Between 490 million and 520 million years ago, a swift extinction event wiped out many of the Cambrian lifeforms. Geologists Benjamin Gill and Graham Shields-Zhou thinks they have found the trigger right in the midst of that era. According to their study in this week’s Nature, the ocean’s oxygen level plunged and the sulfur levels rose sharply 499 million years ago, killing off species that could not quickly adapt. That included some, but not all, of the trilobites that ruled the seas of the time.
Gill’s team decided to look at a specific subset of Cambrian extinctions that began 499 million years ago and lasted for 2 million to 4 million years. Other researchers had proposed that low oxygen levels — a condition known as anoxia — could be involved. But no one had marshaled enough evidence to prove that. [
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