Life tried to establish itself on Earth 1.5 billion years earlier than expected
A new analysis of marine sedimentary rocks reveals evidence of ancient complex life, suggesting that the history of evolution on Earth may be much older than previously thought.
There is still a scientific debate about when exactly complex life forms first appeared on Earth, and the most recent research suggests that previous estimates should be reconsidered, by about 1.5 billion years.
The new theory is based on an analysis of marine sedimentary rocks in the Franceville Basin, near the west coast of Africa, deposited around 2.1 billion years ago. The general consensus has been that animals first appeared around 635 million years ago. Now, an international group of scientists has discovered that rock samples indicate an increase in phosphorus and oxygen in seawater, which has previously been linked to rapid advancements in evolution.
"We already know that an increase in marine phosphorus and oxygen concentrations in seawater is associated with a biological evolution event that occurred about 635 million years ago,"
says Earth scientist Ernest Chi Fru from Cardiff University in the UK.
"Our study adds another, much earlier event to the record: 2.1 billion years ago."
An unusually large number of fossils large enough to be seen without a microscope have been discovered in the Franceville Basin, and it's unclear what to make of them. Previous studies have also suggested that these macrofossils indicate the earliest complex life on the planet.
In the study, the researchers link the nutrient enrichment of the water to the collision of two ancient continents, which then created a shallow inland sea and the conditions for cyanobacteria photosynthesis—a chemical process that would have led to a more favorable underwater environment for biological complexity. This would have created a natural laboratory for organism diversity and evolutionary leaps in size and structure, the researchers argue. However, because the water basin was isolated, these more sophisticated life forms may not have spread elsewhere or survived the subsequent evolutionary leap.
“We believe that the submarine volcanoes, which emerged following the collision and suturing of the Congo and São Francisco cratons into a single main body, further restricted and even isolated this section of water from the global ocean, creating a shallow, nutrient-rich inland sea,”
says Chi Fru.
The findings may indicate that complex life on Earth evolved in two stages: an initial stage following the first significant increase in atmospheric oxygen, which occurred 2.1 billion years ago, and a second stage following a subsequent increase, which happened 1.5 billion years later. Complex life may have emerged multiple times over the millennia, as suggested by other studies. Scientists are still working to determine what types of life evolved and when, and there is no guarantee that all evolutionary leaps were maintained. Naturally, delving so far back in time is challenging: it requires careful analysis of ancient fossils and environments that might have hosted conditions suitable for what these researchers describe as "macrobiological experimentation."
source: https://www.sciencedirect.com/science/article/pii/S0301926824001669
