Approximately how long ago is early Mars theorized to have possessed conditions capable of sustaining liquid water on its surface?

Answer

3 to 4 billion years ago

The Mars Ocean Hypothesis posits that early Mars, approximately 3 to 4 billion years ago, was warm enough and had a thick enough atmosphere to sustain liquid water.

Approximately how long ago is early Mars theorized to have possessed conditions capable of sustaining liquid water on its surface?
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