Most of the Earth surface, about 70%, is covered with water. The remaining 30% is made up of the seven continental landmasses. Underneath the water that fills the oceans, and the dirt and plants that cover the continents, the Earth’s surface layer is made of rock. This outer layer formed a hard, rocky crust as lava cooled about 4.5 billion years ago. This crust is broken into many large plates(tectonic plates) that move slowly relative to each other. The mountain ranges around the world formed when two plates collided and their edges are forced up. Many other surface features are the result of the movement of these tectonic plates. The plates move anywhere from 25 to 100 mm per year. About 250 million years ago most of the land was connected together.
The rocky layer under the soil of the Earth is called the crust. This comprises the continents and ocean basins. The crust has a variable thickness, being 35-70 km thick on the continents and 5-10 km thick in the ocean basins. The crust is composed mainly of alumino-silicates. The entire crust occupies just 1% of the Earth’s volume. The temperature of the crust increases as you go deeper into the Earth. It starts out cool, but can get up to 400 degrees C at the boundary between the crust and the mantle.