Approximately how long ago is the period of abundant surface liquid water estimated to have occurred?

Answer

Roughly three to four billion years ago.

Geological evidence strongly suggests that the period when liquid water flowed across the Martian surface in rivers and lakes occurred roughly three to four billion years ago, before the planet lost most of its atmosphere.

Approximately how long ago is the period of abundant surface liquid water estimated to have occurred?

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Astronomers Found Oceans of Water on Mars - YouTube

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