According to astronomers, the earth was formed by the remains after the birth of the sun 4.6 billion years ago. It is speculated that when the earth was formed, its surface remained molten for 600 million years. The earth is heated by the core and hit by an asteroid outside, causing the temperature to rise and the water to boil into steam. After a long time, the remaining asteroids gradually settled in orbit, and asteroid impacts became less and less. At this time, various compounds of carbon, nitrogen, hydrogen and oxygen began to "synthesize amino acids and other basic compounds that constitute life." Nobel Prize winner Christian de dufour wrote in his book "Vital Dust": "These compounds are scattered on the inanimate surface of the earth with rainfall, comets and meteorites, forming a blanket of organic matter." This thin layer rich in carbon is "stirred" by the earth and celestial bodies falling on the surface of the earth, and is subjected to strong ultraviolet radiation. Due to the blocking of the earth's atmosphere, today's ultraviolet radiation is much weaker than at the beginning. These substances eventually flow into the sea. Haldane, a famous British scientist, vividly described it as "the primitive ocean turned into a pot of hot soup" in his paper 1929. The main by-products of this process are some brownish-red sticky things, which are named "sticky things" or "sticky mud"
So how did life like hot soup and a lot of ubiquitous mucus emerge from the ocean?
Because protein, nucleic acid and other biomolecules are the basis of life, they are fragile and can survive for a long time at low temperature, so chemists have always insisted that life should originate at low temperature, even in the cold environment of many degrees below zero like Jupiter's satellite. However, tiny linear fossils have been discovered near the crater, which shows that the raw materials that make up this creature should also come from near the crater. In fact, the oldest bacteria still live in craters and hot springs with temperatures as high as 1 10℃. The existence of these ancient volcanic bacteria strongly supports the theory that life originated in high temperature environment.
There are big problems in the two main research fields of exploring the origin of life. Not only is the earliest age of life pushed forward repeatedly, so that it seems that there is not enough time to carry out the chemical changes that create life, but also those chemical reactions themselves have many mysteries.
The new problem is like a dark cloud covering the picture of biological evolution, which once looked so clear on the phylogenetic tree. The phylogenetic tree was put forward by Darwin in the19th century to express the evolutionary history of fauna. The phylogenetic tree reflects the evolutionary history of organisms, and people can trace their roots along its branches. German naturalist ernst haeckel drew the first complicated phylogenetic tree, and he also coined the word "ecology". The discovery of DNA enables people to draw not only the phylogenetic tree of animals and plants, but also the genetic material that constitutes the life of animals and plants, so that we can understand the evolution process of life more deeply. In order to draw the phylogenetic tree of these systems, the researchers used comparative sequencing method. Firstly, the molecular sequence of amino acids constituting nucleic acid or protein in one organism is determined, and then it is compared with another organism. By using this technology, we can find out how far apart two fine "branches" are on a phylogenetic tree, and reveal what is the mechanism that leads to the "branches" on the phylogenetic tree (because of the evolution or mutation of organisms).
In the late 1970s, Karl Voss of the University of Illinois applied comparative sequencing to RNA molecules existing in all living things, and as a result, a much more complicated phylogenetic tree diagram was obtained than previously thought.
This phylogenetic tree has three different branches and describes three basic organisms: prokaryotes, archaea and eukaryotes. Prokaryotes are bacterial microorganisms, archaea is a new classification proposed by Voss, and it is the second group of bacterial organisms that can usually be found in very hot places such as hot springs. Eukaryotes are organisms with large cells, in which there is a nucleus separated from the surrounding environment. Eukaryotes include all multicellular organisms such as animals and plants, and of course human beings.
Since the early 1980s, as more and more genes of these three basic organisms have been decoded, problems have arisen. Except for Voss' original protein model, the racial tree patterns of these three basic organisms based on genome are all different. In addition, the phenomenon of gene duplication is surprising, which leads to the complexity of finding all gene ancestors, which shows that the original gene, that is, the gene that led to the origin of life, is quite complicated, and this complexity is not what a "starting" gene should have. The only possible explanation is to assume that in the early stage of life evolution, some genes did not always mutate to form an evolutionary tree with upward branches, but were horizontally exchanged. This theory is supported by some facts discovered now. For example, some bacteria can change some genes horizontally to make themselves more resistant to antibiotics, which is an unfortunate thing for human beings. This inference means that the tree of life has no straight trunk.
Now, experts have given different time points for the trees formed by DNA to start rising, growing and branching, from the latest 65.438 billion years ago to the previously suspected 4 billion years ago. Just like the Big Bang theory about the origin of the universe, the theory about the origin of life is also very complicated, especially with the new discovery and measurement methods promoting the improvement of knowledge. Because of this, other explanations of the origin of life that have disappeared for a long time as illusions still have loyal followers.
Will life on our earth come from space, from asteroids, meteorites, comets and even Mars? Swedish chemist Svante August areni, winner of the Nobel Prize in 1903, founded the embryology of the origin of life. He believes that bacterial spores travel in the cold universe in a dormant state, and when they meet the right planet, they begin to grow and reproduce. Areni uz didn't notice that deadly cosmic rays might kill bacterial spores. Fred Hoyle advocated another kind of more strange embryology. He believes that epidemics such as the Spanish flu epidemic in 19 18 were caused by bacteria in space, and human noses have evolved to filter out germs born in space. Francis crick (who, together with james watson and maurice wilkins, won the 1962 Nobel Prize in Physiology or Medicine for discovering the double helix structure of DNA) and Leslie Ogler, a chemical pioneer before The Origin of Life, went even further. They believe that life was "planted" on the earth by some advanced alien civilizations, and they call this assumption "the theory of directional embryology".
Perhaps in the coming 20 15 years, people will find more and even amazing evidence of life in the solar system far away from the earth. NASA probes will probe Enceladus, Saturn's moon, a planet with a frozen surface, which means there may be water below it. This probe will prove that life in the universe is more common than some conservative scientists have guessed. In recent years, we know that life on the earth exists at some extreme temperatures, and at such temperatures, we have long thought that it is extremely unfavorable to any living body. If any kind of life is found under the ice of Enceladus, embryology will be raised to a new level. At the same time, it will become more complicated for scientists to quell the debate on the origin of the universe.