 3.8 to 2.5 billion years ago is called the Archean era. The fossil was found of the first cell (with a membrane structure) about 3.5 billion years ago.
Biomolecules that make up a living organism include carbon, nitrogen, hydrogen, and oxygen as main constituents, and other elements such as sulfur, phosphorus. Carbon and nitrogen constitute the backbone of the biopolymer. Carbon has four arms that form a covalent bond, and nitrogen has three arms. Oxygen has two and hydrogen has one arm. Molecules are constructed in the way that these arms are fully connected. Compounds which have carbon skeletons are called organic substances.
When the sea was appeared, the Earth is covered with thick clouds. At that time, water vapor, carbon dioxide, and nitrogen were turned into reactive radicals by ultraviolet rays from the Sun, particle beams from the space and lightning discharges in the sky. Then chemical reaction among these molecules and the radicals made simple organic compounds, such as hydrogen cyanide, cyanoacetylene, formaldehyde.
There is a large amount of organic raw materials in the Universe. Carbon atoms and water molecules contained in carbonaceous chondrite meteorites and comets are activated by ultraviolet rays and particle beams from the Sun, and simple organic materials are synthesized through chemical reactions. They contain metallic iron, ice, and up to 2-3% organic matter. The Earth was supplied with a large amount of ice and volatile organic materials from meteorites during the late heavy bombardment. The meteorites that fell on the Earth were originally just aggregates of sand grains, so they decomposed at high altitudes before the temperature rose. The particles quickly reached terminal velocity due to friction with the atmosphere, and so the organic matter was brought into the atmosphere without being decomposed.
These molecules dissolved into raindrops and dropped to the sea. There were very few lands in those days. Most of the highly reactive material molecules reacted with water, but sometimes they mutually reacted to form large molecules, stabilized, and accumulated in the primitive ocean.
At bombing into the sea of a meteorite containing metallic iron, reductive atmosphere of ultra-high temperature was temporarily generated in the area. When a meteorite collides with the ocean, a large amount of water instantaneously turns into supercritical water and ultrahigh temperature gas, at the same time, the meteorite and the mineral components of the sea floor evaporated together and became a so-called after-impact steam flow. In ultra-high temperature post-impact steam flow, water decomposes into hydrogen and oxygen. Metallic iron and oxygen in the collision body reacted and became iron oxide. After the collision, the steam flow reached a reduction state of excessive hydrogen at once. Concomitantly, the iron sulfide and the peridotite were evaporated to work as reductive steam flow. As the temperature of the steam flow decreased from ultrahigh temperature, carbon reacted with the hydrogen generated to produce hydrocarbons and various other organic molecules. It is a chemical reaction known as Fischer-Tropsch synthesis and requires a transition metal such as iron, nickel, cobalt as a catalyst. These metal elements also evaporated at high temperature and coexisted in the steam flow.
In the Archeozoic era, there was magnetic field around the Earth due to the convection of the Earth’s metal nuclei, so the upper part of the atmosphere was protected from charged particles coming from the Sun. In the volcanic eruption, many lightning occurs together with reducing gas and water vapor. Reproducing this environment in experiments also made complex amino acids.
Amino acids and nucleobases are well studied as low-molecular organic compounds made first, because these are important components of living organisms. It seems that many other molecules have been synthesized, but they have not been studied much. Organic compounds with a molecular weight of about 1000 are discovered in large quantities from the biological world in large quantities. It also contains many useful substances, such as vitamin or antibiotics. Amino acids and nucleic acids are molecules having about from several to several tens of atoms with a molecular weight of 100-300. From these types of molecules, molecules with a molecular weight of about 1000 were synthesized and accumulated by catalytic action of high concentration metal ions in the hydrothermal vents at the bottom of the sea through thermochemical reactions. Those molecules contain multiple functional groups in one molecule and would assemble to form the base for a new chemical reaction.
Amino acids are synthesized through the famous reaction starting from aldehyde and hydrogen cyanide, ammonia. Besides that, decomposition of nucleic acid bases can be considered. Saccharides with simple structure can be synthesized from formaldehyde. The mineral consisted of boric acid acts as a catalyst. Although sugar has many three-dimensional structures even with the same molecule, among them, fructose, glucose, and mannose are stable, and it is considered that the sugar plays an important role in origin of life.
A cyclic molecule consisted with 6 or 5 atoms of either carbon or nitrogen, alternatively bound via single and double bonds, is called a hetero ring. Adenine, one of the nucleobases, has a heterocyclic structure in which hexagons and pentagons are fused. Adenine can be relatively easily synthesized from hydrogen cyanide and ammonia. Heterocyclic molecules containing nitrogen like adenine are bonded to each other weakly by hydrogen bonds and are easy to make complexes with metals. As it contains double bonds in a molecule, two double bonds react and tend to polymerize via radicals. Because it is easy to decompose with ultraviolet rays, the nucleobase is unstable at the surface of ground or in the sea, where the ultraviolet rays reach.
The image of stagnant-lid tectonics in the Earth in Hadean era is as following. Hot magma from the mantle erupts from cracks in the crust, was cooled by the ocean, and solidified. This process was repeated, forming an undersea mountain range around the heat pipe. When a huge mountain range of basalt was formed, the supply of magma was cut off from underground, and the mountain range cooled and sank. At the same time, it dragged in the surrounding crust, made distant crust stretch and crack, forming new heat pipes. The undersea mountain range of basalt sank into the mantle, where its bottom was melted by the heat and fell into the mantle, finally it stabilized as a slightly thicker crust.
As the undersea mountains was sinking, faults were forming and many hydrothermal vents were also formed. As the Earth cools, the water-containing plates thickened, and the heat pipes turned into ocean ridges, gradually changing into plate tectonics. In the ancient Earth, high-temperature oceans spread out, and the water vapor rising from them formed thick clouds that blocked out the sunlight.
Cyclic organic compounds having a benzene ring or a hetero ring are indispensable for basic molecules of living things. These organic substances are easily decomposed by ultraviolet rays. Organic seed molecules were synthesized in the sky and on the ground, but dissolve in rain and fall into the ocean where ultraviolet rays cannot reach. The place where biological macromolecules necessary for living organisms were born, preserved, and formed higher-order structures (this is called chemical evolution) was on the ocean floor where ultraviolet rays could not reach.
The first candidate of the place of birth of life is around the hydrothermal vent on the seafloor. One of the reasons is that hyper-thermophilic bacteria are located at the trunk (starting point) of molecular evolutionary tree. On the Earth in present, superheated bacteria are isolated from the hydrothermal vents of the seafloor. Other candidates, such as in volcanic activity on the ground (hot springs), collision of meteorites, and lightning, are lacking of stability in view of energy supply for millions of years.
Seawater from black smokers formed in the hydrothermal area contains high concentrations of hydrogen. Hydrogen is generated when peridotites in the mantle react with hot seawater and turn into serpentine. In the proto-Earth, komatiite, formed by rapid cooling of magma, formed the crust, so komatiite is considered to be the source of hydrogen. At the present seafloor, hydrogen concentration of about 20 mmol is observed in the hydrothermal area originating from the ridge in the deep sea of 500 atm or more. Hydrogen is essential for reducing carbon dioxide to produce organic matter. An oxidation-reduction potential is formed around the hot water jet, thereby providing a fuel engine with stable performance due to a difference in concentration of a substance and a difference in temperature. It is convenient for the synthesis of organic compounds.
Furthermore, the seawater from the hydrothermal vent contains more than 1000 times more metal ions such as iron, manganese, copper, zinc than ordinary seawater. Metal ions act as a catalyst for polymerizing organic substances under high temperature and high pressure.
The hydrothermal vent is in an environment of high temperature (200-350 C) and high pressure (200-300 atm), and a large amount of heat energy is constantly supplied. Cold seawater infiltrated from the cracks of the ocean floor is heated in the bottom of crust, rises up the jet hole, blows out into the cold seawater, and is cooled again. The heating / cooling cycle of seawater occurring in the hydrothermal vents is reasonable when considering chemical evolution. Organic polymers that play a central role in life activities are unstable in high temperature environments. Organic materials synthesized at high temperature were immediately cooled at the sea bottom hydrothermal vent, so it was possible to avoid decomposition by heat.
As the sea water circulates, the organic molecules have passed through the hydrothermal vents many times over the flow and have grown into more complex molecules. Polymer compounds were filtrated from seawater containing organic matter when passing through mud, rock or crust, and being precipitated and concentrated there. For example, when considering that the reaction has progressed one step at each cycle, it fits well with the fact that the biopolymer is a linear homopolymer.
Biopolymers are generally linear homopolymers of amino acids, nucleobases, sugars. There are reports that amino acids and nucleotides adsorbed on the surface of clay minerals are polymerized, suggesting one of polymer formation mechanisms. In ancient times, low molecular weight organic compounds such as amino acids, nucleobases, sugars, fatty acids, hydrocarbons, etc. bonded to regular crystals (the surface of minerals) become polymers (linear homopolymers), this is one of theory on chemical evolution.
Another theory is to think about oil production. It is possible that sediment containing a lot of organic substances buried in the ground, undergo dehydration reaction under high temperature / high pressure in the underground, and turned into a substance like petroleum containing a large amount of unsaturated carbon bond. Petroleum-like low molecules tend to cause chemical reactions and easily polymerize at normal temperature and pressure. If a massive amount of organic matter was buried and became petroleum, it would have formed a layer like current petroleum and a high concentration of organic resources would have been generated.
Volatile organic molecules decompose with ultraviolet irradiation or such rays falling over in the sky on the primitive Earth. Nonvolatile organic molecules are dispersed in the sea. Molecules with small density and of water-insoluble like oils floated and agglomerated on the sea surface. In that case, it is decomposed on the sea surface where ultraviolet rays are falling or it is radical polymerized into a polymer. Water soluble molecules such as amino acids, nucleic acids and sugars dissolve in seawater, adsorb to clay minerals and precipitate on the seabed. In general, biological organic molecules have high affinity for clay minerals.
The hypothesis that life was born on the ground, such in shallow sea or lake, has advantage in view of enrichment. Concentration of substances occurred on the surface from the tidal dry-wet cycle, which led to synthesis of macromolecules. The problem in pre-life evolution and chemical evolution is the mechanism of supply of macromolecules and how the combination and structuring of macromolecules to create life phenomena have been achieved. At present, several proven synthetic reactions have been reported, and it is likely that living organisms will be formed if they are conveniently combined. However, no matter how you describe it, the drawback is that it looks like expediency.
Ammonia and cyan produce numerous polymers containing nucleobases. As this process proceeds simultaneously, explosive number of types of compounds are produced. However, under the presence of phosphoric acid, these reactions are limited to some extent. In the experiment, 2-aminooxazole is synthesized in the presence of phosphoric acid. This compound is a promising precursor of nucleic acids containing pyrimidines. Also, it is volatile and easily solidifies. That is, 2-aminooxazole is possible to be concentrate by increasing and decreasing the temperature. In the process of synthesizing a nucleic acid containing pyrimidine from 2-aminooxazole, there is no need to consider the reaction in which a sugar, a nucleotide base and a phosphate group are bound, which is one of the keys of nucleic acid synthesis on the primitive Earth.
Chlorophyll and hemoglobin (heme) are molecules in which heterocyclic molecules are coordinated to metal ions (magnesium for chlorophyll and iron for heme), to form complexes. Heterocyclic molecules such as nucleobases absorb ultraviolet rays and become activated. Molecules with many heterocyclic molecules, such as nucleic acids, are activated by UV light. Complex molecule composed of heavy metal ion and heterocyclic molecule may catalyze the reaction between water and carbon dioxide with energy of light. These molecules might have been born on the ancient Earth, and formaldehyde was made in large quantities from water and carbon dioxide by catalysis of metal ion activated by heterocyclic molecules which gather sunlight energy.
When carbon dioxide and hydrogen react with the catalyst of a heavy metal complex, formaldehyde is formed. Formaldehyde is a reactive substance and has the property of polymerizing itself, resulting in paraformaldehyde or a sugar. In addition, it reacts easily with chemical groups forming a hydrogen bond. As a result, intramolecular and intermolecular bond are formed. Molecules in living organisms, such as sugars, proteins, and nucleic acids, that make up the living body have abundant hydrogen bonds and react with formaldehyde. Among alkaline liquids, formaldehyde undergoes a polymer synthesis reaction which produces various sugars. The macromolecule of sugar is insoluble and highly reactive.
Further to imagine, the heterocyclic molecules-heavy metal ion complex, which produces formaldehyde from carbon dioxide using light energy, was linked each other by products, then stabilized and accumulated in large quantities. I think this is the origin of photosynthesis.
On the other hands, the reaction that reduces iron sulfide with hydrogen sulfide to produce pyrite reduces carbon dioxide to form formaldehyde and formic acid. In the deep sea where sun light cannot reach, carbon dioxide assimilation by chemical energy spontaneously occurred. The iron sulfide produced as a result is insoluble and precipitates in the form of a foam. The catalytic center of carbon dioxide assimilation may be encapsulated in an iron sulfide capsule and serve as a source of cells. It is called the Hall & Russell hypothesis. The only energy source for Archean organisms was to reduce carbon dioxide with hydrogen. Hydrogen sulfide and ferrous iron coexist without reacting with carbon dioxide in the same reducing environment. Hydrogen was generated from the hydration reaction of peridotite, the main component of the mantle, and was supplied from hydrothermal vents.
The hot water ejected from the seabed floats and rapidly mixes with the surrounding cold seawater. While rising, the dilution of hot water progresses steadily, and when it reaches about several hundred meters from the seabed, the temperature (density) of hot water becomes equal to that of the surrounding seawater. The original hot water that has lost buoyancy spreads horizontally on the equal density surface. The original hot water is diluted but contains fine sulfide and oxide precipitates.
