Oxygen levels in the Earth’s atmosphere are likely to have “fluctuated wildly” 1 billion years ago, creating conditions that could have accelerated the development of early animal life, according to new research.
Scientists believe atmospheric oxygen developed in three stages, starting with what is known as the Great Oxidation Event around 2 billion years ago, when oxygen first appeared in the atmosphere. The third stage, around 400 million years ago, saw atmospheric oxygen rise to levels that exist today.
What is uncertain is what happened during the second stage, in a time known as the Neoproterozoic Era, which started about 1 billion years ago and lasted for around 500 million years, during which time early forms of animal life emerged.
“Up until now, scientists had thought that after the Great Oxidation Event, oxygen levels were either low and then shot up just before we see the first animals evolve, or that oxygen levels were high for many millions of years before the animals came along.
“But our study shows oxygen levels were far more dynamic. There was an oscillation between high and low levels of oxygen for a long time before early forms of animal life emerged. We are seeing periods where the ocean environment, where early animals lived, would have had abundant oxygen—and then periods where it does not.
Dr. Benjamin Mills, who leads the Earth Evolution Modeling Group at Leeds and supervised the project, said, “This periodic change in environmental conditions would have produced evolutionary pressures where some life forms may have become extinct and new ones could emerge.”
Dr. Mills said the oxygenated periods expanded what are known as “habitable spaces”—parts of the ocean where oxygen levels would have been high enough to support early animal life forms.
He said, “It has been proposed in ecological theory that when you have a habitable space that is expanding and contracting, this can support rapid changes to the diversity of biological life.
“When oxygen levels decline, there is severe environmental pressure on some organisms which could drive extinctions. And when the oxygen-rich waters expand, the new space allows the survivors to rise to ecological dominance.
“These expanded habitable spaces would have lasted for millions of years, giving plenty of time for ecosystems to develop.”
Full article at Phys.org.
Note that while a decline in oxygen levels could certainly drive some organisms into extinction, the reverse process has no magical powers to produce new organisms. Increased atmospheric oxygen is not a mechanism for generating novel functional biocomplexity. However, an intelligent agent (say, a divine Creator) could use the “habitable space” produced by higher oxygenation to create new species that require more oxygen.