The elements largely composing the rock and soil on Earth's surface are oxygen, silicon, iron and magnesium. Water, covering about 70 percent of Earth's surface, is composed largely of hydrogen, oxygen, sodium, chlorine and magnesium. There are also small or trace quantities of other elements on Earth's surface, including calcium, nickel, aluminum and gold.
Oxygen is the most common element found on the Earth's surface, composing almost one-half of the mass of its crust. Silicon is the second most abundant element. It is found in soil and largely composes the quartz-feldspar minerals present in igneous and metamorphic rock. Feldspar is the most abundant mineral present on Earth behind quartz and composes approximately 60 percent of Earth's crust.
Pure water is made up of two atoms of hydrogen per one atom of oxygen. However, the water on Earth does not contain twice as much oxygen as hydrogen, because there are large amounts of dissolved oxygen atoms in water. The Earth's ocean also contains large amounts of salt, which is composed of sodium and chlorine.
The atmosphere of the Earth is made up of five principal layers, which are called the exosphere, mesosphere, stratosphere, thermosphere and troposphere. These layers are composed largely of oxygen, nitrogen and argon.