Visible to the stargazer, the moon’s surface is covered with dead volcanoes, impact craters, and formations from previous lava flows. Early scientists thought the dark stretches of the moon might be oceans and so named such features ‘mare’, from the ancient langage Latin for ‘seas’.

Rather than oceans of water, these stretches and darkened spots of the moon were made up of pools of hardened basaltic lava. Early in the moon’s history, the interior was molten enough to produce volcanoes that quickly cooled and hardened. Also, lava was able to burst through from the crust of the moon when large enough asteroids broke through the surface. The evidence of asteroids can easily be seen through a telescope (picture).

Early in the solar system’s history, all of the planets and moons suffered through a period of heavy bombardment, with large rocks captured by gravity crashing into the moon’s surface.

On Earth, plate tectonics and erosion covered up much of the evidence from this period while the atmosphere helped to burn up some of the smaller asteroids before they hit the Earth’s surface The moon however lacked all three of these cleanup elements, so the history of the solar system is preserved on its surface.

While this period of bombardment ended about 3.8 billion years ago, it wasn’t responsible for all of the craters on the moon. Large and small asteroids contined to pelt the surface, leading to overlapping craters and craters on top of the lava flows.

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