The oldest fossils yet known—an estimated 3.7 billion years old—were announced Wednesday, pushing back evidence of life on Earth by about 220 million years. These remains of ancient microbes were found in Greenland after they were exposed by melting ice—something that may become more common as the planet warms.

The fossils are known as stromatolites and are the evidence of ancient water-based bacterial colonies, which cemented sediments together into distinctive layers with carbonate. Before this new discovery, the oldest known fossils were 3.48-billion-year-old stromatolites found in Western Australia.

(National Geographic)