The moon is the easiest body in the solar system to observe with the naked eye. People have wondered about the dark and light spots on the surface throughout history. What caused these strange features? People have also questioned what makes up our nearest neighbor.
Children’s fairytales tell us that the moon is made of cheese, but like all bodies in the solar system, rock is the more realistic ingredient. The moon’s surface is covered with dead volcanoes, impact craters, and lava flows, some visible to the unaided stargazer
Early scientists thought the dark stretches of the moon might be oceans, and so named such features mare, which is Latin for “seas” (maria when there are more than one). They are oceans of a sort, but rather than water, such bodies are made up of pools of hardened lava. Early in the moon’s history, the interior was molten enough to produce volcanoes, though it quickly cooled and hardened. Lava also burst from the crust when large enough asteroids broke through the surface.
The moon’s surface shows plenty of evidence of asteroids. Early in the solar system’s history, all of the planets and moons suffered through a period of heavy bombardment, as the last of the large rocks were captured by their gravity and crashed into their 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 offenders before they hit the surface. But the moon lacks all three of these cleanup elements, so the history of the solar system is preserved on its surface.