which elements make up the crust?
The thickest parts are under the continents and the thinnest parts are under the oceans. Crust. Earth's crust is made up of several elements: oxygen, 47 percent; silicon, 27 percent; aluminum, 8 percent; iron, 5 percent; calcium, 4 percent; magnesium, potassium and sodium, 2 percent. The crust is divided into huge plates that float on the mantle, the next layer.