Geological evidence for multiple climate transitions on Early Mars

Landforms and deposits observed on the Martian surface suggest that Mars’ early climate supported rivers and lakes over a time span of more than a billion years. But, like Earth, which has over the past billion years experienced periods of global glaciations and hyperthermals, the climate history of Early Mars may have been intermittent. Here we synthesize sedimentary and erosional evidence for multiple climate transitions on Early Mars. We suggest that Mars did not undergo a single wet-to-dry transition, but rather experienced seven major climate transitions, with the planet intermittently under climates warm enough to support surface liquid water even after 3.0 billion years ago (Ga). However, there is evidence for long dry spells, with some locations fully dry after 3.6 Ga. We evaluate hypotheses for the cause of the climate transitions, such as volcanic eruptions and changes in mean obliquity. Testing the sequence of events and understanding the underlying drivers of environmental change will require future missions to Mars.