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Earth’s first animals may have been sea sponges

Sea sponges were among the first animal groups to evolve on Earth, but the discovery of new chemical evidence now pegs the advent of the species at 120 million years earlier than was previously thought, New Scientist reports. Researchers suspected early animals would need to produce chemicals that allowed them to live in harmony with the bacteria and microbes that dominated the ancient world. So, they went hunting for “chemical fossils,” traces of sterols—steroids with antibacterial properties—to determine when the first sponges started to appear. They found the steroids in rock and oil samples from Oman, Siberia in Russia, and India that date to between 660 million and 635 million years old, they report this week in Nature Ecology & Evolution.

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