A new theory of how oceans on Mars came and went over the last 4 billion years suggests they formed several hundred million years earlier and were not as deep as once thought.
Source: Did enormous volcanoes lead to oceans on Mars? – Futurity
An examination of the solar system’s largest volcanic system (Tharsis, on Mars) reveals how oceans could have formed on early Mars. (In other words, Burroughs and his ancient sea beds might have been right.)
A new theory of how oceans on Mars came and went over the last 4 billion years suggests they formed several hundred million years earlier and were not as deep as once thought.
Source: Did enormous volcanoes lead to oceans on Mars? – Futurity