An image of a rock with fossilized stromatolites, tiny layered structures from 3.7 billion years ago that are remnants from a community of microbes. Found in a newly melted part of Greenland, Australian scientists reported in the journal Nature that the stromatolites lived on an ancient seafloor at a time when Earth’s skies were orange and its oceans green. They describe the stromatolites as perhaps the oldest fossil found so far on Earth. (Allen Nutman/University of Wollongong)