How oxygen levels fluctuations may have hastened animal evolution

Researchers think that the amount of oxygen in the Earth’s atmosphere changed “wildly” a billion years ago, which could have sped up the development of early mammals.

According to scientists, atmospheric oxygen evolved in three stages, beginning with the Great Oxidation Event approximately two billion years ago, when oxygen first emerged in the atmosphere. Atmospheric oxygen reached its current levels during the third stage, which occurred around 400 million years ago.

Not much is known about what happened during the Neoproterozoic Era, which started about a billion years ago and lasted about 500 million years. It was during this time that the first animal life appeared.

Was there anything unusual about the variations in oxygen levels throughout the Neoproterozoic Era, which may have had a crucial role in the early evolution of animals? Did oxygen levels increase abruptly or gradually?

In sedimentary strata between 541 and 635 million years old, fossilized evidence of early life, known as Ediacaran biota, was discovered. These organisms were multicellular and oxygen-dependent.

A research team from the University of Leeds, with help from the Universities of Lyon, Exeter, and UCL, tried to answer the question by measuring the different kinds of carbon found in limestone rocks from shallow water.

Based on the isotope ratios of the different types of carbon found, the scientists were able to figure out how much photosynthesis there was millions of years ago and how much oxygen was in the air.

As a result of the computations, a record of oxygen levels in the atmosphere for the past 1.5 billion years has been created, which reveals how much oxygen would have diffused into the ocean to support early marine life.

Dr. Alex Krause, a biogeochemical modeller who got his Ph.D. in the School of Earth and Environment at Leeds and was the project’s principal scientist, stated that the findings provide a new viewpoint on the evolution of oxygen levels on Earth.

He added: “For the first two billion years of its existence, the early Earth was anoxic, bereft of oxygen in the air.” The subsequent increase in oxygen levels is known as the “Great Oxidation Event.”

Prior to this discovery, scientists believed that after the Great Oxidation Event, oxygen levels were either low and suddenly shot up right before the evolution of the first animals, or that oxygen levels were high for millions of years before the evolution of the first animals.

However, our research indicates that oxygen levels were considerably more variable. Prior to the emergence of the first forms of animal life, oxygen levels fluctuated between high and low levels for eons. We observe times in which the ocean environment, in which early animals thrived, was rich in oxygen, followed by eras in which it was not. ”

Dr. Benjamin Mills, who runs the Earth Evolution Modelling Group at Leeds and oversaw the experiment, said, “This periodic change in environmental conditions would have caused evolutionary forces that led to the extinction of some life forms and the appearance of others.”

Dr. Mills explained that the oxygenated eras extended what are known as “habitable areas”—regions of the ocean where oxygen levels were high enough to support early animal life.

He said: “In ecological theory, it has been hypothesized that when a livable space is expanding and contracting, this can allow rapid changes in the diversity of living organisms.

“When oxygen levels decrease, there is an intense environmental strain on certain organisms, which may lead to their extinction.”

And as the oxygen-rich waters get bigger, the new space gives the remaining species a chance to rise to the top of the food chain.

These larger areas where people could live would have lasted for millions of years, giving ecosystems plenty of time to change.

The results are written up in a paper called “Extreme fluctuation in atmospheric oxygen levels in the late Precambrian” in the journal Science Advances.