Oxygen jump link to species spread

Rapidly rising oxygen levels more than 400 million years ago seems to have been a key driver in promoting a rapid expansion of biodiversity, new research has found.

Scientists led by David Fike, of the Earth and Planetary Sciences department at Washington University in St Louis, US, used geological data from areas in the west, north and east United States, as well from Canada, South America and Estonia to estimate levels of dissolved inorganic carbon through deep history.

The calculations served as proxy measurements for oxygen density. The team found that levels jumped enormously from about 14% 460 million years ago to 24% just 10 million years later.

The increase coincides with an explosive evolutionary radiation of new species (especially marine species) called the Great Ordovician Biodiversification Event.

A 2010 analysis of the biodiversity bloom, led by French geophysicist Thomas Servais of the University of Lille, concluded that it was “probably the result of a combination of several geological and biological processes and the positive feedbacks resulting from them.”

In the new paper Fike and his colleagues agree. Around the time of the event, they note, the Earth reached “near modern” levels of oxygen for the first time.

“It should be stressed that this was probably not the only reason why diversification occurred at that time,” says Fike. 

“It is likely that other changes – such as ocean cooling, increased nutrient supply to the oceans and predation pressures – worked together to allow animal life to diversify for millions of years.”

The research could not determine the precise causal relationship between increased oxygen and diversity. The scientists note that it cannot be determined if the effect of the higher oxygen levels was direct, or if it was passive, simply expanding the range of environments life could inhabit.

“Oxygen and animal life have always been linked, but most of the focus has been on how animals came to be,” says co-author Matthew Saltzman, of Ohio State University. 

“Our work suggests that oxygen may have been just as important in understanding how animals came to be so diverse and abundant.”

The research is published in the journal Nature Geoscience.

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