The theory says that complex life on Earth may be much older than previously thought.

A group of scientists say they have found new evidence to support their theory that complex life on Earth may have begun 1.5 billion years earlier than previously thought.

The team working in Gabon says they have discovered evidence deep in the rocks that shows environmental conditions suitable for animal life 2.1 billion years ago.

But they say that these organisms were confined to an inland sea, did not spread globally, and eventually became extinct.

These ideas represent a significant departure from conventional thinking, and not all scholars agree with them.

Most experts believe that animal life began about 635 million years ago.

This study adds to an ongoing debate about whether the hitherto unexplained formations found in Franceville, Gabon, are actually fossils.

Scientists examined the rocks surrounding the formations to see if they showed evidence of nutrients such as oxygen and phosphorus that might support life.

Professor Ernest Che Frue at Cardiff University worked with an international team of scientists.

He told BBC News that if his theory was correct, these life forms would be similar to slime mold – a single-celled, brainless organism that reproduces by spores.

But Professor Graham Shields of University College London, who was not involved in the research, says he had some reservations.

“I’m not against the idea of ​​higher nutrients 2.1 billion years ago, but I’m not convinced that this would have led to the diversity needed for complex life,” he said, noting that more evidence was needed.

Professor Chi Fru said his work helped to prove ideas about the processes that lead to the creation of life on Earth.

“We say, ‘Look, there are fossils here, there is oxygen, it stimulated the emergence of the first complex organisms,'” he said.

“We see the same process as happened in the Cambrian, 635 million years ago – and this helps support that. It helps us ultimately understand where we all came from,” he added.

The first hint that complex life may have begun earlier than previously thought came about 10 years ago, with the discovery of the so-called Franceville Formation.

The formation consists of fossils that provide evidence of life that can “move” and move on its own, Professor Chi Fru and colleagues said.

Not all scientists accepted the results.

To find more evidence for their theories, Professor Che Fro and his team have now analyzed sediment samples drilled from rocks in Gabon.

The chemistry of the rock showed evidence that a “laboratory” for life was created just before the formation occurred.

They believe the high levels of oxygen and phosphorus were the result of two continental plates colliding underwater, causing volcanic activity.

The collision cut off part of the water from the oceans, creating a “shallow, nutrient-rich inland sea.”

This protected environment has the conditions to allow photosynthesis, which results in large amounts of oxygen in the water, says Professor Chi Fru.

“This would provide enough energy to fuel the increase in body size and more complex behavior observed in primitive, simple animal-like life forms such as those in fossils from this period,” he said.

But he says the isolated environment also led to the extinction of life forms because there were not enough new nutrients available to support the food supply.

PhD student Elias Rogin at the Natural History Museum, who was not involved in the research, agreed with some of the findings, saying it was clear that “the carbon, nitrogen, iron and phosphorus cycles in the oceans were all doing something fairly unprecedented at this point in Earth’s history.”

“There is no evidence that complex biological life could not have arisen and flourished some two billion years ago,” he said, but added that more evidence was needed to support these theories.