Oxygenation and Animals: Explaining Air in the Ocean

First Posted: Mar 09, 2014 06:45 PM EDT

A recent study shows that the first animals may have oxygenated the ocean, contrary to traditional believes about its rise in oxygen triggered development.

According to researchers from the University of Exeter, the study investigated how animals evolved to require small amounts of oxygen to live.

"There had been enough oxygen in ocean surface waters for over 1.5 billion years before the first animals evolved, but the dark depths of the ocean remained devoid of oxygen," said professor Tim Lenton of the University of Exeter, who led the new study, via a press release. "We argue that the evolution of the first animals could have played a key role in the widespread oxygenation of the deep oceans. This in turn may have facilitated the evolution of more complex, mobile animals."

Researchers examined the depth of the ocean which could have been oxygenated during Neoproterzoic Era (from 1,000 to 542 million years ago) without requiring an increase in atmospheric oxygen.

Background information from the study notes that determining oxygen levels is crucial to both the balance of oxygen supply and demand. When oxygen is created by the sinking of dead organic material into the depths of the ocean, researchers argue that the first animals reduce the supply of organic matter.

The sponges feed off of water that's pumped through their bodies and then filtered out through tiny particles of organic material that helps oxygenate the shelf seas they live in. They also work to naturally select larger phytoplankton that help sink faster through the lessening of oxygen's demand in the water.

Thus, animals can increase the removal of essential nutrient phosphorus in the ocean, which also works to oxygenate the shelf sea levels.

"The effects we predict suggest that the first animals, far from being a passive response to rising atmospheric oxygen, were the active agents that oxygenated the ocean around 600 million years ago," Lenton said, via the release. "They created a world in which more complex animals could evolve, including our very distant ancestors."

Professor Simon Poulton of the University of Leeds, who is a co-author of the study, added: ″This study provides a plausible mechanism for ocean oxygenation without the requirement for a rise in atmospheric oxygen. It therefore questions whether the long-standing belief that there was a major rise in atmospheric oxygen at this time is correct. We simply don't know the answer to this at present, which is ultimately key to understanding how our planet evolved to its current habitable state. Geochemists need to come up with new ways to decipher oxygen levels on the early Earth.″

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More information regarding the study can be found via the journal Nature Geoscience. 

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