PITTSBURGH (KDKA) – Sea sponges were most likely the first animals on earth according to a new study.

MIT researchers say they have discovered molecular fossils of sea sponges in 640-million year old rocks.

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MIT says the rocks significantly predate the Cambrian explosion, or the period in which most animal groups took over the plant, which was about 540 million years ago.

According to an MIT news release researchers say:

“We brought together paleontological and genetic evidence to make a pretty strong case that this really is a molecular fossil of sponges,” says David Gold, a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “This is some of the oldest evidence for animal life.”

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The results were published this week in the Proceedings of the National Academy of Sciences.

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MIT posted this video about the study.

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You can read more about the discovery here.