Tubes of hematite, an iron-rich mineral, might be evidence of microbial life that lived around underwater vents billions of years ago. Matthew Dodd/University College London hide caption

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Matthew Dodd/University College London

Shinichi Kuramoto of the Center for Deep Earth Exploration in Japan displays a replica of earthquake fault rock. TOSHIFUMI KITAMURA/AFP/Getty Images hide caption

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TOSHIFUMI KITAMURA/AFP/Getty Images