The outermost layer of the earth is called the "crust." It is the solid, rocky layer that forms the Earth's surface and varies in thickness from around 5-70 kilometers. The crust is composed of different types of rocks and minerals, and it is broken up into tectonic plates that move and interact with each other, causing earthquakes and volcanic activity. The crust is also the layer where all living things exist and where most of our natural resources are found, such as oil, gas, and minerals.