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 and phosphoric acid, etc. Under the action of various natural energy sources (such as lightning, ultraviolet rays, cosmic rays and volcanic eruptions, etc.). ). Into biological monomers (such as amino acids, sugars, adenosine and nucleotides, etc. ). These biological monomers are further polymerized into biopolymers, such as protein, polysaccharides and nucleic acids. This process is called chemical evolution. After protein appeared, the simplest life was born. This is a major event that happened about 3.6 billion years ago. Since then, there has been life on the earth. The most basic difference between living things and non-living things is that it can absorb substances needed in its own life process from the environment and expel substances that are not needed in its own life process. This process is called metabolism, which is the first difference. The second difference is that it 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. They can pass on 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. This difference from the previous generation is called variation. If this characteristic can adapt to the environment and survive, it will strengthen this characteristic of generational variation and become the inherent characteristic of new individuals. Organisms are constantly mutating, inheriting and aging for a long time, and new individuals with new characteristics are constantly appearing, which makes organisms constantly change from simple to complex, which constitutes the systematic evolution of organisms.

Forms 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 depends on the cell surface to absorb nutrients directly from the surrounding environment to maintain life. This lifestyle is called heterotrophy. At that time, their living environment was short of oxygen. This kind of life that likes to live in an anoxic environment is called anaerobic. So the earliest prokaryotes were heterotrophic and anaerobic. Its shape is spherical at first, then it becomes oval, arc, glutinous rice strip and then spiral and slender. 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, not only the oxygen content in water has been high, but also the oxygen content in the atmosphere has been quite high. The appearance of nucleus is a great event in the evolution of biology. After more than 654.38+0.5 billion years of evolution, prokaryotic plants were covered with a membrane after the nuclear substances that were originally uniformly dispersed in their cells were relatively concentrated. This membrane is called the 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 inside the cell is formed. Organisms with nuclei are called eukaryotes. Since then, cells are no longer simply divided into two cytoplasm in the process of reproduction and division, and the nucleus inside is also divided into two. Eukaryotes (there were no animals at that time, it can be said that they were actually just eukaryotic plants) appeared about 2 billion years ago. The emergence of gender is another important event in the evolution of biology, because gender promotes the eugenics of biology and accelerates the development of biology in a more complicated direction. Therefore, eukaryotic multicellular plants appeared hundreds of millions of years after eukaryotic unicellular plants appeared. The division of labor of plants appeared shortly after the emergence of eukaryotic multicellular plants. There is a group of cells in plants, whose main function is to fix plants and become fixed organs. This is the origin of modern algae plant fixators. Since then, organ differentiation has begun, and the internal cell morphology of different functional parts has also begun 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, people have made a comprehensive study on the origin of life on the basis of new achievements in modern natural science, and made great progress.

According to scientific calculations, the earth has a history of about 4.6 billion years since its birth. In the early days, the earth was hot, and all the elements on the earth were gaseous. There was absolutely no life at that time. The initial life gradually evolved from inanimate matter through extremely complicated chemical processes after the earth's temperature dropped. At present, it has been widely accepted by scholars that the origin of life is through the process of chemical evolution.

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 the imagination of primitive earth.

(left) primitive atmosphere (right) organic matter formation

(NH3), water vapor (H2O), hydrogen (H2), and 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, when the earth's temperature drops further, these small organic molecules will flow with the rain.

This speculation has been confirmed by scientific experiments. 1935, American scholar Miller and others designed a set of sealing devices (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 simulate the lightning under the condition of primitive earth, and continue to carry out spark discharge. 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 generation of amino acids on earth.

In addition, some scholars have simulated the atmospheric composition of the primitive earth and made other organic substances in the laboratory, such as purine, pyrimidine, ribose, deoxyribose, fatty acids and so on. These studies show that the chemical process of synthesizing organic matter from inorganic substances is completely possible in the origin of life.

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 have simulated the conditions of the primitive earth and made substances similar to protein and nucleic acid. Although these substances are still different from 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. It is possible to produce these organic polymers under primitive earth conditions.

Judging from the multi-molecular system composed of organic polymers, protein, nucleic acid and other organic polymers are accumulating more and more in the ocean, with higher and higher concentrations. 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 bread is separated from the surrounding primitive marine environment, thus forming an independent system.

It is the most complicated and decisive stage in the origin of life, 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 large sub-systems have evolved continuously for a long time, especially due to the interaction between protein and nucleic acid, and finally formed primitive life with primitive metabolism and reproduction. Later, by.

Although a large number of simulation experiments have been carried out on the chemical evolution process of the origin of life, most of the experiments are only focused on the first stage, and some stages are limited to assumptions and speculations. 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. In 2008+0965, scientists in China synthesized crystalline bovine insulin (a protein containing 5 1 amino acid). In 2008+098 1 year, China scientists also synthesized yeast alanine transport ribonucleic acid (a kind of ribonucleic acid) by artificial method. 48866.8686888686 1