Complex life may have been wiped out on Earth before emerging again 1.5 billion years later, according to groundbreaking new findings.
The claims challenge an established concensus that living organisms first developed much more recently.
"We are proposing that macrobiological complexity [in] evolution happened at least twice in Earth's history, first at 2.1 billion years ago and then after 635 million years ago," lead researcher Renest Chi Fru from Cardiff University told CGTN Europe.
An artists impression of the slime of living organisms which may have existed more than a billion years ago. /Abderrazak El Albani
While studying fossils from the African country of Gabon, the team detected a high concentration of phosphorus, an essential component of life.
"This nutrient brought some kind of energy to make life, that is able to join forces to go from cellular to multicellular life," one of the team, Abderrazak El Albani from Université de Poitiers, told CGTN Europe.
Second life
He explained there were two big glaciation events in the Earth's history, one around 2.5 billion years ago and the other some 750 million years ago that created an ideal environment for life each time.
Another crucial element, oxygen, was also found deep within the rocks, which the group believes could be a result of underwater volcanic activity after two continental plates collided.
This environmental evidence points to a two-step process of the formation of complex life.
One of the fossils studied by the team /Abderrazak El Albani
Criticism and doubts
Conventional science regards the event at around 650 million years ago as the origin of complex life, however the discovery of a possible ecosystem in the Franceville Basin near Gabon challenges that.
Fru explained that while their study showed evidence of an environment for complex life, it had apparently failed to spread globally and eventually died out "because of hostile seawater conditions… and the setting in which this occurred was isolated in an inland sea cut off from the global ocean."
The later emergence of life 650 million years ago was more widespread because it "occurred when global marine conditions were more accommodating, leading to global spread to the ecological dominance we see today in animals and plants," he added.
The team faced a backlash for their findings because of conflicts with existing research, but El Albani said researchers were sometimes too dogmatic when examining new ideas.
"You should be open-minded. Otherwise you cannot be a scientist or researcher," he said.
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