Scientists have discovered evidence that a pocket of complex life may have evolved on Earth more than 2 billion years ago – only to disappear and take another 1.5 billion years to evolve back to that level. The controversial finding could rewrite our understanding of life on Earth and beyond.
Life seems to have begun fairly rapidly after the Earth formed about 4.5 billion years ago. Direct evidence suggests that microbes were abundant 3.5 billion years ago, and other fossils date back to 3.7 billion years ago. Other evidence even suggests that the Earth may have been colonized very rapidly as early as 4.3 billion years ago, but these fossils are highly controversial.
Still, most life on Earth consisted of simple, single-celled organisms. Complex life, including the ancestors of animals, is thought to have evolved about 635 million years ago, when conditions became favorable for larger body sizes.
But that story is thrown into chaos by mysterious structures found in the Francevillian Formation in Gabon. Reaching a relatively large size of up to 17 cm (6.7 in), these flat disc-shaped fossils appear to be early multicellular organisms. The only problem? They 2.1 billion yearsor this complex is about 3.5 times older than the currently accepted age of life.
Understandably, other scientists have disagreed with the claim that these fossils represent organisms. Other possible explanations are that the structures are the result of inorganic pyrite, concretions, or other non-biological processes.
To investigate further, the researchers in the new study conducted geochemical analysis of marine sedimentary rocks around the controversial fossils. Interestingly, they discovered evidence of an oxygen and phosphorus pulse in the area just before the time of the Francevillian structures.
It appears that two cratons—very old, solid sections of tectonic plates—crashed into each other in the region, triggering a series of underwater volcanic eruptions that created a shallow inland sea rich in these life-giving nutrients.
“This created a local environment where cyanobacterial photosynthesis was abundant for a long period of time, leading to oxygenation of the local seawater and the formation of a large food source,” said Dr. Ernest Chi Fru, lead author of the study. “This would have provided enough energy to drive 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.”
So if complex life really did begin about 1.5 billion years ago than we think, why isn’t there more evidence of it around the world? The researchers say that these favorable conditions were limited to this inland sea—beyond that, the Earth was still pretty hostile to complex life. And even then, geologically speaking, the oasis was short-lived, and these creatures eventually went extinct.
Therefore, these life forms that were ahead of their time are not the ancestors of animals living today. Instead, they are a surprisingly early evolutionary experiment in more complex forms that also failed. Evolution does not seem to have had a chance to try again until about 635 million years ago, when favorable conditions were more common.
Professor Abderrazzak El Albani from the University of Poitiers, France
The idea is certainly intriguing, but not all scientists agree with all the conclusions reached by this study. Just as there has been debate over whether structures in the Francevillian formation represent fossils, more evidence may be needed to support these unusual claims.
Professor Graham Shields of University College London, who was not involved in the research, said: “I don't disagree with the idea that there were higher nutrients 2.1 billion years ago, but I'm not convinced that this would have led to the diversification to form complex life forms.” BBC news.
The research was published in the journal Precambrian Research.
Source: Cardiff University