WASHINGTON (CBSDC) – About 420 million years ago, just about all life on Earth was wiped out.

The Ordovician-Silurian extinction event destroyed about 85 percent of all animal and plant life. It’s been blamed on a cooling climate, which caused ice sheets to form and lowered sea levels at a time when most animal life existed in the oceans.

But a new discovery could rewrite the history books about this turbulent era.

Researchers found the fossilized remains of microscopic plankton that showed unusual deformations.

Those deformations looked very similar to what is observed when modern organisms are exposed to high levels heavy metals, such as iron, lead and arsenic.

The scientists suggest metal poisoning could have caused the malformations, and it could help explain what happened on Earth 420 million years ago.

“Metal toxicity, and its fossilized in vivo expressions, could provide the missing link between extinction of faunas on the shelf, and widespread ocean anoxia (lack of oxygen),” say the study authors. “As part of a series of complex systemic interactions accompanying these shifts in ocean conditions, the redox cycling of metals may identify the early phase of the kill mechanisms that culminated in these catastrophic events.”

The study is published in the journal Nature Communications.

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