1. Spontaneous generation theory
Spontaneous occurrence theory is a widely popular theory before19th century, which holds that life occurs naturally from inanimate matter. For example, in ancient China, it was thought that "rotten grass turned into fireflies" (that is, fireflies were produced by rotten haystacks), and carrion gave birth to maggots. In the west, Aristotle (384-322 BC) was a naturalist. It has also been proved by "experiments" that mice will be produced after 2 1 day by stuffing grain and worn-out shirts into bottles and putting them in the dark. To his surprise, this "natural" mouse is exactly the same as ordinary mice.
/kloc-in the 8th century, the Italian biologist Spalanjani (1729-1799) found that if the broth was heated in a flask, boiled and cooled, if the flask was opened, many microorganisms would multiply and grow rapidly in the broth. But if a cotton plug is added to the bottle mouth and the same experiment is carried out, there will be no microbial reproduction in the broth. Sparranjani thinks that the small creatures in the broth come from the air, not naturally. Spalanjani's experiment laid a solid foundation for scientists to further deny the theory of spontaneous occurrence.
1860, the French microbiologist pasteur designed a simple but convincing experiment, which completely denied the theory of spontaneous occurrence (for details, see the first volume of Biology, the standard experimental textbook for compulsory education).
2. Theory of chemical origin
The theory of chemical origin is a widely accepted hypothesis of the origin of life. This hypothesis holds that life on the earth evolved from inanimate matter step by step after the earth's temperature gradually dropped through an extremely complicated chemical process in an extremely long time.
The theory of chemical origin divides the origin of life into four stages.
The first stage, the stage of generating organic small molecules from inorganic small molecules, that is, the chemical evolution process of the origin of life was carried out under the conditions of the primitive earth, which has been mentioned in the textbook, so I will not repeat it here. What needs to be emphasized is Miller's simulation experiment. In this experiment, a flask filled with aqueous solution represents the primitive ocean, and its upper spherical space contains "reducing atmosphere" such as hydrogen, ammonia, methane and water vapor. Miller first heats the flask to circulate steam in the tube, and then he discharges through two electrodes to generate an electric spark, which simulates lightning in the primitive sky, thus stimulating different gases in the sealing device to react chemically. The condensation tube connected to the lower part of the spherical space cools the reaction products and steam to form liquid, which flows back to the flask at the bottom, that is, simulating the process of rainfall. After a week of continuous experiments and cycles. When analyzing its chemical composition, Miller found that it contains various new organic compounds, including five amino acids and different organic acids. At the same time, it also forms cyanohydric acid, which can synthesize adenine, which is the basic unit of nucleotide. Miller's experiment tries to prove to people that the first step of the origin of life, the formation of organic small molecular substances from inorganic small molecular substances, is completely possible under the conditions of primitive earth.
In the second stage, biological macromolecules are produced by small organic molecules. This process takes place in the primitive ocean, that is, after long-term accumulation and interaction, small organic molecules such as amino acids and nucleotides form original protein molecules and nucleic acid molecules through condensation or polymerization under appropriate conditions (such as adsorption of clay).
In the third stage, a multi-molecular system is formed by biological macromolecules. How is this process formed? Oberlin, a scholar in the former Soviet Union, put forward the aggregate hypothesis. His experiments show that protein, polypeptide, nucleic acid and polysaccharide can be automatically concentrated and aggregated into dispersed spherical droplets when put into a suitable solution, and these droplets are aggregates. Oberlin and others believe that aggregates can show life phenomena such as synthesis, decomposition, growth and reproduction (Figure 7). For example, the aggregate has a boundary similar to a membrane, and its internal chemical characteristics are significantly different from the external solution environment. Agglomerates can absorb some molecules from the external solution as reactants, and can also undergo specific biochemical reactions under the catalysis of enzymes, and the products of the reactions can also be released from the agglomerates. In addition, some scholars have put forward other hypotheses, such as microspheres and lipid spheres, to explain the process of organic polymers forming multi-molecular systems. Fig. 7 Schematic diagram of simple metabolism of aggregates In the fourth stage, the organic multi-molecular system evolved into primitive life. This stage, formed in the primitive ocean, is the most complicated and decisive stage in the origin of life. At present, people can't verify this process in the laboratory.
3. Yu Sheng said
This hypothesis holds that the earliest life on earth or the organic matter that constitutes life came from other cosmic planets or interstellar dust. Scholars who hold this hypothesis believe that some microbial spores can attach to interstellar dust particles and fall into the earth, thus giving the earth its initial life. However, we know that the physical conditions in space, such as high-energy rays such as ultraviolet rays and temperature, are fatal to life. Even if there are these lives, they will be killed because of the high temperature when they arrive at the earth with meteorites through the atmosphere. Therefore, it seems unlikely that microbial spore-level life forms will fly from outer space. However, some scholars believe that it is entirely possible that some organic matter that constitutes life comes from space. 1On September 28th, 969, scientists discovered that a carbonaceous meteorite that fell in mcpherson Town contained 18 amino acids, of which 6 were essential for protein molecules. Scientific research shows that some organic molecules, such as amino acids, purines and pyrimidines, can be produced on the surface of interstellar dust. These organic molecules may be brought to the earth by comets or their meteorites, and primitive life may be staged on the earth.
4. Hot spring ecosystem
The origin of life may be related to the hot spring ecosystem, which has been proposed by scholars since the 1970s. In the late 1970s, scientists discovered several deep-sea hot springs near the Galapagos Islands in the eastern Pacific Ocean, where many creatures lived, including tube worms, clams and bacteria. These biomes live in high temperature (above 300℃ near the hot spring nozzle), high pressure, hypoxia, acidity and no light environment. First, these chemoautotrophic bacteria use the energy obtained from sulfide (such as H2S) ejected from hot springs to reduce CO2 to produce organic matter, and then other animals feed on these bacteria to maintain their lives. So far, scientists have discovered dozens of such deep-sea hot spring ecosystems, which are generally located near the underwater ridge formed at the junction of the two major plates of the earth.
The reason why the hot spring ecosystem is related to the origin of life is mainly based on the following facts:
(1) Most archaea found today live in an environment of high temperature, lack of oxygen, lack of sulfur and lack of acid, which is very similar to the environment near hot spring vents.
(2) The temperature near the hot spring spout is very high, and there are a lot of sulfides, CH4, H2 and CO2, which are similar to the early environment when the earth was formed.
Therefore, some scholars believe that the environment near the hot spring spout can not only provide the energy and material needed for the emergence and continuation of life, but also avoid the harmful effects caused by the impact of extraterrestrial objects on the earth, so the hot spring ecosystem is an ideal place to breed life. But other scholars believe that life may have originated on the earth's surface and then spread around deep-sea hot spring vents. The subsequent impact destroyed all life on the earth's surface, and only the creatures hidden near the deep-sea vents were preserved and multiplied. Therefore, the creatures near these vents are the common ancestors of all creatures, although they are not the earliest creatures on earth.
The mysterious origin of life
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.
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.
The origin of life can be traced back to the origin of elements and chemical molecules related to life. Therefore, the origin of life should start from the beginning of the formation of the universe. The so-called "Big Bang" produced carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur and other major elements that make up life.
About 6.6 billion years ago, there was a big explosion in the Milky Way. After a long time of gluing, its fragments and loose matter formed the solar system about 4.6 billion years ago. As a member of the solar system, the earth was also formed 4.6 billion years ago. Then, the ice-cold nebula material released a lot of gravitational potential energy, which was converted into kinetic energy and heat energy, leading to an increase in temperature, and the radioactive heat energy of the elements inside the earth also increased, so the original earth was in a molten state. In the process of high temperature earth rotation, the substances in it are differentiated, the heavy elements settle to the center and condense and nucleate, and the lighter substances constitute the mantle and crust, and gradually the circle structure appears. This process takes a long time. The original crust appeared about 3.8 billion years ago, which is consistent with the age of most rocks on the surface of the moon.
The origin and evolution of life are closely related to that of the universe. The constituent elements of life, such as carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur, come from the evolution of elements after the Big Bang. The data show that the chemical evolution in the pre-biological stage is not limited to the earth, and the products of chemical evolution exist widely in the universe. In interstellar evolution, some biomolecules, such as amino acids, purines and pyrimidines, may be formed in interstellar dust or condensed nebulae, and then under certain conditions, biopolymers such as peptides and polynucleotides are produced on the planet surface. Through several transitional forms of pre-biological evolution, the most primitive biological system, that is, life with original cell structure, was finally formed on the earth. At this point, the evolution of life began, and countless complex life forms have been produced on the earth until today.
3.8 billion years ago, a stable land mass was formed on the earth, and various evidences show that the liquid hydrosphere is hot and even boiling. Some extremely thermophilic archaea and methanogens may be closest to the oldest life forms on earth, and their metabolic patterns may be chemical and inorganic autotrophs. 3.5 billion years ago, microorganisms in the Wallavo group in Western Australia may be the earliest evidence of life on earth.
The appearance of the primitive crust marks that the earth has entered the era of geological development from the era of astronomical planets, and life with primitive cell structure has gradually formed. However, for a long time, there were not many creatures. It was not until the Cambrian 540 million years ago that a large number of metazoans with shells appeared, so the geological age after the Cambrian was called Phanerozoic.
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?
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 was 6000 years ago. Of course, it's 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 synthesis 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 reducing 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.
Through the radioactive isotope of this meteorite?