07:16 GMT +321 July 2019
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    This rendering provided by Yale University shows a Pentecopterus decorahensis.

    Scientists Say Earth’s First Mass Extinction Was Caused by Critters

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    The world's first known mass extinction, which occurred about 540 million years ago, was not caused by a giant meteorite or volcanic super-eruption, but by the Earth's first animals, a new study suggests.

    For more than three billion years, microbes were the only life on Earth. Then some of these microbes discovered how to photosynthesize, or turn sunlight into energy. The photosynthesis created oxygen, which was toxic to most microbes accustomed to an oxygen-free environment.

    But the microorganisms that were photosynthesizing eventually evolved into complex, multicellular forms called Ediacarans, which took over the planet around 600 million years ago. Ediacarans were largely immobile marine life shaped like discs, tubes, fronds, or quilts.

    Paleontologists call the ensuing period the "Garden of Ediacara," as a reference to the peace and tranquility of the period. That peace prevailed for about 60 million years, until Ediacarans evolved even further into the first animals – that is, organisms that can move independently and eat other organisms.

    These animals ultimately wiped out the Ediacarans, marking the first mass extinction, scientists say.

    "People have been slow to recognize that biological organisms can also drive mass extinction," Simon Darroch, assistant professor of earth and environmental sciences at Vanderbilt University, told Phys.org.

    "But our comparative study of several communities of Ediacarans, the world's first multicellular organisms, strongly supports the hypothesis that it was the appearance of complex animals capable of altering their environments, which we define as 'ecosystem engineers,' that resulted in the Ediacaran's disappearance."

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