http://www.marsdaily.com/reports/Curiosity_rover_sharpens_paradox_of_ancient_Mars_999.html Curiosity rover sharpens paradox of ancient Marsby Staff WritersPasadena CA (JPL) Feb 07, 2017 Please Register or Log in to view the hidden image!Bedrock at this site added to a puzzle about ancient Mars by indicating that a lake was present, but that little carbon dioxide was in the air to help keep a lake unfrozen. Image courtesy NASA/JPL-Caltech/MSSS. For a larger version of this image please go here. Mars scientists are wrestling with a problem. Ample evidence says ancient Mars was sometimes wet, with water flowing and pooling on the planet's surface. Yet, the ancient sun was about one-third less warm and climate modelers struggle to produce scenarios that get the surface of Mars warm enough for keeping water unfrozen. A leading theory is to have a thicker carbon-dioxide atmosphere forming a greenhouse-gas blanket, helping to warm the surface of ancient Mars. However, according to a new analysis of data from NASA's Mars rover Curiosity, Mars had far too little carbon dioxide about 3.5 billion years ago to provide enough greenhouse-effect warming to thaw water ice. The same Martian bedrock in which Curiosity found sediments from an ancient lake where microbes could have thrived is the source of the evidence adding to the quandary about how such a lake could have existed. Curiosity detected no carbonate minerals in the samples of the bedrock it analyzed. The new analysis concludes that the dearth of carbonates in that bedrock means Mars' atmosphere when the lake existed - about 3.5 billion years ago - could not have held much carbon dioxide. The article concludes..... "When two lines of scientific evidence appear irreconcilable, the scene may be set for an advance in understanding why they are not". http://www.marsdaily.com/reports/Curiosity_rover_sharpens_paradox_of_ancient_Mars_999.html Interesting..... Perhaps volcanic/eternal heating source?