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.