Early climate on Mars

Based on mineral and environmental data gathered by the Mars Science Laboratory Rover Curiosity, a study estimates that Martian carbon dioxide levels approximately 3.5 billion years ago were orders of magnitude lower than the level of carbon dioxide needed to warm early Mars as indicated by climate models, suggesting that mechanisms as yet unknown reconciled the presence of a lake environment with an atmosphere incapable of warming the site to temperatures above freezing. - Read at PNAS.org

Article #16-16649: “Low Hesperian PCO2 constrained from in situ mineralogical analysis at Gale Crater, Mars,” by Thomas F. Bristow et al.