Ocean Changes Dramatically Reduced the Oxygen Levels Needed for Life on Earth

Chemical changes in the oceans from approximately 800 million years ago influenced Earth considerably. It almost ruined the oxygen-abundant atmosphere that developed life as we know it today, according to a new study.

Back then, like nowadays, the planet possessed something dubbed an “oxidizing” atmosphere, conducted by phytoplankton – the “plants” in the ocean – discharging oxygen during photosynthesis.

The new study led by a team of researchers from the University of Exeter, Leeds, Toulouse, Nanjing, and London, indicated ocean changes at the beginning of the Neoproterozoic era (approximately 800 million years ago) might have blocked the phosphorus – an essential element for life – locking away the phytoplankton development and oxygen release.

The recent study states that the amount of phosphorus available then it was enough only for supporting the oxidizing atmosphere. It also prevented a return to the lowering (oxygen-less) atmosphere that was over a billion years ago.

About 800 million years ago, ocean changes reduced the oxygen levels needed for life

“We know ocean chemistry affects the cycle of phosphorus, but the impact on phosphorus availability at this time hadn’t been investigated until now,” explained Dr. Romain Guilbaud from Toulouse (CNRS).

The team analyzed ocean sediments and discovered that iron mineral was essential in eliminating the phosphorus from the ocean. The phytoplankton increase, on the other hand, it’s known for its ability to boost up the atmospheric oxygen. It does such a thing because it divides the oxygen and carbon and discharges the oxygen, so the plants die, and their carbon is concealed. So, it won’t recombine with oxygen to develop carbon dioxide.

Despite decreases in photosynthesis and that organic concealing of carbon, both due to scarce phosphorus, the oxygen dropped no lower than 1 % of actual levels. It was “just enough” to keep an oxidizing atmosphere, according to the study.

“[…], if phosphorus levels in the water had dropped any lower, it could have tipped the world back into a “reducing” atmosphere suitable for bacteria but not for complex life,” stated Prof. Tim Lenton from the University of Exeter.

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