Health When life vanished into thin air

When life vanished into thin air

Take a deep breath: it seems the earth’s oxygen levels can fall dangerously low, leading to mass extinction.

Don’t hold it for too long though – research from the University of Tasmania shows it only happens once every 50-100 million years at most.

Still, that’s a relatively short time span compared to cycles lasting more like a billion years, which is what scientists previously thought.

Geologists believe the proportion of oxygen in the earth’s atmosphere has varied at different times in its history from the current 21 per cent.

Analysis of trace metals in the oceans reveal highs greater than 25 per cent and lows of less than 10 per cent.

But scientists once thought there had been only two major oxygen cycles – more than a billion years apart – but the University of Tasmania’s research identifies eight major peaks followed by dramatic troughs.

Lead researcher Ross Large believes the troughs coincide with mass extinction events.

“The picture is now emerging that nearly all major Earth processes in geological history were cyclical in nature, with several orders of cycles superimposed,” Professor Large says.

“Supercontinent cycles led to mountain building cycles, which stimulated nutrient cycles, oxygen cycles, evolutionary cycles, climate cycles and mass extinction cycles.”

The theory is that change is driven by continents colliding to form mountain chains. These feed the ocean with nutrients as they erode, stimulating evolution and gradually increasing oxygen as life flourishes.

Long periods without mountain formation and resulting nutrient flow restrict the growth of living things and limit the oxygen they produce, eventually leading to a plunge in oxygen levels, causing mass extinction.

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