Proof that ancient oceans were anoxic, iron-rich could rewrite early Earth history

A new study has revealed that the ancient deep ocean was not only devoid of oxygen but also rich in iron, a key biological nutrient, for nearly a billion years longer than previously thought — right through a key evolutionary interval that culminated in the first rise of animals.

“The implications of our work are far reaching,” said Timothy Lyons, a professor of biogeochemistry and the principal investigator of the study, led by researchers at the University of California, Riverside.

“We will need to rethink, in a fundamental way, all of our models for how life-essential nutrients were distributed in the ocean through time and space,” he stated.

Most scientists agree that the early Earth, before 2.4 billion years ago, contained only trace quantities of oxygen and that the oceans were dominantly full of dissolved iron.

But there is far less agreement among scientists about the chemical composition of the ocean during the middle chapters of Earth’s history in the wake of atmospheric oxygenation—about 2.4 to 0.5 billion years ago—when the diversity of organisms that we know today, including the animals, first got their footing.

The researchers’ new data, the first of their kind, point towards continuous oxygen-poor, iron-rich conditions for 90 percent of Earth”s history, with oxygen and hydrogen sulfide, when present, limited mostly to the surface layers and along the margins of the oceans, respectively.

“Our new knowledge that the deep ocean was anoxic and iron-rich does not mean life had it easy, though,” Lyons stated.

“Enough sulfide could have persisted around the edges of the ocean to severely limit other key nutrients. We are still testing this hypothesis,” he added.

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The study results appeared in the Sept. 8 issue of Nature.

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