And it is composed of basic biological macromolecules, which are formed by inorganic molecules in nature under certain conditions and then developed. Since then, there has been life on the earth. The following is a detailed introduction:
The mysterious origin of life
About 5 billion years ago, the primitive solar system was formed by the slowly rotating gas and dust clouds in the universe. By 4.7 billion years ago, some gas and dust clouds in the primitive solar system condensed to form the original earth. The newborn earth is very cold and desolate. Without complex materials, there would certainly be no life. Life begins with the birth of primitive atmosphere.
In the early solar system, some primitive celestial bodies frequently collided with the young earth, which on the one hand increased the volume of the earth, on the other hand converted the energy of motion into heat energy and stored it in the earth. Collisions keep happening, and a lot of heat energy accumulates in the earth. The average temperature of the earth is as high as several thousand degrees Celsius, and the metals and minerals in it have turned into fiery magma. Magma moves violently inside the earth and rushes out of the surface from time to time, forming a volcanic eruption. On the primitive earth, volcanic eruptions were very frequent. With the eruption of volcanoes, some gases in the earth are constantly released, forming a primitive atmosphere. However, there are still no biomolecules on the earth at this time.
In later years, due to the accumulation of water vapor in the primitive atmosphere, the surface temperature of the earth began to decrease. When it drops below the boiling point of water, water vapor turns into downpour and falls to the ground. It rained day and night, forming the initial ocean and preparing the cradle for the birth of life.
At that time, the temperature of the earth's surface was still very high. By about 3.6 billion years ago, the temperature of seawater had dropped to about 80℃, but before that, primitive life had been quietly bred.
The birth of life is closely related to the primitive atmosphere. It is speculated that the main components of the primitive atmosphere are carbon monoxide, carbon dioxide, methane, water vapor and ammonia. If these simple gas molecules want to become biomolecules, they must become complex enough. It takes energy to synthesize complex substances.
Fortunately, there are various forms of energy available on the primitive earth. First of all, there is no ozone layer in the primitive atmosphere, and ultraviolet rays in sunlight can enter the atmosphere unscrupulously, bringing energy to the earth. Secondly, lightning will appear in the primitive atmosphere, which is a phenomenon of energy release. Thirdly, there are frequent volcanic activities on the primitive earth, and volcanic eruption can release a lot of heat.
After absorbing energy, simple gas molecules will become extremely active, and then produce chemical reactions to form complex (living) substances. Miller, an American scientist, was the first scientist to successfully synthesize complex (living) substances by simulating the atmospheric conditions of the primitive earth.
Episode 2 How was life born?
Miller designed a set of glass instruments. The spherical glass container simulates the primitive earth's atmosphere, mainly including hydrogen, methane and ammonia. During the experiment, the water in the flask needs to be boiled to simulate the evaporation phenomenon in the primitive ocean. The spherical spark chamber is connected with a high-frequency coil to make the electrode discharge continuously, simulating the discharge phenomenon in the primitive earth atmosphere. The discharge lasted for a week. To Miller's surprise, a variety of amino acids were produced in the experiment.
Amino acids and nucleotides are the two most common and important biological small molecules in animals and plants. They are the bricks and stones that build the building of life.
It is undoubtedly a key step in the evolution of life to change from small inorganic molecules that are not the basic structural units of organisms to small biological molecules. However, because small biological molecules are too simple after all, only after they have evolved into more complex biological macromolecules can life be born.
On the primitive earth, naturally synthesized amino acids and nucleotides are collected in lakes and oceans with rainwater. Mineral clay will adsorb these small biomolecules around it. Under the catalysis of metal ions such as copper, zinc, sodium and magnesium, many amino acid molecules are linked together by removing water molecules, forming more complex molecules, namely protein molecules. Similarly, many nucleotide molecules can be linked together by removing water molecules to form more complex molecules, namely nucleic acid molecules.
Nucleic acid is the genetic material of organisms, and the information of growth, reproduction, behavior and metabolism of organisms is contained in the nucleotide sequence of nucleic acid molecules. It can be said that every nucleotide sequence is an article that records life information, and the words written are nucleotides. Nucleic acid is the information molecule of life, which is absolutely important to life. The function of nucleic acid is realized by protein, and even the replication of nucleic acid itself needs protein's participation.
After the appearance of nucleic acid and protein in the lakes and oceans of the primitive earth, some people may think that life was born, because some viruses in nature are composed of nucleic acid and protein, and the viroid is pitifully simple, just a nucleic acid molecule, which can invade plant cells and make plants sick. Potato spindle tuber disease is the result of this virus-like infection.
Viruses and viroids can only survive and reproduce in living cells, and whether they are a life form is still controversial.
In order to adapt to the environment, in the process of evolution, organisms must evolve from simple to complex, from low to high. However, a simple molecule is unable to gather other substances around itself in the process of reproduction, and it must form a complex entity with a certain structure.
In the primitive ocean, with the passage of time, the concentration of naturally synthesized biological macromolecules is getting higher and higher, and finally a molecular entity with a certain morphological structure is formed, which further evolves into the most primitive life.
Episode III Evolution of Genetic Material
As we all know, nucleic acid is the genetic material of all living things on earth today. It carries life information and can replicate itself. There are two kinds of nucleic acids: one is ribonucleic acid, also called RNA. In RNA viruses and viroids, RNA carries all life information; The other is deoxyribonucleic acid, also called DNA, which is the genetic material of most organisms at present.
There are indications that the first complex molecule on the primitive earth may be RNA. Why do you say that?
First of all, RNA molecules are relatively simple, with only one chain, while DNA molecules are very complex, with two chains. According to the law of evolution, simple molecules always appear first. Secondly, the self-replication of DNA molecules is inseparable from enzymes. The essence of enzyme is protein. On the primitive earth, before protein came into being, DNA molecules could not replicate themselves. However, some RNA molecules themselves have enzymatic activity. Under primitive earth conditions, RNA can replicate itself even without protein.
In the Origin of Life, the theory that RNA first appeared can be accepted by more scholars in the scientific community. However, there are still many problems to prove that RNA is the earliest genetic material. The biggest problem is that it is very difficult to synthesize RNA under simulated original conditions.
For a long time, people have always thought that only nucleic acid is genetic material. In recent years, biologists have found that the pathogen of mad cow disease and mad sheep disease is prion, and the essence of prion is protein, and protein can replicate itself, which inspires people that protein can also be used as genetic material.
In fact, like nucleic acids, protein has a regular molecular structure and helical structure. After long-term research, scientists have found that protein is fully equipped with genetic materials, which can store, copy and transmit life information.
As we all know, protein is composed of amino acids. By pairing amino acids, genetic information can be passed on to the next generation.
Through experiments, researcher Liu Ciquan put forward a pairing model of amino acids, and drew a very distinctive genetic code table on this basis.
On the primitive earth, the earliest self-replicating molecule may be protein. At that time, protein could not only store or transmit genetic information, but also perform specific biological functions.
For primitive life, this characteristic of protein is very economical. Later, with the evolution of life, protein handed over the function of storing or transmitting genetic information to RNA. However, RNA is not stable enough. With the continuous evolution of life, DNA appeared again, and DNA is the genetic material that appeared later.
The advantages of DNA as genetic material are as follows: firstly, compared with RNA, some parts of DNA lack oxygen atoms, which are very active, making DNA more stable and better preserving life information; Secondly, RNA is single-stranded, and if it is destroyed, life information will be lost, while DNA is double-stranded. After a chain is damaged, it can be repaired according to another chain, so life information is not easy to be lost.
Therefore, today's life on earth chooses DNA as genetic material, which is also the result of long-term evolution of natural organisms.
However, before the discovery of extraterrestrial life, it is uncertain whether life on earth is accidental or inevitable.
My answer should be the standard answer, the landlord will see if it is!