One of the biggest riddles in Earth’s history is why animals did not evolve after a spike in oxygen levels approximately 2.3 billion years ago. Instead, despite what scientists had thought was a period of relatively high oxygen, the evolution of life on Earth stalled for what is dubbed the ‘boring billion’.
Earth’s early atmosphere has seen two major spikes in oxygen concentration — one roughly 2.3 billion years ago, dubbed the ‘great oxygenation event’, and a second 800 million years ago. The evolution of complex life only took off after this second peak. Now researchers say that fluctuations in oxygen levels probably kept evolution in check during the intervening period.
Walter stresses, however, that genetic innovations are also crucial for the evolution and diversification of complex life. The evolutionary engine did not truly rev up for another 260 million years after the second oxygenation event, when the Cambrian Explosion gave rise to modern animal phyla in just 20 million years — a geological blink of the eye.
Hmmm. Maybe they were only pretending to be boring.
See also: The Science Fictions series at your fingertips (origin of life)
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