March 5, 2024

“Wildly Fluctuating” Oxygen Levels May Have Accelerated Animal Evolution

Fossil records of early animals from Mistaken Point Ecological Reserve in Canada. Fossil records of early animals from Mistaken Point Ecological Reserve in Canada.” But our study shows oxygen levels were far more vibrant. There was an oscillation in between low and high levels of oxygen for a long time before early forms of animal life emerged. We are seeing durations where the ocean environment, where early animals lived, would have had abundant oxygen– and then periods where it does not.

Fossil records of early animals from Mistaken Point Ecological Reserve in Canada. Credit: Dr. Emily. G. Mitchell– University of Cambridge
Oxygen levels in the Earths environment are likely to have “changed wildly” one billion years back, developing conditions that could have accelerated the advancement of early animal life, according to brand-new research study.
Researchers think climatic oxygen established in 3 phases, beginning with what is referred to as the Great Oxidation Event around two billion years ago, when oxygen first appeared in the environment. The 3rd stage, around 400 million years ago, saw atmospheric oxygen rise to levels that exist today.
What is unpredictable is what happened during the 2nd phase, in a time called the Neoproterozoic Era, which started about one billion years ago and lasted for around 500 million years, during which time early forms of animal life emerged.

The question scientists have tried to respond to is– was there anything amazing about the modifications to oxygen levels in the Neoproterozoic Era that might have played an essential function in the early advancement of animals– did oxygen levels suddenly increase or was there a gradual increase?
Fossilized traces of early animals– called Ediacaran biota, multi-celled organisms that needed oxygen– have been found in sedimentary rocks that are 541 to 635 million years of ages.
Fossil records of early animals from Mistaken Point Ecological Reserve in Canada. Credit: Dr. Emily. G. Mitchell– University of Cambridge
To answer the concern and try, a research team at the University of Leeds supported by the Universities of Lyon, Exeter, and UCL, utilized measurements of the various types of carbon, or carbon isotopes, found in limestone rocks taken from shallow seas. Based on the isotope ratios of the various types of carbon found, the scientists had the ability to determine photosynthesis levels that existed countless years ago and presume atmospheric oxygen levels.
As an outcome of the computations, they have been able to produce a record of oxygen levels in the environment over the last 1.5 billion years, which informs us just how much oxygen would have been diffusing into the ocean to support early marine life.
Dr. Alex Krause, a biogeochemical modeler who finished his PhD in the School of Earth and Environment at Leeds and was the lead scientist on the project, stated the findings provide a new viewpoint on the way oxygen levels were altering on Earth.
He included: “The early Earth, for the very first two billion years of its presence, was anoxic, lacking atmospheric oxygen. Oxygen levels began to increase, which is understood as the Great Oxidation Event.
” Up until now, scientists had actually thought that after the Great Oxidation Event, oxygen levels were either low and then shot up prior to we see the first animals progress, or that oxygen levels were high for many countless years before the animals occurred.
” But our research study reveals oxygen levels were much more dynamic. There was an oscillation in between low and high levels of oxygen for a long period of time before early types of animal life emerged. We are seeing durations where the ocean environment, where early animals lived, would have had plentiful oxygen– and then periods where it does not.
Dr. Benjamin Mills, who leads the Earth Evolution Modelling Group at Leeds and supervised the project, said: “This periodic change in ecological conditions would have produced evolutionary pressures where some life types may have become extinct and new ones might emerge.”
Dr. Mills said the oxygenated periods expanded what are called “habitable areas”– parts of the ocean where oxygen levels would have been high enough to support early animal life forms.
He stated: “It has actually been proposed in eco-friendly theory that when you have a habitable area that is expanding and contracting, this can support rapid changes to the diversity of biological life.
” When oxygen levels decrease, there is extreme ecological pressure on some organisms which might drive extinctions. And when the oxygen-rich waters broaden, the brand-new space enables the survivors to rise to ecological dominance.
” These expanded habitable spaces would have lasted for countless years, offering a lot of time for environments to establish.”
Reference: “Extreme irregularity in climatic oxygen levels in the late Precambrian” by Alexander J. Krause, Benjamin J. W. Mills, Andrew S. Merdith, Timothy M. Lenton and Simon W. Poulton, 14 October 2022, Science.DOI: 10.1126/ sciadv.abm8191.
Financing: Natural Environment Research Council, Royal Society, Richard Lounsbery Foundation, Leverhulme Research Fellowship, Deep Energy Community of the Deep Carbon Observatory, MSCA-IF.