Science

Study links spikes in oxygen levels with bursts of evolution

A new study adds support to the theory that spikes in oxygen levels helped make conditions favorable for bursts of early animal evolution
A new study adds support to the theory that spikes in oxygen levels helped make conditions favorable for bursts of early animal evolution
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A new study adds support to the theory that spikes in oxygen levels helped make conditions favorable for bursts of early animal evolution
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A new study adds support to the theory that spikes in oxygen levels helped make conditions favorable for bursts of early animal evolution

Life on Earth may have begun billions of years ago with a quiet, single-celled whimper, but it really arrived with a bang about 540 million years ago. Within a relatively short period of time, life burst forth into an incredible diversity of forms, in an event that has since come to be known as the Cambrian explosion. Now, an international team of scientists has found clues to what may have caused that – spikes in oxygen levels.

The Cambrian explosion has long been studied as probably the most important event in the history of evolution of life on Earth. It's fairly clear in the fossil record too – prior to that time, signs of life are mostly limited to trace fossils of single-celled organisms and some simple multi-celled creatures. But starting around 541 million years ago, life really took off, expanding into all the major groups we see today over just 13 to 25 million years.

But exactly what triggered the Cambrian explosion has remained a mystery. One long-standing theory suggests that surging oxygen levels led to these bursts of evolution in animals, and the current study has found new evidence to support this idea.

To do so, the researchers first collected marine carbonate samples from along the Aldan and Lena rivers in Siberia – areas that would have been shallow seas during the Cambrian period, bustling with life. The team then analyzed the carbon and sulfur isotopes in these samples, which allows for the calculation of the levels of oxygen floating around in the shallow ocean and atmosphere during those times.

Sure enough, high levels of oxygen were found around the times of the diversity explosion, with a particularly strong amount present between 524 and 514 million years ago. Interestingly the reverse also seemed to prove true – low levels of oxygen accompanied a later extinction event, occurring between 514 and 512 million years ago.

"This is the first study to show clearly that our earliest animal ancestors experienced a series of evolutionary radiations and bottlenecks caused by extreme changes in atmospheric oxygen levels," says Graham Shields, corresponding author of the study.

Extra oxygen is definitely vital for larger lifeforms, but it might have just been one part of the story. It's thought that the end of the Snowball Earth period about 100 million years earlier may have washed more nutrients into the seas, leading to increased diversity of single-celled organisms. Together, these favorable conditions might have let life finally run wild with creativity.

The study was published in the journal Nature Geoscience.

Source: Oxford University

4 comments
Nik
All life on Earth is carbon based, and access to carbon is primarily via CO2, and following the emergence from the Snowball Earth event, there was also a very high level of CO2 in the atmosphere, estimated at 7000 ppm, which makes today's puny 400 ppm look miserable. So, its probable that it was the combination of high oxygen coupled with the high CO2 level that was responsible for the Cambrian explosion. Combined with the fact that there was little competition for the various niches in the environment, as virtually all life had died out while Earth was a snowball, Today's low level of CO2 could also be partly responsible for the current extinction event. The same conditions were present during the Permian extinction.
Vernon Miles Kerr
Looking at life-formation and evolution from this perspective makes one appreciate the trial-and-error, cement-mixer, process that led to Earth-as-we-know-it today. What are the chances that we humans would not have even made it through? Pretty great. What are the chances that this type of process has happened in a near-by star system and has resulted in another intelligent, curious, creative animal like we are? Pretty remote. That remoteness hints that if there are intelligences interacting with humans, today, they must have the technology to come pretty damn far, pretty damn fast — if not INSTANTANEOUSLY. But quantum-entanglement being what it is... such tech is not beyond imagining.
amazed W1
When did plants that photosynthesise first appear? Boom goes the oxygen once they get established, whether lots of lovely CO2 or global warming started them off!
ljaques
The Grays had very efficient terraforming engines way back then, didn't they? Our planet was groomed, folks. <wink>