Episode 294 Markings discovered on rocks from Mars look to be good evidence that microbial life once existed on the Red Planet. NASA’s Perseverance rover spotted little speckles on rocks in part of Jezero crater, and minerals usually formed in the presence of water. New analysis suggests these markings also contain signs of organic compounds. Presented with the possibility of microbial Martians, can we now say Mars really did once have life? Dark energy, the mysterious force thought to be driving the expansion of the universe, might be getting weaker. If it is, that completely upends our understanding of the universe - from one that’s getting bigger and bigger, to one that could eventually collapse in a “big crunch”.  Results from the Dark Energy Spectroscopic Instrument (DESI) in Arizona may be the biggest discovery about dark energy we’ve had in 25 years. Last year we had the controversial discovery that “dark” oxygen may be produced by metallic nodules on the seafloor. But it was widely contested and the exact mechanism unknown. But researchers in China now think they’ve figured out what’s going on - dark oxygen could be key to keeping deep sea creatures alive, with implications for life beyond Earth. Chapters: (00:31) Suggestions of past life on Mars (7:42) Dark energy and how the universe might end (11:56) Solving the mystery of dark oxygen Hosted by Rowan Hooper and Penny Sarchet, with guests Jacob Aron and Michael Le Page. To read more about these stories, visit https://www.newscientist.com/ Video credit: Perseverance Explores the Jezero Crater Delta Learn more about your ad choices. Visit megaphone.fm/adchoices