An international team of scientists from Wales, France and China has discovered new evidence that relatively complex life forms may have originated on Earth 1,5 billion years ago, nearly four times earlier than currently believed by the scientific community.
The team working in Gabon states that deep in the rocks they discovered evidence that the conditions for the existence of animal life existed 2,1 billion years ago, during the Paleoproterozoic period.
They believe that there was a shallow subterranean sea densely populated with living creatures, similar to single-celled mold that reproduces by spores.
However, as far as the fossils can tell, the strange organisms never spread beyond the underground reservoir - and eventually died there.
These assumptions are quite different from conventional thinking and not all scientists agree with this new theory.
Most experts believe that life on Earth originated about 635 million years ago.
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The research adds to the ongoing debate about whether the formations found in Gabon are actually fossils.
Scientists have analyzed the rocks around the formations to see if there is evidence that they contain elements like oxygen and sulfur that would allow life to exist.
Professor Ernest Chi Fru, from Cardiff University, worked with an international team of scientists.
He told the BBC that if his theory is correct, these life forms could be similar to slime mold - single-celled organisms without a nervous system that reproduce by spores.
However, Professor Graham Shields from University College London, who was not involved in the research, has some doubts.
"I'm not opposed to the idea that 2,1 billion years ago there were more nutrients, but I'm not sure it could have led to complex life," he says, suggesting more evidence is needed.
However, Professor Chi Fru is convinced that his team's research has helped to prove an alternative theory about the beginning of evolution and the origin of the first life on Earth.
"We say - look, these are fossils, there is oxygen, it encouraged the appearance of the first complex living organisms.
"We see the same processes as in the Cambrian period 635 million years ago. It helps us finally understand where we all came from," he says.
The first hint that complex life arose earlier than thought appeared ten years ago when the so-called Fransvillian formations were discovered.
Professor Chi Fru and his colleagues said the formations were made of fossils, indicating the existence of a life form that could "squirm" and move on its own.
These discoveries were not accepted by all scientists.
To find more evidence for this theory, Chi Fru and his team have now analyzed rock cores from Gabon.
The composition of the rocks showed that the "laboratory" in which life could exist was created immediately before the appearance of the formations.
They believe that the high levels of oxygen and sulfur were created after the collision of two continental plates under the water, which caused volcanic activity.
The collision of the plates separated part of the sea from the ocean, creating a "shallow sea surrounded by land that is rich in nutrients".
Chi Fru says that the conditions for photosynthesis existed here, which made it possible for a significant amount of oxygen to exist in the water.
"This would have provided enough energy to encourage growth and more complex behavior among primitive, simple forms of animal life such as those found in fossils from this period," he said.
He added that the isolated environment led to the extinction of these life forms because there were not enough new nutrients necessary for the food chain.
The research was published in a scientific journal Precambrian Research.
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