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).
Releases a lot of energy. When hydrogen a highly reactive element reacts with oxygen, it does so using immense force, when the bonds break high amounts of emery is released.
