We live on the outermost layer of Earth, called the crust. This varies in depth between 5 and 75 km. It’s mostly made of silicates, with a tremendous amount of oxygen mixed in. In fact, 47% of the Earth’s crust is oxygen. The thickest parts of the crust are under the continents, and the thinnest parts are underneath the oceans. Beneath this crust is the mantle, which goes down to a depth of 2890 km. It’s the largest layer on Earth, and mostly consists of silicate rocks rich in iron and magnesium.