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 thought.
A team working in Gabon says they have found evidence deep in the rocks showing the environmental conditions in which animals lived 2.1 billion years ago.
But they said the organisms were restricted to inland seas and did not spread globally and eventually become extinct.
These ideas run counter to conventional thinking, and not all scientists agree.
Most experts believe animal life began about 635 million years ago.
The study adds further fuel to the debate over whether unexplained formations discovered so far in Franceville, Gabon, are actually fossils.
Scientists looked at the rocks surrounding the formation to see if they showed evidence of containing nutrients such as oxygen and phosphorus that could support life.
Professor Ernest Chi Frew of 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 molds – brainless single-celled organisms that reproduce with spores.
But Graham Shields, a professor at University College London who was not involved in the study, said he had reservations.
“I don’t disagree with the idea that higher nutrients existed 2.1 billion years ago, but I don’t believe that this would have led to diversification into complex life,” he said, suggesting more evidence is needed.
Professor Frew said his work could help prove ideas about the process of the creation of life on Earth.
“We say, look, here are fossils, there’s oxygen, and it stimulated the emergence of the first complex organisms,” he said.
“We’re seeing the same processes that were happening in the Cambrian period 635 million years ago – that helps support that. It helps us ultimately understand where we all came from,” he added.
The first hints that complex life might have begun earlier than previously thought came about a decade ago with the discovery of the Franceville Formation.
Professor Chi Frew and his colleagues said the formation was made up of fossils, which showed evidence of life that could “wiggle” and move on its own.
The findings were not accepted by all scientists.
To find more evidence for their theory, Professor Chi Fru and his team have now analyzed sediment cores drilled from Gabon rocks.
The chemical composition of the rocks suggests that the “laboratory” for life was created before the formations emerged.
They believe that high concentrations of oxygen and phosphorus were created by the underwater collision of two continental plates, creating volcanic activity.
The collision severed a portion of the ocean’s water, creating a “nutrient-rich shallow inland sea.”
Professor Chiveru said this protected environment provides the conditions for photosynthesis, which produces large amounts of oxygen in the water.
“This would have provided sufficient energy to facilitate the increases in body size and more complex behaviors observed in primitive, simple animal-like life forms, such as those found in fossils from this period,” he said.
But he said the isolated environment also led to the demise of life forms because there weren’t enough new nutrients to maintain the food supply.
Elias Rugen, a doctoral student at the Museum of Natural History who was not involved in the study, agreed with some of the findings, saying it is clear that “the ocean carbon, nitrogen, iron and phosphorus cycles are all at this point.” Do something unprecedented” in the history of Earth. “
“There is no doubt that complex biological life could not have emerged and flourished two billion years ago,” he said, but added that more evidence is needed to support these theories.
The research results were published in Scientific journal Precambrian Research.
