3.8 billion years ago, a stable land mass was formed on the earth, and various evidences show that the liquid hydrosphere is hot and even boiling. Some extremely thermophilic archaea and methanogens may be closest to the oldest life forms on earth, and their metabolic patterns may be chemical and inorganic autotrophs. 3.5 billion years ago, microorganisms in the Wallavo group in Western Australia may be the earliest evidence of life on earth.
The appearance of the primitive crust marks that the earth has entered the era of geological development from the era of astronomical planets, and life with primitive cell structure has gradually formed. However, for a long time, there were not many creatures. It was not until the Cambrian 540 million years ago that a large number of metazoans with shells appeared, so the geological age after the Cambrian was called Phanerozoic.
In the Middle Ages, it was also very popular in the West that God described in the Bible created everything in seven days. Today, the origin of life is not as described in these ancient legends or myths, but shows that human beings have devoted great enthusiasm and attention to the mystery of the origin of life for a long time. But how should the origin of life happen? How does science explore this eternal mystery? What progress have we made? What other problems remain unsolved?
First, the origin of life, the first mystery is the time of life, the time of origin. In the Middle Ages, people believed the story that God created man in the Bible. 1650, an Irish archbishop calculated that the exact time of God's creation was 4004 BC according to the description in the Bible, and another priest even calculated the time of creation more accurately to 9: 00 am on June 23, BC 10. That is to say, the origin of life is 6 thousand years ago, which is certainly not true, but what is it? That's a really scientific answer. How does science answer the time of the origin of life? That is to say, to answer with fossils, fossils are preserved in rocks. We know that after the death of living things, their remains are preserved in rocks under appropriate conditions. We call it a fossil. Rock formations formed in geological history, like a chronicle, are buried deep in these rocks, and older biological fossils are preserved at the bottom of the rock formations.
So far, we have found that the oldest biological fossils are rocks from western Australia, about 3.5 billion years ago. These fossils are similar to modern cyanobacteria. They are some primitive life, invisible to the naked eye. Its size is only a few microns, to dozens of microns. Therefore, we can say that life originated no later than 3.5 billion years. At the same time, we know that the earth was formed about 4.6 billion years ago. With these two data, we can see the age of the origin of life, which can be roughly defined between 4.6 billion and 3.5 billion years. Today, with the development of science, geologists believe that in the early days of the earth's formation, the earth was hit by a large number of asteroids and meteorites, which was not suitable for life. It was not so much that there was life on the earth at that time, but that it was destroying life, so the origin of life on the earth was not earlier than 4 billion years. In addition, carbon was found in 3.85 billion-year-old rocks in Greenland. As we know, there are two kinds of carbon, one is inorganic carbon and the other is organic carbon. In addition, this kind of carbon can be divided into heavy carbon and light carbon, so we can infer the source of these carbons according to the ratio of light carbon to heavy carbon in this kind of carbon. According to the isotope analysis of carbon, scientists speculate that it is organic carbon and comes from organisms. That is to say, in this way, we have greatly shortened the time of the origin of life, that is, between 4 billion and 3.8 billion years, from the origin of life on earth to the present, it is an endless evolutionary history of life.
Ok, first of all, we now have the concept of the origin of life, from 4 billion to 3.8 billion years ago. So how did life originate? Where did it originate? So we should review some hypotheses about the origin of life.
The first is creationism. In the first chapter of the Old Testament, God created everything in the world in seven days. This concept was generally accepted in the Middle Ages in the West. It can be said that this concept has been accepted by many people until now, and of course it is not established. The second is the theory of autogenesis. For example, the Greeks believed that insects were born in the soil, everything was renewed in spring, seeds sprouted from the soil, and insects broke out of the eggshells left last year. But this is not the origin of life, but the continuation of life. It can be said that this theory of autogenesis has now been completely abandoned. Similar to this statement, for example, the Egyptians believed that life came from the Nile, and there was a saying in ancient China that there were decayed grass fireflies.
The third hypothesis about the origin of life is the theory of biogenesis, which is also quite popular in the west in the19th century. The theory of student origin holds that life is inherent in the universe. If you want to ask me where life comes from, you must first answer me a question: how did the universe originate? How did this happen? You gave me an answer about how matter comes from, so I can say where life comes from. In fact, this is an agnosticism. In the second half of the 20th century, the theory of biogenesis gradually developed to the present theory of cosmic embryo species. Up to now, many scientists believe that it takes hundreds of millions of years to form enzymes necessary for life, such as protein and genetic material, and there is not enough time to complete these processes in the early earth. Because it is only 200 million years old, they think that life must have come to the earth from somewhere in the universe in the form of spores or other life. This concept also has some evidence.