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NASA’s Curiosity rover has been exploring Gale Crater on Mars since 2012, and has collected data showing many chemical variations in the crater’s sedimentary rocks. A team led by Joel Hurowitz of Stony Brook University in New York analysed the data and conclude that older rocks seem to have formed in relatively cold climates. By contrast, younger sediments suggest that environmental conditions were warmer and wetter. The crater could have been hospitable to life between 3.8 billion and 3.1 billion years ago, not long after it was first formed.