The origin of life is the latest.

After the earth was formed in the universe, there was no life at first. After long-term chemical evolution, that is to say, organic elements in the atmosphere, such as hydrogen, carbon, nitrogen, oxygen, sulfur, phosphorus, etc., are synthesized into organic molecules (such as methane, carbon dioxide, carbon monoxide, water, hydrogen sulfide, ammonia, phosphoric acid, etc. Under the action of various natural energy sources (such as lightning, ultraviolet rays, cosmic rays and volcanic eruptions, etc.). These organic molecules are further synthesized and become biological monomers (such as amino acids, sugars, adenosine, nucleotides). These biological monomers are further polymerized into biopolymers. Such as protein, polysaccharide, nucleic acid, etc. This process is called chemical evolution. After protein appeared, the simplest life was born. This is a great event that happened about 3.6 billion years ago. Since then, there has been life on the earth. The most basic difference between biological and abiotic substances is that it can absorb substances needed in its own life process from the environment and expel substances unnecessary in its own life process. This process is called metabolism, which is the first difference. The second difference is that you can reproduce. Any living individual, no matter how different their reproductive forms are, has the ability to reproduce new individuals. The third difference is the ability to inherit. It can transfer the characteristics of the previous generation to the next generation, so that the new individuals of the next generation can have the same or roughly the same characteristics as the previous generation. This roughly the same phenomenon is the most meaningful and worthy of our attention. Because it shows that it is a little different from the previous generation, which is called variation. If this variation can adapt to the environment and survive, it will be strengthened from generation to generation and become the inherent characteristics of new individuals. Organisms are constantly mutating and inheriting, and after a long time, new individuals with new characteristics appear constantly, which makes organisms change from simple to complex and constitutes the systematic evolution of organisms.

Morphology and characteristics of early life on earth. The earliest life form on earth is very simple. A cell is an individual. It has no nucleus. We call it prokaryote. It survives by directly absorbing nutrients from the surrounding environment on the cell surface. This lifestyle is called heterotrophy. At that time, their living environment was anoxic, which was called anaerobic. So the earliest prokaryotes were heterotrophic and anaerobic. Its shape is spherical at first, then it becomes oval, arc, sticky rice strip, then it becomes spiral, slender and filiform, and so on. From the development direction of morphological changes, it is to increase the surface area of the body in contact with the outside world and increase its own volume. Bacteria and cyanobacteria living on the earth now belong to prokaryotes. The occurrence and development of cyanobacteria has accelerated the increase of oxygen content on the earth. Since more than 2 billion years ago, there has been a large amount of oxygen not only in water but also in the atmosphere. The appearance of nucleus is an important event in biological evolution. Prokaryotes have evolved for/kloc-0.5 billion years. The nuclear substances that were originally dispersed uniformly in their cells are relatively concentrated and covered with a membrane called nuclear membrane. The nuclear membrane of a cell separates the nuclear matter in the membrane from the cytoplasm outside the membrane. This is how the nucleus of a cell is formed. Organisms with nuclei are called eukaryotes. Since then, cells are no longer simply divided into two cytoplasm during reproduction and division, and the nucleus inside is also divided into two. Eukaryotes (there were no animals at that time, so to speak, they were actually just eukaryotic plants) appeared about 2 billion years ago. The emergence of gender is another important event in the process of biological evolution, because gender promotes the eugenics of biology and accelerates the development of biology in a more complicated direction. Therefore, after the appearance of eukaryotic unicellular plants, it took hundreds of millions of years for eukaryotic multicellular plants to appear. Not long after the appearance of eukaryotic multicellular plants, the division of labor of plants appeared. A group of cells in plants mainly play the role of fixing plants and become fixed organs, which is the origin of modern algae plant fixators. From then on, organ differentiation began to appear, and the internal cell morphology of different functional parts also began to differentiate. It can be seen that the appearance of nucleus and sex has greatly accelerated the development of the morphology and function of the organism itself.

The origin of life

For a long time, there are various explanations about the origin of life. In recent decades, according to the new achievements of modern natural science, people have made a comprehensive study on the origin of life and made great progress.

According to scientific calculations, the earth has a history of about 4.6 billion years since its birth. The early earth was very hot, and all the elements on the earth were in a gaseous state. At that time, there would never be life. The initial life evolved step by step from inanimate matter through extremely complicated chemical processes in an extremely long time after the earth's temperature dropped. At present, this view that the origin of life is through the chemical evolution process has been recognized by most scholars, and that this chemical evolution process can be divided into the following four stages.

It is speculated that the chemical evolution of the origin of life began under the conditions of the primitive earth. At that time, the surface temperature of the earth had dropped, but the internal temperature was still very high and volcanic activity was extremely frequent. The gas ejected from the volcano formed the primitive atmosphere (below). It is generally believed that the main components of primitive atmosphere are methane (CH4) and ammonia, which is an imaginary map of primitive earth.

(left) primitive atmosphere (right) organic matter formation

(NH3), water vapor (H2O), hydrogen (H2), in addition to hydrogen sulfide (H2S) and hydrogen cyanide (HCN). Under the action of cosmic rays, ultraviolet rays and lightning, these gases may naturally synthesize a series of relatively simple organic small molecules such as amino acids, nucleotides and monosaccharides. Later, the earth's temperature dropped further, and these small organic molecules flowed through lakes and rivers with the rain, and final gathering was in the primitive ocean.

This speculation has been confirmed by scientific experiments. 1935, American scholar Miller and others designed a set of sealing device (below). They pumped the air out of the device, then simulated the atmospheric composition on the primitive earth and introduced methane, ammonia, hydrogen and water into the Miller experimental device.

Steam and other gases, and simulated lightning and continuous spark discharge under primitive earth conditions. Finally, amino acids were detected in the U-tube. Amino acid is the basic unit of protein, so it is of great significance to explore the production of amino acids on earth.

In addition, some scholars simulate the atmospheric composition of the primitive earth and make other organic substances in the laboratory, such as purine, pyrimidine, ribose, deoxyribose, fatty acids and so on. These studies show that in the Origin of Life, the chemical process of inorganic synthesis of organic matter is completely possible.

How were organic polymers such as protein and nucleic acid formed by small organic molecules formed under primitive earth conditions? Some scholars believe that in the primitive ocean, small organic molecules such as amino acids and nucleotides, after long-term accumulation and interaction, formed primitive protein molecules and nucleic acid molecules through condensation or polymerization under appropriate conditions (such as adsorption on clay).

Now, some people imitate the conditions of primitive earth and make substances similar to protein and nucleic acid. Although there are some differences between these substances and protein and nucleic acid, it is not certain whether the formation process of protein and nucleic acid on the primitive earth is like this, but it has provided some clues for people to study the origin of life; Under the conditions of primitive earth, it is possible to produce these organic polymers.

According to the multi-molecular system composed of organic polymers, it is speculated that protein, nucleic acid and other organic polymers accumulate more and more in the ocean, and the concentration keeps increasing. Due to various reasons (such as evaporation of water and adsorption of clay), these organic polymers are concentrated and separated, and they interact and condense into droplets. These droplets float in the primitive ocean, and the outer layer has the most primitive boundary film, which is isolated from the surrounding primitive marine environment, thus forming an independent system, that is, a multi-molecular system. This multi-molecular system has been able to carry out primitive material exchange activities with the external environment.

The evolution from multi-molecular system to primitive life and from multi-molecular system to primitive life is the most complex and decisive stage in the process of life origin, which directly involves the occurrence of primitive life. At present, people can't verify this process in the laboratory. However, we can speculate that some multi-molecular systems have evolved for a long time, especially the interaction between protein and nucleic acid, and finally formed primitive life with primitive metabolism and reproduction. Later, from the chemical evolution stage of the origin of life to the biological evolution stage after the emergence of life.

Although a large number of simulation experiments have been carried out on the chemical evolution process of the origin of life, most of them are only concentrated in the first stage, and some stages are limited to hypothesis and speculation. Therefore, we must continue to study and discuss the origin of life.

Protein and nucleic acid are the most important substances in organisms. Without protein and nucleic acid, there would be no life. 1965, China scientists synthesized crystalline bovine insulin (a protein containing 5 1 amino acid). 198 1 year, China scientists synthesized yeast alanine transport ribonucleic acid (a kind of ribonucleic acid) artificially. These works reflect China's great achievements in exploring the origin of life.