Aussie scientists have presented a groundbreaking research that examines the cause of three mass extinctions, suggesting that major changes may have been affected by a lack of motion in the Earth’s crust. Ancient sedimentary rocks present in the seabed were examined using laser techniques to determine the levels of selenium – a trace element. Cobalt, zinc, manganese, copper, along with selenium, are considered vital for life.

The researchers plotted the changes in levels of selenium over a period of 600 million years and found that mass extinction events coincided with a sharp fall in selenium levels to one to two parts per million (ppm). The three least understood extinction events can now be better examined with these findings.

John Long, palaeontologist at Flinders University, said that the observations pointed to the key role of selenium in the Ordovician, Devonian and Triassic mass extinctions. “To solve a mass extinction event is like solving one of the biggest mysteries of science,” he told SMH. “But we are quite convinced this is a major factor.”

The Cretaceous and Permian extinctions were caused by a meteor strike and gigantic volcanic eruptions, respectively. However, climate change, volcanic eruptions and earthquakes are some of the causes that have been attributed to the other three mass extinctions that primarily affected marine flora and fauna. This is explained by the fall in selenium levels that coincide with the slowdown or ceasing of major plate tectonic activity; nutrients from the Earth’s crust are released by tectonic movement, into rivers that flow out into the ocean.

“When plates collide it is a mountain-building event ... and over millions of years the mountains erode releasing nutrients into the rivers and oceans,” said Long. “But when tectonic activity is stable, there aren't the nutrients flowing into the ocean and so the existing amount in the oceans is eaten up by living organisms and eventually it reaches a depletion point.”

Researchers also pointed out previous studies that have established links between human health and selenium levels. Long said that the regions of Africa and China deficient in selenium were associated with the emergence of major diseases such as Ebola, AIDS, avian flu and SARS.

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