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This article comes from the official account of Wechat: SF Chinese (ID:kexuejiaodian), author: SF

What is the evolution of life and what factors promote the complexity of life have always been the focus of scientists' exploration. Recently, a newly discovered microfossil provides new clues to solve these problems, which come from a critical period in Earth's history-the Great Oxidation event.

The environment of the earth has undergone many great changes, the most important of which is the Great Oxidation event (Great Oxygenation Event). This refers to a period of sudden increase in oxygen concentration on the earth about 2.4 billion years ago, which revolutionized the environment and biosphere on the earth's surface. Major oxidation events are caused by prokaryotes called cyanobacteria, which produce large amounts of oxygen through photosynthesis, which gradually accumulates in the atmosphere and oceans, forming oxygen-rich layers.

This event has had a profound impact on life on earth. On the one hand, the increase in oxygen triggered a large-scale extinction, making many anaerobic organisms (mainly archaea) unable to adapt to the oxygen-rich environment and die out; on the other hand, the increase in oxygen also creates conditions for the evolution of more complex life, because oxidation reactions can provide more energy and support more advanced cellular structures and functions.

Therefore, scientists believe that the great oxidation event promoted the leap in the complexity of life, but this hypothesis has not been supported by the fossil record. Recently, an international scientific team found a microfossil (tiny paleontological fossil) in some rocks in the Hammersley Mountains of Australia, directly confirming this hypothesis for the first time.

The new microfossils may belong to algae scientists by analyzing the chemical composition of microfossils and confirming that the carbon elements in them are produced by organisms, thus proving that these are real biological fossils. They used carbon isotopes to date and found that the age coincided with the time of the great oxidation event. They also found that these microfossils have larger and more complex cellular structures, which are significantly different from those before the great oxidation event.

Scientists eventually determined that the microfossils may belong to a kind of algae rather than simpler prokaryotes such as bacteria that existed before the great oxidation event. Algae, like all other plants and animals, are eukaryotes. In other words, they all have a membrane-wrapped nucleus in their cells, which is a more advanced form of life. On the contrary, prokaryotes have no nuclei.

So these microfossils are the first direct evidence to link changes in the environment during large oxidation events to an increase in the complexity of life. The findings, published in the journal Geobiology, provide a rare opportunity to understand the Great Oxidation event and to gain a deeper understanding of its impact on life.

Eukaryotes evolved a long time ago? The study's newsletter author, Erica Barlow, a scientist at Pennsylvania State University, discovered the microfossils during her undergraduate study. "these microfossils bear a striking resemblance to a modern creature called Characeae," she said. this suggests that this microfossil may be an early eukaryotic fossil. "

"these fossils are so well preserved that we can conduct a comprehensive study of their shape, composition and complexity," said Christopher House, a scientist at Penn State University and a co-author of the study. "these findings provide us with an excellent window into changes in the biosphere billions of years ago."

More research is needed to determine whether these microfossils are really left by eukaryotes. If these scientists' analysis is correct, it will push forward the earliest known eukaryote fossil record by nearly 750 million years. This is a very important discovery because it means that eukaryotes appeared much earlier than we previously thought.

The discovery of these microfossils also has a potential impact on our exploration of life beyond Earth, because if eukaryotes on Earth could have evolved about 2.4 billion years ago, then we have reason to believe that a similar situation may exist on other planets or moons. This means that when we look for extraterrestrial life, we should not only look for signs of prokaryotes, but also consider looking for signs of eukaryotes.

References:

Https://onlinelibrary.wiley.com/doi/full/10.1111/gbi.12576

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