Life is the most wonderful and fascinating natural phenomenon. Today, there are more than 6.5438+0.5 million species of animals, more than 400,000 species of plants and more than 200,000 species of microorganisms on the earth, which constitute a life world full of butterflies, birds and flowers, beautiful scenery, colorful reproduction and evolution, and endless life. From mountains to plains, from deserts to grasslands, from the air to rivers and lakes.
However, 4.6 billion years ago, when the earth was formed in the universe, it was not only hit by hundreds of millions of comets and meteorites, but also took about 654.38 billion years to lower the temperature by several thousand degrees Celsius. At that time, the earth was a lifeless and desolate world. After about 654.38 billion years, it seems that simple cyanobacteria appeared on the earth. Therefore, for the first time on earth, this is a question that people are generally concerned about the origin of life on earth.
The origin of life is an important scientific topic in contemporary times, but it is also the most basic biological problem that is little known so far. In this article, we will introduce several theories about the origin of life.
There have been various hypotheses about the origin of life in history, such as "God's Creationism" (that life is created by God or God) and "Spontaneous Generation" (that life, especially simple life, occurs naturally from inanimate matter). Most of these hypotheses are based on speculation and have been denied by people. Judging from the research papers put forward by the international conference on the origin of life held in recent years, contemporary hypotheses about the origin of life can be divided into two categories:.
The theory of chemical evolution holds that life originated from a series of chemical evolution processes from inorganic to organic and from simple to complex under the condition of primitive earth, while the theory of cosmic embryology holds that the original life on earth came from outer space of the earth and only developed on the earth later.
Chemical evolution theory
Biological molecules such as nucleic acid and protein are the material basis of life, and the key to the origin of life lies in the origin of these biological substances, that is, on the lifeless primitive earth, abiotic substances produce various organic substances and biological molecules through chemical action due to natural reasons. Therefore, the origin of life is first of all the origin and early evolution of primitive organic matter. The role of chemical evolution is to create a class of chemical substances, which constitute common "structural units" such as amino acids and sugars, as well as life forms such as nucleic acids and protein.
1922, biochemist Oberlin was the first to put forward a verifiable hypothesis, that is, some inorganic substances on the primitive earth became the first organic molecules under the action of energy from lightning and the national emblem sun. After a lapse of 3 1 year, American chemist Miller first experimented with this hypothesis in 1953. He is like the atmospheric composition on the primitive earth. Ammonia and steam, etc. Organic amino acids were synthesized by spark heating and discharging. After Miller, many other important biomolecules, such as purine, pyrimidine, ribose, deoxyribose, nucleoside, nucleotide, fatty acid, porphyrin and lipid, were synthesized under the condition of simulating the primitive earth. +0965 and 19865438+ insulin and yeast alanine transfer ribonucleic acid were synthesized for the first time in China. Protein and the formation of nucleic acid are the turning point from inanimate to living. The successful synthesis of these two biomolecules has opened a new era of synthetic life to study the origin of life.
Generally speaking, the chemical evolution of life includes four stages: from small inorganic molecules to small organic molecules; Forming organic macromolecules from small organic molecules; From organic macromolecules, a multi-molecular system that can maintain its own stability and development; From a multi-molecular system to primitive life.
Cosmic embryo species theory
In the past and now, many hypotheses belonging to the theory of cosmic embryo have been put forward. For example,1put forward at the 10th International Conference on the Origin of Life in July, 1993 that "the organic substances that cause chemical reactions and lead to life are undoubtedly brought by comets that collide with the earth"; Others infer that one of the comets that collided with the earth crossed the universe with a "life embryo" and left it on the newborn earth, thus giving birth to life on the earth. A few years ago, a space physicist and an astrophysicist also explained the origin of life on earth as: the source of life on earth may come from one or several comets that fell into the ocean four billion years ago, and they also believed that comets provided the raw materials needed for the birth of life on earth (they called them "comets").
Although some scientists have strong objections to this hypothesis (they think that "comets bring some substances, but they are not decisive, and the substances necessary for life already exist on the earth"), although this view is still a problem that needs further proof, through the exploration and research of organic molecules on meteorites, comets, interstellar dust clouds and other planets, we can understand the formation and development laws of those organic molecules and compare them with those on the earth.
The origin of cells
The birth of primitive life with primitive metabolism and self-reproduction ability marks the end of the chemical evolution stage of life origin and the beginning of the biological evolution stage.
The basis of life activities is a series of chemical changes, which are all completed under the catalysis of enzymes. The inheritance of life depends on the replication process of DNA. Primitive life is autocatalytic, and it needs a certain material basis to develop into stacking catalysis. It also needs a certain morphological structure. Cells are basic structural units and functional units with complete life functions, including enzyme catalysis and DNA replication. Primitive life was acellular at first, and then evolved into a cellular form, which was another qualitative leap. This process is the origin of cells in the origin of life. Cell origin is an important part of the origin of life.
The Significance of Studying the Origin of Life
Studying the origin of life is to find out the history of the birth of life for billions of years. But its significance goes far beyond tracing to the source, and lies in understanding the relationship between life and environment, whole and part, structure and function, micro and macro, individual development and system development, subject matter and energy and information, which can further clarify the mechanism of life activities such as genetic variation, growth and differentiation, reproduction, metabolism, exercise induction and regulation, so as to understand and clarify the essence of life and realize human control.
Although the study of the origin of life and cells is an attempt to reconstruct a distant historical process, unlike most other research fields, the complete origin process cannot be repeated in the laboratory. But you can simulate the test step by step in the laboratory. Therefore, to study the origin problem, on the one hand, we should find the answer in nature, on the other hand, it is more important to carry out simulation research at various stages of evolution in the laboratory. Carry out research on synthetic living matter and synthetic cells. These studies not only help to clarify the origin of life and cells, but also guide people to synthesize life materials, cells and even life according to their needs, and realize the ultimate goal of life science-controlling life and transforming life.
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The origin of life is an eternal mystery. When and where did life on earth come into being? How did it come into being? For thousands of years, people have encountered many traps and seen unprecedented light when solving this mystery. The first mystery of the origin of life is the time of its origin. The second question is the way in which life originated. How did life originate? Where did it originate?
Since ancient times, there are many theories to explain the origin of life. Such as western creationism, China's Pangu creationism, etc. But it was not until the19th century that with the publication of Darwin's On the Origin of Species, great changes took place in biological science, and at the same time it brought a glimmer of light to reveal the eternal mystery of the origin of life, which is the modern chemical evolution theory. The chemical evolution theory of the origin of life was first proved by an American scholar Miller in 1953. What should the events about the origin of life described by Miller look like? That is, in the early days, the earth contained a large number of reducing primitive atmospheres, such as methane, ammonia, water, hydrogen and primitive oceans. When lightning struck the earth in the early days, these gases polymerized into various amino acids, which may be partially concentrated at normal temperature and pressure, and then further evolved into protein, other polysaccharides and polymer lipids, which may be pregnant and developed into life in a certain period of time, which is described by Miller.
Life on earth may have been born 3.8 billion to 4 billion years ago, but we should be soberly aware that we still have a long scientific journey to solve the eternal mystery of the origin of life. The evolution from inorganic matter to organic matter, from organic compounds to organic life is also very accidental. It is not such an environment. Only with such conditions can life be produced. Someone once said that these inorganic substances are like a garbage dump, which contains everything, such as plastics, plastic bottles, iron, scrap metal and oil. Life, a single cell, is like a beautiful Mercedes-Benz. After a typhoon, these wastes were assembled into a Mercedes-Benz. Therefore, we can imagine the process of the origin of life is very, very difficult. Therefore, maybe we are the only paradise for life on this blue planet, so please protect our earth and cherish life on it. We can't expect the second origin of life on earth.
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Hello, everyone. Today I'm going to talk to you about the mysterious origin of life. The origin of life is an eternal mystery. When and where did life on earth come into being? How did it come into being? For thousands of years, people have encountered many traps and seen unprecedented light when solving this mystery. In the Spring and Autumn Period 2500 years ago, Lao Tzu wrote in the Classic of Tao Te Ching that the Tao gives birth to one, two, three and three things. In today's words, life on earth has evolved slowly from less to more. They have a common ancestor, this ancestor is one, this ancestor is born in heaven and earth, in today's words, it may be formed in the inorganic world.
In the Middle Ages, it was also very popular in the West that God described in the Bible created everything in seven days. Today, the origin of life is not as described in these ancient legends or myths, but shows that human beings have devoted great enthusiasm and attention to the mystery of the origin of life for a long time. But how should the origin of life happen? How does science explore this eternal mystery? What progress have we made? What other problems remain unsolved? This is what I want to introduce to you today.
First, the origin of life, the first mystery is the time of life, the time of origin. In the Western Middle Ages, people believed in the story of God creating man in the Bible. 1650, an Irish archbishop calculated the exact time of God's creation according to the description in the Bible, and another priest even calculated the creation time more accurately to 9: 00 a.m. on June 23, 4004 BC. In other words, the origin of life is 6000 years ago, which is certainly not true, but what is it? That's a really scientific answer. How does science answer the time of the origin of life? That is to say, to answer with fossils, fossils are preserved in rocks. We know that after the death of living things, their remains are preserved in rocks under appropriate conditions. We call it a fossil. Rock formations formed in geological history, like a chronicle, are buried deep in these rocks, and older biological fossils are preserved at the bottom of the rock formations.
So far, we have found that the oldest biological fossils are rocks from western Australia, about 3.5 billion years ago. These fossils are similar to modern cyanobacteria. They are some primitive life, invisible to the naked eye. Its size is only a few microns to tens of microns, so we can say that the origin of life is not later than 3.5 billion years. At the same time, we know that the earth was formed about 4.6 billion years ago. With these two data, we can see the age of the origin of life, which can be roughly defined between 4.6 billion and 3.5 billion years. Today, with the development of science, geologists believe that in the early days of the earth's formation, the earth was hit by a large number of asteroids and meteorites, which was not suitable for life. It was not so much that there was life on the earth at that time as that it was destroying life, so the origin of life on the earth was not earlier than 4 billion years. In addition, carbon was found in rocks in Greenland 3.85 billion years ago. As we know, there are two kinds of carbon, one is inorganic carbon and the other is organic carbon. In addition, this kind of carbon can be divided into heavy carbon and light carbon, so we can infer the source of these carbons according to the ratio of light carbon to heavy carbon in this kind of carbon. According to the isotope analysis of carbon, scientists speculate that it is organic carbon and comes from organisms. That is to say, in this way, we have greatly shortened the time of the origin of life, that is, between 4 billion and 3.8 billion years, from the origin of life on earth to the present, it is an endless evolutionary history of life.
Ok, first of all, we now have the concept of the origin of life, from 4 billion to 3.8 billion years ago. So how did life originate? Where did it originate? So we should review some hypotheses about the origin of life.
The first is creationism. In the first chapter of the Old Testament, God created everything in the world in seven days. This concept was generally accepted in the Middle Ages in the West. It can be said that this concept has been accepted by many people until now, and of course it is not established. The second is the theory of autogenesis. For example, the Greeks believed that insects were born in the soil, everything was renewed in spring, seeds sprouted from the soil, and insects broke out of the eggshells left last year. But this is not the origin of life, but the continuation of life. It can be said that this theory of autogenesis has now been completely abandoned. Similar to this statement, for example, the Egyptians believed that life came from the Nile, and there was a saying in ancient China that there were decayed grass fireflies.
The third hypothesis about the origin of life is the theory of biogenesis, which is also quite popular in the west in the19th century. The theory of student origin holds that life is inherent in the universe. If you want to ask me where life comes from, you must first answer me a question: how did the universe originate? How did this happen? You gave me an answer about how matter comes from, so I can say where life comes from. In fact, this is an agnosticism. In the second half of the 20th century, the theory of biogenesis gradually developed to the present theory of cosmic embryo species. Up to now, many scientists believe that it takes hundreds of millions of years to form enzymes necessary for life, such as protein and genetic material, and there is not enough time to complete these processes in the early earth. Because it is only 200 million years old, they think that life must have come to the earth from somewhere in the universe in the form of spores or other life. This concept also has some evidence.
Since the 1940s, nearly 100 kinds of organic molecules, such as formaldehyde and amino acids, have been detected by means of astrophysics. Two of these celestial bodies can be related to life on the earth, and may bring life or organic molecules to the earth. One is a comet and the other is a meteorite. We know that these two celestial bodies contain a large number of organic molecules. For example, we call some comets dirty snowballs. They contain not only solid water, but also organic compounds such as amino acids, iron, ethanol, purine and pyrimidine, and life may be produced on comets and brought to the earth. Or when comets and meteorites hit the earth, these organic molecules undergo a series of syntheses to produce new life. Of course, this embryology also has different ideas. It has two fatal weaknesses. One is whether life can migrate in the universe for a long time. Can you survive? We know that the distance between celestial bodies is calculated in light years, and the communication between celestial bodies may take thousands of years, from one planet to another. In this vacuum, exposed to this large amount of cosmic rays, can living life continue to sprout after thousands of years? This is the biggest problem, the second process from inorganic molecules to organic compounds. This process, for example, we saw the formation of small organic molecules on comets, and it can also be formed on earth, which is beyond doubt.
From 65438 to 0859, with the publication of Darwin's On the Origin of Species, great changes have taken place in biological science, and at the same time, it has brought a ray of light to reveal the eternal mystery of the origin of life, which is the modern chemical evolution theory. The chemical evolution theory of the origin of life was first confirmed by American scholar Miller in 1953. Since you said that the temperature of the earth was relatively high in the early days, reducing gases and water were everywhere, I put these gases and water in a bottle to see if life or organic compounds could be produced. 1953, Miller put ammonia, hydrogen, water and carbon monoxide in a sealed bottle, inserted metal rods at both ends in the bottle, and then turned on the power. Through this lightning action, a large number of amino acids were indeed produced in a few days. That is to say, on the earth, under lightning and at room temperature, it can also become inorganic molecules and synthesize organic molecules. We know that your amino acid is the most important substance that constitutes protein, and it can be said that it is the most important substance that constitutes the origin of life. So, what should Miller's description of the origin of life look like? That is, in the early days, the earth contained a large number of reductive primitive atmospheres, such as methane, ammonia, water, hydrogen and primitive oceans. When lightning struck the earth in the early days, these gases were polymerized into a variety of amino acids, which may be partially concentrated at normal temperature and pressure, and then further evolved into polysaccharides such as protein and protein, as well as polymer lipids, which may be pregnant and developed into life at a certain time.
However, this kind of warm pool also encountered some problems, including two problems. The first problem is that geologists now believe that the early atmosphere of the earth does not contain a lot of reducing gases, but contains a lot of carbon dioxide and nitrogen, which is more inert than Miller gas. In the case of lightning, you can't form a lot of amino acids. Second, it is impossible to form a warm pool in the early days of the earth for a long time. Why? Because at that time, in the early days of the earth, as I said just now, there were a lot of meteorites and meteors, and the temperature was very high with the radioactivity of the earth itself. Once life is born in your warm pool and a meteorite hits it, the temperature can reach thousands of degrees or even thousands of degrees in an instant, and life is extinct, so you can only regain the origin of life. But now we think so. Are there any relatively high temperatures, reducing gases and living things on the earth today? Then, two works can be said to be of epoch-making significance. One is 1967, an American scholar, Blake, who found a large number of thermophiles in the hot springs of Yellowstone National Park. We know that protein generally freezes when it exceeds 60 degrees, and eggs will be cooked at 60 degrees or above 70 degrees. But can living things survive above 60 degrees? I didn't dare to think about it before
The second one is Chris of 1977. He also found a large number of thermophilic microorganisms in hot springs on the bottom of the Pacific Ocean. This temperature is higher, possibly reaching 200 to 300 degrees. What about its pressure, 200 to 300 atmospheres? What is its environment like? It does contain many reducing gases, such as hydrogen sulfide, methane, hydrogen and carbon monoxide. This environment is very similar to that of the early earth 4 billion years ago. So did the origin of life come into being at this time? This is what we see now, but are there any microorganisms found in craters or hot springs in fossils? Indeed, in this respect, we have also made very important progress in fossils. For example, in 2000, Australian scientist Rothmason discovered a large number of well-preserved filaments in volcanic sediments in Australia about 3.2 billion years ago. This shows that 3.2 billion years ago, life existed in large quantities near hot springs, so this is the latest, most popular and so far the most scientific hypothesis about the origin of life, that is, life originated near hot springs or undersea hot springs, commonly known as "black chimney".
Underwater hot springs and terrestrial hot springs have many common characteristics. First of all, its temperature is very high. Secondly, it contains a lot of reducing gases, besides carbon dioxide, there are carbon monoxide, hydrogen, ammonia and hydrogen sulfide. The third feature is that they all contain a large number of organisms, such as cyanobacteria, photosynthetic bacteria, sulfur bacteria, especially a class of archaea, which are extremely vigorous at high temperature. If it exceeds 100 degrees, it will flourish in large quantities. If you leave such an environment, such as the temperature drops, you will immediately go to sleep and cannot live normally. So do these creatures represent the earliest and most primitive time of the origin of life on earth?
In the early days, the temperature of the earth was very high, and the earliest life forms should be some creatures that can adapt to high temperature, while in hot springs, creatures are just thermophilic microorganisms. Secondly, there are many similarities between the hot spring environment and the early earth environment, for example, it has high temperature and a lot of reducing gases, such as carbon monoxide, hydrogen, ammonia, hydrogen sulfide and so on. Thirdly, in the high-temperature hot water environment, it is beneficial to dehydrate small molecular organic compounds and polymerize them into organic polymers. For example, we now use small organic amino acids to synthesize protein, that is, in hot water, this polymer is formed after dehydration through this thermal polymerization reaction, especially near this hot water port, pyrite is formed, commonly known as "fool gold". It consists of sulfur and iron. On its surface, it is very beneficial to the synthesis of polymers, because this kind of iron sulfide surface is a very good natural catalyst. The fourth favorable evidence is that there is a gradient of temperature and hydrochemical identification between the hot spring mouth and the surrounding seawater. This gradient is also beneficial to the continuous reflection of various chemicals. As we know, when the hot spring spouts, its temperature may reach 200 to 300 degrees, especially near the mid-ocean ridge on the seabed. If the temperature of the sea water is 0, the temperature of this seabed is generally 0 to 4 degrees. In this case, from 300 degrees, it has been. The fifth and most important point is that the creatures in hot springs are indeed the fastest-evolving root-type creatures, that is, their genes are the oldest types.
Modern biologists have compared some thermophilic archaea in hot springs with ordinary bacteria through the study of biomolecules, and found that their genetic similarity is less than 60%. That is to say, these archaea contain a lot of ancient genes, which means that this type is probably the origin of life. It should be said that the best evidence for us to study the origin of life is the information contained in rocks and fossils between 4 billion and 3.8 billion years on earth. However, after 4 billion years of changes, the earth has changed beyond recognition. Even if you have rocks from 4 billion to 3.8 billion years old, it has entered a large number of varieties with little information.
Therefore, we should not confine our eyes to the earth. If life is a common phenomenon in the universe, is there an environment similar to the early earth on other celestial bodies besides the earth? If so, it may open a new window for studying the origin of life. Where is our first goal? Not Mars, but the moon. Now geologists believe that the moon was 4 billion years ago, when a big planet hit the earth and disappeared from it. Today's moon was formed, which happened to be 4 billion years. If there is the origin of life on the earth, let's look at it on the moon, then this problem will be solved. China ancient mythology has the Goddess Chang'e flying to the moon's saying that there are laurel trees, moon rabbits and romantic love stories on the moon. But in the 1960s and 1970s, with the successful landing of astronauts from the former Soviet Union and the United States, this myth was completely shattered. The moon is actually a desert planet without life, water and oxygen, which is not suitable for life.
So what's our second goal? The second goal is Mars, because Mars probably had an Earth-like experience 4 billion years ago. Its material composition is very similar to that of the earth, and its orbit is also very similar to that of the earth. So is there life on Mars? What are we going to do on Mars? When we look for the origin of life, where should we start? Generally speaking, it is three o'clock. Are there creatures on Mars? If there is living life, that's good. Life may really have originated in the universe, or life on earth may have come from Mars or other comets. Secondly, we look for liquid water, because we know that water is the source of everything and water is the source of life. Now all the life forms we understand on the earth are inseparable from water, so finding liquid water is also a very important indicator. The third is to find compounds related to life. If we don't have living things now, did we have them in the past? Did the creatures of the past form some compounds? Are they preserved in these rocks in the form of fossils? So we go to Mars to find life for three purposes.
1957 when the American Viking spacecraft sent back information to the earth, there was no life and no liquid water on Mars. It is a barren and thirsty red planet. However, mankind is not discouraged. In 1990s, NASA accelerated its exploration of Mars. Images obtained by Mars probe, Mars Pioneer spacecraft and Hubble telescope, as well as other astrophysical information, indicate that liquid water may have existed on Mars in the past. According to some space data, in front of the mountain where we had a big flood, there were structures similar to alluvial fans on Mars, as well as traces of water, rivers, rivers like the dry riverbed on the earth, and water eroding rocks. In addition, there is something very special. At the poles of Mars, a phenomenon similar to the thawing of frozen soil on the earth was found. This is our spatial information.
But if we have instruments, bring instruments and people, explore on Mars, or get a stone to analyze, won't these things be clear at a glance? Therefore, at the beginning of 1999, the United States launched a Mars polar lander with sophisticated analytical instruments, ready to conduct a careful study in the polar regions of Mars. Unfortunately, at the end of 1999, these instruments are expected to get direct information about whether there is water on Mars, but they lost contact with the Earth as soon as they entered the Martian atmosphere.
So our research on Mars is helpless? At least not at this stage. We have meteorites from Mars. Fortunately, in 1984, a meteorite was found on the Antarctic ice sheet. After this meteorite was brought back, we analyzed its elements and gas chemistry and found this meteorite. Its gases and isotopes are very similar to those on Mars. So they think this meteorite came from Mars. This meteorite fell on the ice sheet 10 thousand years ago, the ice sheet in Antarctica.
According to the radioisotope dating of this meteorite, this meteorite has a history of 4 billion years, which is about 4 billion years from now, which is completely consistent with the age of the origin of life on earth. So for decades, scientists have done a lot of research on this meteorite. Some researchers believe that this meteorite contains signs of life. What evidence is there? There are three. The first one contains several sedimentary minerals. Because sedimentary minerals are formed in the presence of water, scientists infer that there may be water on Mars, especially one of these minerals is a magnet mineral. He believes that this kind of magnetite can only exist in the form of life, which is the first evidence. Secondly, through the chemical analysis of the surface of this meteorite, a variety of polycyclic aromatic hydrocarbons were obtained. He believes that this polycyclic aromatic hydrocarbon is related to life forms. Thirdly, through careful observation by scanning electron microscope, biological fossils very similar to bacteria were found. This fossil is not very big, only a few hundred nanometers. Therefore, in 1996, NASA announced to the world that there was life on Mars 4 billion years ago. Of course, this is a family statement. Is the information about the existence of life in this meteorite true? Of course, many scholars have questioned the evidence. First, take magnetite as an example. You think it can only survive by life, and I agree with you. You think this sedimentary mineral is also survived by life, and I agree with you. Only life with water can precipitate, and I agree. But you should know that this meteorite was found on the Antarctic ice sheet. The ice is full of water. When you hit the ice sheet, a lot of water will melt. When a meteorite hits the earth, many cracks may be formed. If liquid water and melted water enter through this crack, won't it also form a sedimentary mineral of its own? In addition, if you think this magnetite, you may also, if some people think that magnetite is not unique to life and can be formed under other material conditions, then if the first evidence is given, many scientists think that it cannot be occupied. The second is the problem of polycyclic aromatic hydrocarbons. Similarly, if you look like the Antarctic ice sheet, it is MINUS 40 degrees or 50 degrees, and there are also a lot of bacteria and algae. Is it polluted? The pollution now may have been ten thousand years ago. So this evidence, you can't say it is a very reliable evidence, 100% evidence. The third evidence, especially the third evidence, is even more unreliable. Is to split the meteorite. Look at these so-called bacterial fossils. These fossils, the first one, are too small, only a few tens of nanometers in diameter. We know that if you are like an iron core, it may be 0.6 nanometer, then your so-called biological fossils may be hundreds or even thousands of cores. So this basic word, the smallest form of primitive cells that we understand now, is unimaginable. So whether there is life on meteorites, or whether there is life on Mars, needs further study.
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