Earth’s crust contains an abundance of chemicals, elements, minerals, and rocks.
Though there was a time when oxygen was nonexistent, it is now the most common element. It makes up about 20 percent of the air in its gaseous form, but is also found in combination with other materials in the crust.
Nearly 50 percent of Earth’s crust is made up of combinations of oxygen with other substances.
Sand and rock is mostly silicon and oxygen, and there is plenty of sand and rock around. These make up about 28 percent of the crust. Most of the rock on Earth is granite, molten rock that has cooled slowly.
Aluminum, found in almost all natural clay in the world, makes up a little less than 9 percent of the crust. More than 4 percent of the crust is iron and 3.5 percent is calcium. The remaining 5.5 percent of the crust comes from another ten elements and traces of many others.
Earth is made up of several layers around a very dense, solid core. Scientists learn about the interior of Earth by studying vibrations from earthquakes.