The Tharsis and Elysium regions of Mars were volcanically active over billions of years, that caldera eruptions were episodic but were especially numerous 100 to 200 million years ago, and that the most recent lava flows on Mars may be as young as two million years. The findings are consistent with previous studies of Mars Global Surveyor data as well as Martian shergottite meteorites that suggest intermittent magmatism from 165 to about 500 million years ago.
The analysis shows volcanic craters resurfaced as little as two million years ago, "suggesting that the volcanoes are potentially still active today." Some areas show activity as recently as 4 million years ago, which amounts to the most recent one per cent of the planet's history. Researchers dated the volcanic features by counting craters on the planet's surface. Since asteroids and other material from space bombard Mars at a known rate, scientists can estimate dates by looking at how the smooth lava becomes pock-marked with craters.
The surface appearance of the moon is largely craters and dark lunar maria. The mares seas were thought to be water from their dark and flat appearance. It was realized that these areas were upwelling lava flooding portions of the moon, leaving these dark areas. Interestingly the lunar far side has very little maria. There is no longer volcanic activity on the moon. This ended long ago when the moon, being a smaller body than the earth, cooled quickly after its formation. Internal heat is generally necessary for volcanic activity.
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