Are you getting enough minerals? A new theory suggests most of Earth’s mass extinction events could have been caused by a lack of essential trace elements in the world’s oceans, causing fatal deficiencies in marine animals, from plankton to reptiles.

Earth has been hit with five mass extinction events. The two most dramatic ones had pretty clear causes. The dinosaurs were probably wiped out 66 million years ago thanks to a massive meteor falling on modern-day Mexico, while the end-Permian extinction, which wiped out 90 per cent of species 252 million years ago, was probably the result of massive volcanoes in Siberia.

But that leaves three other mass extinctions, with no agreed cause.


“It’s a complex scenario,” says John Long from Flinders University in Adelaide, Australia. He says there are probably a lot of causes conspiring to drive these mass extinctions. But his latest work suggests fluctuations in essential minerals in the ocean could be an important, and so-far completely unexplored, cause.

Essential selenium

Earlier this year, researchers discovered that periods when the ocean had high levels of trace elements – like zinc, copper, manganese and selenium – seemed to overlap with periods of high productivity, including the Cambrian explosion, when most groups of living animals first appeared.

Now they have shown that drops in these elements correlate well with major extinction events. Long and his colleagues did this by focussing on selenium, one of the best-studied trace elements. They found that at the end of the Ordovician, Devonian and Triassic periods – when the three unexplained mass extinctions occurred – selenium levels in the ocean dropped two orders of magnitude lower than their current levels. That puts them well below the amount thought to be critical for all animals.

“The essential trace elements – they’re called essential because without them we die,” says Long. “Life is such a delicate balance between getting the right amount of these things.”

Extinction number six

“We’re not saying this is the whole answer, we’re saying it’s another factor that correlates with these mass extinctions,” says Long.

These fluctuations in trace elements could have had a number of causes. One theory is that, at times when atmospheric oxygen levels were rising, more minerals may have oxidised on land and then washed into rivers and the ocean. So drops in oxygen could have caused the mineral deficiencies.

Or reduced tectonic activity could be to blame. When tectonic plates are moving around, they throw much more mineral-rich sediment into the ocean, says Long. “We don’t know – we don’t have a handle on a lot of these things yet.”

Andrew Glikson at the Australian National University in Canberra says it’s not clear why some of these extinctions would be so abrupt, if gradual drops in trace elements caused them. “However, in order to constrain these possibilities, the precise age of the mass extinctions need to be determined,” he says.

Long says a depletion in selenium usually starts millions of years before a mass extinction actually happens, but the one we’re about to live through is something different. “We’re living in a period where we’ve got selenium at high levels,” he says. “We are on the verge of the sixth mass extinction because of what us bloody humans are doing to the place. It’s got nothing to do with selenium.”

Journal reference: Gondwana Research, DOI: 10.1016/j.gr.2015.10.001

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Image credit: Sheila Terry/SPL