A team of scientists say they have found new evidence to support their theory that complex life on Earth may have started 1.5bn years earlier than previously thought.
The team, working in Gabon, says it has found evidence deep in the rocks that show the environmental conditions for animal life 2.1bn years ago.
But they say the parasites were confined to the inland sea, did not spread around the world and eventually died out.
Opinions are very different from conventional thinking and not all scientists agree.
Most experts believe that animal life began 635m years ago.
The research adds to the ongoing debate about whether the hitherto unexplained structures found in Franceville, Gabon are actually fossils.
Scientists looked at the rock surrounding the formations to see if they contained evidence of nutrients such as oxygen and phosphorus that could have supported life.
Professor Ernest Chi Fru at Cardiff University worked with an international team of scientists.
He told BBC News that, if his theory is correct, these life forms would be similar to slime mold – a brainless single-celled thing that reproduces by spores.
But Professor Graham Shields of University College London, who was not involved in the research, said he had his doubts.
“I’m not against the idea that there was a high nutrient density 2.1bn years ago but I’m not convinced that this would lead to the diversification to create complex life,” he said. suggest that more evidence was needed.
Prof Chi Fru says his work has helped prove ideas about the processes that create life on Earth.
“We say, look, there are fossils here, there is oxygen, which stimulates the appearance of the first complex organisms,” he said.
“We see the same process as in the Cambrian period, 635m years ago – it helps to bring that back. It helps us to finally understand where we all came from,” he added.
The first suggestion that complex life may have started much earlier than previously thought came about 10 years ago with the discovery of something called the Francevillian structure.
Professor Chi Fru and his colleagues said the structure was made up of fossils that pointed to evidence of life that could “sway” and move on its own.
The findings were not accepted by all scientists.
To find more evidence of their theories, Professor Chi Fru and his team have now analyzed sediment cores dug from the rock of Gabon.
The chemistry of the rock has shown evidence that the “laboratory” of life was created before the emerging structure.
They believe that the high levels of oxygen and phosphorus were created by two continental plates colliding under the water, causing volcanic eruptions.
The collision cut off part of the water in the oceans, and created a “nourishment-rich shallow inland ocean.”
Prof Chi Fru said that this protected environment had the conditions to allow photosynthesis, which leads to a large amount of oxygen in the water.
“This would have provided enough energy to promote the increase in body size and more complex behavior observed in ancient life forms, such as those found in fossils,” he said. long ago,” he said.
But he says the isolated environment also led to the extinction of life forms because there were not enough new nutrients to sustain the food supply.
PhD student Elias Rugen of the Natural History Museum, who was not involved in the research, agreed with some of the findings, saying it was clear that “the cycles of carbon, nitrogen, iron and phosphorus were all doing something different. unprecedented in the history of the world.”
“There is nothing to say that complex microbial life could not have emerged and flourished as early as 2bn years ago,” he said, but added that more evidence is needed supporting ideas.
The findings were published in the scientific journal Precambrian Research.
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