Earth's Origin and Internal Structure

Origin of the Earth

• The Solar System, including the Sun and planets, formed from a solar nebula, which also formed the "Proto-Earth".
• The nebular material in Proto-Earth was uniform, with no stratification.
• Meteors and asteroids impacted Proto-Earth, causing gravitational compression.
• As the Earth cooled and coalesced, heavier materials like iron and nickel migrated to the center, while lighter materials like silicon, oxygen, aluminum, and potassium remained near the surface, resulting in a density-stratified planet.

How Do We Study the Earth's Interior

• By drilling into the Earth's deep, with the deepest hole being about 12 km (less than 0.2% of the distance from the surface to the center).
• By studying and measuring the travel times of earthquake waves to seismograph stations.
• Earthquake waves are categorized into two types: Surface waves, which travel near the surface, and Body waves, which travel deep into the Earth.

Body Waves

• There are two types of body waves: P-waves (Primary waves) and S-waves (Secondary waves).
• P-waves are compressional waves that are the fastest of seismic waves, can move through solid rock and fluids, and travel horizontally through a medium by compression and dilation.
• S-waves are slower than P-waves, can only move through solid rock, and move rock particles up and down or side-to-side, perpendicular to the direction of travel.

Earth's Structure

Crust

• Continental Crust: 35 km thick, up to 75 km thick under mountains, and composed of felsic (Si-rich) to mafic (Fe-Mg rich) materials.
• Oceanic Crust: thinner and denser than Continental Crust.

Other Layers

• Mantle
• Core
• Geomagnetism