Shulou(Shulou.com)11/24 Report--

In the face of more than 4 billion years of evolution history of the earth, the birth of life and the environment at the beginning of life are remote, mysterious and can not be felt intuitively. To restore the truth of the origin of life requires not only multidisciplinary cooperation, but also bold assumptions and careful verification.

The half-life of creationist radioactive elements indicates that the age of the earth is about 4.6 billion years. How on earth did biology come into being? When was it born again? This is a fascinating topic that is difficult to explain perfectly. In the ancient times when science and technology were underdeveloped, people were eager to know where all the creatures in nature came from. Was it created by God? Is it natural? Or is it evolved from other species?

Before the birth of modern science, creationism occupied an important position. At that time, human beings had no way to use scientific theory to explain the mysterious phenomena in nature, so they had to rely on the power of God.

The statue of Jesus was described in the Bible: God created the sun, moon and stars, mountains and rivers, trees and flowers, birds and beasts. Then God created Adam in his own image and used one of Adam's ribs to create Eve.

An important feature of the creationism of Adam and Eve on the dyed glass of Notre Dame, France: all the species that have been created will not change again, and even if there is a change, there will be some changes in a very small range. without becoming another species.

In the era of undeveloped science and technology, human beings lack the most basic understanding of the world in front of them. in order to be able to explain natural phenomena, people can only fantasize boldly.

Naturally occurring mice in the technologically underdeveloped ancient times, there were many ridiculous claims about the origin of life, but these views influenced academia for many years, including scientific giants such as Aristotle and Newton.

At that time, there was a theory of natural occurrence, and its core view was that life, especially simple life, occurs naturally by inanimate matter.

The first person to support the theory of natural occurrence was Aristotle. Aristotle believed that matter occurred naturally and even compiled a list of the sources of all kinds of matter.

He believes that the reproduction of every substance needs "heat". Higher animals are produced through "animal fever", while lower animals are produced from mucus and soil under the combined action of Rain Water, air and solar heat.

At that time, these views were regarded as universal truths. Newton also stood up for the theory of natural occurrence, believing that plants were formed by the tails of weakening comets.

Many scientists support the theory of natural occurrence. Famous scientist Helmont once proposed: put chaff and rags into a bottle, put the bottle under the bed will give birth to mice.

Helmont was a famous chemist and philosopher in the 17th century. he was an important figure in the process of guiding alchemy to chemistry, and he was also the first person to discover carbon dioxide. He believes that when wood and other substances are burned, they get wild gas, which is what we often call carbon dioxide.

Helmont's work on chemistry was groundbreaking, but he stumbled on the theory of biological spontaneity. However, we should put these arguments under the historical conditions at that time. In ancient times, when science and technology were extremely backward, we were able to think deeply and put forward such a point of view, which also contributed to a certain extent.

There is also a chemical origin hypothesis about the origin of life in primitive soup.

The main content of this hypothesis is that the birth of life has gone through two main stages: in the first stage, early chemical reactions took place in the primitive atmosphere and ocean, forming the most primitive organic and biological macromolecular systems; in the second stage, these macromolecules form primitive life.

The primitive earth ocean in the chemical origin hypothesis is full of various uncertain factors, in which there are various conditions for the occurrence of chemical reactions, as well as a large number of small molecular substances, just like a pot of "primitive soup" for the birth of life.

The theory of "primitive soup" was jointly put forward by Soviet biochemist Alexander Ivanovich Oblin (Oparin, Alexander Ivanovich) and Indian biologist Haldane. The "primitive soup" experiment, which we often talk about, was created by Oblin.

The Picture of the primitive Ocean Oblin published the Origin of Life on Earth in 1936, in which he put forward a hypothesis about the origin of life. He believes that in the primitive earth atmosphere, there are a large number of cosmic rays, ultraviolet rays, lightning and other energy sources that contain a lot of energy. under their action, CO2, N2, H2S, H2 and NH3 in the primitive atmosphere continue to polymerize to form small molecular compounds, such as amino acids, purines, pyrimidines, ribose, etc., which are the basic components of macromolecular life matter.

The primitive earth is like a reaction container, the internal volcanoes continue to erupt, the temperature is very high, many gases brought by volcanic eruptions, including CH4, NH3, HCN, H2S, CO2 and so on, form the primitive atmosphere. Under the action of intense ultraviolet, cosmic rays, high-energy particle flow, lightning and other energy, various small molecular compounds are synthesized.

In order to further verify the correctness of the hypothesis, scientists try to simulate the atmospheric and marine environment of the primitive earth to see if inorganic matter can be synthesized into simple basic substances of life, including nucleic acid and protein precursors: amino acids, peptides, nucleotides.

Arginine in amino acids in 1953, Miller, a graduate student at the University of Chicago in the United States, under the guidance of his mentor, injected water into a 500ml flask, and at the same time sucked the air out of the glass bottle, adding a mixture of CH4, NH3, H2 and other gases that simulated the reductive atmosphere of the primitive earth.

In the experiment, he continued to heat the flask, allowing water vapor and a mixture of gases from the simulated original atmosphere to enter another flask with a capacity of 5 liters through an airtight pipe, and then simulated lightning in the original atmosphere by electric spark discharge.

A week later, the team examined the solution gathered at the bottom of the container to see if there were any simple substances, which were equivalent to the primitive ocean formed by Rain Water.

The results showed that there were 20 kinds of organic compounds in these discharge cooled solutions, including 11 kinds of amino acids, and 4 of these 11 kinds of amino acids were essential amino acids for human body. They are glycine, alanine, aspartic acid and glutamic acid, respectively.

The result of Blue Lightning confirms the validity of the hypothesis of Oblin and Haldane. Miller made some changes to the composition of the reductive atmosphere in the hypothesis. He believed that the main components of the reductive atmosphere in the primitive earth should be CH4, N2, as well as trace amounts of NH3 and H2O, because a large amount of NH3 would be directly dissolved in water.

Then Miller and his colleagues did a large number of experiments, using ultraviolet, β-ray and high temperature as energy sources respectively, while changing the composition of the mixed gas, for example, using H2S instead of H2O and HCN instead of CH4. The experimental results show that they can produce small molecules of amino acids. After the production of small molecules of amino acids, the origin of life has the most basic raw materials.

There is also a popular view that gifts from outer space: life originated in outer space, also known as the "universal provenance hypothesis" or "cosmic embryo provenance hypothesis".

In 1907, Swedish chemist Swanter Auguste Alenius (Svante AugustArrhenius) first put forward the "cosmic embryo provenance hypothesis". He put forward such a view: there are a large number of "life embryo" floating in the vast space, and "life embryo" is the most primitive form of life, which can develop and give birth to life.

Meteorites in outer space float around in space with the action of external forces such as solar wind and black hole pressure. There is an opportunity to land on the surface of some planets with meteorites, comets, interstellar dust and so on. If the planet happens to have the right conditions for life, then the most primitive life will be born. In this way, the "embryo of life" in outer space spreads from one planet to another. And life on Earth happens to come from the "embryo of life" in outer space, creating a prosperous and diverse species on Earth.

This theory is supported by many scientists, including National Aeronautics andSpace Administration, NASA astrophysicists, who believe that life on Earth probably originated from comets that crashed into the ocean 4 billion years ago.

There are also many meteorites on Earth, one of the most widely studied is the meteorite named "Murchison" that crashed in the Australian town of Merchison in 1969.

The meteorite contains more than 70 amino acids, including glycine, glutamic acid and alanine, as well as two nucleic acid molecules that make up life: uracil and xanthine. Radiocarbon dating analysis confirmed that these molecules were formed in outer space, providing the most direct evidence for the "cosmic embryo provenance hypothesis".

The hypothesis of meteorites in space has some problems that are difficult to explain. For example, in outer space, there are very destructive rays, such as ultraviolet rays, which are highly lethal to living substances, including the so-called "embryo of life", so how did these primitive living substances survive? In addition, in the process of entering the earth, we have to go through a series of tests of high temperature, high heat and harsh environment, and the living environment of the earth at that time is unknown. Can these simple protein or nucleic acid molecules remain active in such an environment?

This claim has yet to be further confirmed.

In the abyss of poison and heat, there is another hypothesis about the origin of life that has been accepted by more people. This hypothesis holds that life should have originated at the bottom of the primitive ocean.

In 1979, many vents braving black solution were found at the bottom of the Pacific Ocean at a depth of 2000 meters. The black solution forms a unique column after it is cooled by cold sea water. There are many primitive microbial communities near the column, including thiophilic bacteria, archaea and so on. They can obtain energy by oxidizing sulfur ion, manganese ion, ferrous ion and other substances, and convert inorganic carbon into organic carbon. The mineral elements gushing from the seafloor also provide nutrients for the reproduction and growth of these bacteria, forming a special ecosystem.

The temperature of the liquid ejected from the submarine crater is as high as 350C and contains small molecules such as H2S, CH4 and CN, which provides conditions for abiotic organic synthesis. These chemoautotrophic bacteria can use the energy from sulfides ejected from hot springs to reduce CO2 to produce organic matter.

Geological studies have shown that the environmental conditions near seafloor hydrothermal vents are very similar to those of the primitive earth, so many scientists speculate that primitive life probably originated in the hydrothermal environment of the seafloor. not the original atmosphere. There are a large number of reducing substances in such an environment, which can provide energy by oxidizing these reducing substances, and then gradually turn inorganic matter into organic matter, and then synthesize macromolecules from small molecules, and then gradually give birth to life.

This hypothesis is supported by the results of genome sequencing and geological research. Carl Woese, a researcher at the University of Illinois in the United States, analyzed the genome sequence of bacteria from the seafloor hydrothermal mouth and concluded that these bacteria are the simplest and oldest archaea prokaryotes, and their juxtaposition into the third realm with true bacteria and eukaryotes is enough to explain its ancient history.

In 1996, researchers at the American Institute of Genomics also analyzed the genome of a methanogenic bacterium at the bottom of the Pacific Ocean and deciphered 1700 genetic codes. it is determined that this kind of archaea is a third branch different from true bacteria and eukaryotes, and is older from the point of view of origin, thus inferred that these archaea are the earliest forms of primitive life.

In addition, geological evidence indirectly supports this hypothesis. Traces left over from life activities will be preserved on ancient rocks that have not undergone metamorphism, which is also an important basis for exploring the origin of life in geology.

In 1997, a rock thought to be extremely ancient was discovered in the Ita area of Greenland. It has been analyzed for 3.85 billion years and is the oldest marine sediment ever discovered. There are obvious traces of biological activity in the rocks, and the traces of life activity in such an ancient age also indirectly indicate that life originated from archaea at the bottom of the primitive ocean.

After the hypothesis that methanosarcina is an archaea was put forward, it has also been questioned by many people. For example, some people think that the high temperature near the seafloor will promote the chemical reaction, but the high temperature is also extremely destructive to the proteins that make up life; the life span of the black columnar complex is very short, only a few decades, and life cannot be born in such a short time, and the surrounding environment is too acidic, the pH value is 1: 2, which is not conducive to the birth of life; and so on.

Under the "contention of a hundred schools of thought" about the origin of life, there have been several influential scientific debates.

The first time is between the theory of natural occurrence and the theory of origin. The theory of biogeny is relative to the theory of natural occurrence, which is put forward by French biologist LouisPasteur, that is, organisms can not occur naturally, they can only be produced through biological reproduction. In the end, Pasteur provided conclusive evidence through a series of precise experiments to declare the complete victory of the theory of origin.

The second debate is the debate between the cosmic embryo provenance hypothesis and the chemical origin hypothesis. Because ultraviolet rays and cosmic rays that exist widely in outer space have a strong killing effect on life matter, the chemical origin hypothesis prevails.

The protagonist of the third debate is also these two theories. The origin theory of primitive surface chemistry represented by Oblin theory has basically matured and spread rapidly, along with the rapid development of radio astronomy and cosmic chemistry. A large number of organic matter in the universe have been discovered, and the cosmic embryo provenance hypothesis has gained the upper hand.

In the face of different hypotheses about the origin of life, the truth of the origin of life is still unknown and needs to be further studied.

Author: Liu Rui

Source: "telling teenagers about Life Science"

Editor: Zhang Runxin

This article comes from the official account of Wechat: Origin Reading (ID:tupydread), author: Liu Rui

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