Earth's Atmosphere and Composition

Composition of the Atmosphere

• The atmosphere is composed of gases including nitrogen, oxygen, argon, water, carbon dioxide, neon, ozone, helium, methane, krypton, hydrogen, and nitrogen dioxide.
• Carbon monoxide is also present in the atmosphere.

Chemical Composition of the Earth

• The overall composition of the Earth is dominated by iron (Fe), oxygen (O), silicon (Si), magnesium (Mg), nickel (Ni), and sulfur (S).
• The Earth's composition is similar to that of meteorites, suggesting it formed from planetesimals composed of metallic iron and silicates.

Bulk Composition of the Earth

• Iron (Fe) makes up 34.6% of the Earth's composition.
• Oxygen (O2) makes up 29.5% of the Earth's composition.
• Silicon (Si) makes up 15.2% of the Earth's composition.
• Magnesium (Mg) makes up 12.7% of the Earth's composition.
• Nickel (Ni) makes up 2.4% of the Earth's composition.
• Sulfur (S) makes up 9.0% of the Earth's composition.
• Titanium (Ti) makes up 0.05% of the Earth's composition.

Types of Rocks

• Igneous rocks are formed by cooling of magma.
• Sedimentary rocks are formed by consolidation of loose sediment or by chemical precipitation from water.
• Metamorphic rocks are formed by subjecting igneous or sedimentary rocks to high temperature and/or pressure.

The Earth's Internal Structure

• The Earth has a layered structure, as evidenced by seismology.
• Seismic waves travel through the Earth with velocities dependent on the type of wave and physical properties of the material.

Types of Seismic Waves

• Body waves travel in all directions through the body of the Earth.
• Surface waves differ from body waves, traveling along paths nearly parallel to the Earth's surface, and behave like S-waves.

The Earth's Core

• The core is thought to be divided into a solid inner core and a liquid outer core.
• The outer core is presumed to be liquid because it does not transmit shear waves and the velocity of compressional waves is sharply reduced.
• The inner core is considered to be solid because of the behavior of P and S waves passing through it.

The Crust

• The crust makes up only 0.5% of the Earth's total mass.
• The crust can be subdivided into two main parts: continental and oceanic.
• The oceanic crust covers approximately 61% of the Earth's surface, but only comprises 30% of the crustal mass.
• The continental crust is much thicker, up to 70 km.

Learn about the chemical composition of the Earth's atmosphere and the planet itself, including the gases and elements that make them up.