The earth where we live is full of life. So far, there are more than 6.5438+0.4 million known species in the world, and many new species have not been discovered. Scientists estimate that there are about 6.5438+million to 30 million species of life on the whole earth. Surprisingly, these huge and diverse species all evolved from the same ancestor. So, when was this oldest ancestor born and how did it develop?
To answer this question, the most important evidence is fossils. At present, the oldest fossil known to mankind is the primitive bacteria found in Australia, which lived about 3.5 billion years ago. It is speculated that the ancestor of life may have appeared 3.5 billion years ago.
4 billion years ago, a primitive ocean was formed on the earth. At that time, the temperature of the sea water was very high. With the gradual decline of water temperature, the birth of life has the necessary external conditions.
However, the situation in the atmosphere is still very bad, and there is almost no oxygen in the air. In this way, the earliest primitive life can only be an anaerobic creature that does not need oxygen. Moreover, due to lack of oxygen, the ozone layer cannot be formed over the earth, and ultraviolet rays kill all the way, threatening fragile life, so primitive life has to live in the sea more than ten meters or even dozens of meters deep.
With the slow development of biology, blue-green algae appeared 2.6 billion years ago. This algae has chlorophyll, which can produce oxygen through photosynthesis. Therefore, single-celled organisms adapted to aerobic environment have stepped onto the historical stage. At that time, most oxygen combined with iron in seawater to form iron oxide, thus forming iron ore deposits all over the world today. This resource supports 70% of the iron demand in today's society, which can be regarded as a great legacy left by the earth in ancient times to our modern human beings.
People who know some genetic laws may ask that the continuation of life is carried out through the information of DNA genetic code given by the previous generation. In that case, who gave the genetic code of the first life?
Many scientists have done a lot of research on this, among which American chemists Leo and Miller designed a very famous experiment to try to solve this mystery. They filled the flask with water and various atmospheric components, such as ammonia, methane and hydrogen. In the primitive earth period, lightning was simulated in the form of discharge. A week later, organic molecules such as formic acid, acetic acid and lactic acid were produced in the flask, as well as amino acids such as glycine and propiolic acid, which constitute protein. Obviously, natural phenomena such as lightning can produce molecules that form life, but the development from molecules to primitive life is undoubtedly an extremely long process, and it is impossible to get results with a simple experiment. But in any case, the experiment brought the possible trajectory of life development and laid the foundation for further research.
Life developed to1.600 million years ago, and multicellular organisms formed. Since then, life has evolved faster and faster. About 700 million years ago, marine invertebrates that could be distinguished by the naked eye appeared and multiplied rapidly. Australia's famous Ediacara biota is the product of this period.
About 570 million years ago, organisms developed a hard tissue structure, which is obviously different from soft tissue organisms. They are easy to become fossils. Therefore, the fossil records around the world have increased rapidly since this period, which is called the beginning of CAMBRIAN in geology.
The arrival of CAMBRIAN marks the rapid diversification of organisms, so this period is also called the period of life explosion. The representative organisms of many classes that we can list in the world today can be found in the fossils of this period.