Volcanoes are openings in the Earth’s crust that throw out lava, ash, and rocks. Volcanoes form when pressure from the molten magma builds up and finally erupts into a volcano! When that lava cools, it turns into a solid that makes new land. Millions of years ago, when Earth was covered in volcanoes, those volcanoes erupted and the lava from the eruption cooled down. As it cooled down, it turned into a solid and formed the Earth’s surface. Almost all of the ocean floor and some continents are made out of volcanic rock! That is how 80% of the Earth’s surface was formed by volcanoes.