The evidence that indicates there was once tectonic activity on mercury, venus, and mars

Mercury has no maria like the Moon, but billions of years ago lava flows formed intercrater plains. Mercury also has cliffs, called scarps, that are hundreds of kilometers long. Scarps have formed when Mercury's crust shrank and buckled as its interior cooled. 

Venus has more than a thousand large volcanoes and hundreds of thousands of smaller volcanic features. Most of the surface is covered with solidified lava flows. The larger volcanoes are often shielded volcanoes, similar to Earth's, which form from lava flowing up through the volcano's center. 

The tectonic features on Mars are the largest in the solar system: Olympus Mons and the Tharsis Ridge volcanoes dwarf Earth's volcanoes are the largest known in the Solar System. Olympus Mons is four times as high as the Mount Everest. Valles Marineris is a canyon on Mars that is deeper than the Grand Canyon and long enough to reach across the whole of the US. 

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