Earth's Formation and Interior

Earth’s Formation and Structure

• Earth formed approximately 4.6 billion years ago, along with other planets, from the Nebula Theory.
• Early Earth, known as Proto-Earth, was a molten, hot body that grew through accretion of smaller celestial bodies and cosmic dust.
• Earth is a terrestrial planet, one of the four in our solar system, and is the largest of the terrestrial planets.
• Earth's shape is described as a geoid, with a diameter exceeding 12,000 km.

Earth's Interior Observation Methods

• Direct observation of Earth's interior is limited, with mining galleries reaching a depth of 2,500 meters, oil and water wells reaching up to 10 km in rare cases.
• Seismic investigation is the primary tool for studying the Earth's interior, using waves generated by earthquakes or controlled blasts.
• Seismic waves travel through different layers of the Earth, revealing information about their composition through reflection and refraction.
• Reflection occurs when waves return to the surface due to boundaries between different layers, while refraction is the bending of waves as they pass through layers with different properties.
• Natural events like earthquakes, volcanoes, and tsunamis produce powerful seismic waves that travel throughout the Earth, while artificial seismic waves are weaker and have a shorter travel distance.

Earthquakes and Seismic Waves

• The origin point of an earthquake inside the Earth is called the hypocenter, with the area directly above it on the surface called the epicenter.
• Hypocenters can be as shallow as 100 km or as deep as 600-700 km below the surface.

Seismic wave types:

• Body waves: Travel through the Earth's interior.
  • Primary waves (P-waves): Fastest waves; travel through solids and liquids by compressing and expanding the medium.
  • Secondary waves (S-waves): Travel only through solid media; propagate by shearing the medium.
• Surface waves: Travel along the Earth's surface.
  • Love waves (L-waves): Move horizontally, causing the ground to shake from side to side.
  • Rayleigh waves (R-waves): Propagate like ocean waves, causing the ground to move in an elliptical motion.

Earth's Interior Composition

• Crust: Thin, silicate-dominated outer layer; thinner under oceans and thicker under continents.
  • Oceanic crust: Composed primarily of iron and magnesium.
  • Continental crust: Contains lighter metals like aluminum, sodium, and potassium, with oxygen, sulfur, and carbon present.
• Mantle: Thickest layer, primarily composed of silicate minerals (containing silicon and oxygen). Represents 80% of Earth's volume.
• Core: Composed mainly of iron and nickel.
  • Outer Core: Liquid layer due to high temperatures and pressure.
  • Inner Core: Solid layer due to immense pressure, even though the temperature is extremely high.

Earth's Interior Physical Properties

• Lithosphere: Rigid, outermost layer comprised of the crust and upper mantle. Subdivided into tectonic plates that move relative to one another.
• Asthenosphere: Located beneath the lithosphere, also known as the upper mantle; behaves as a soft, semi-solid material that allows tectonic plates to move through convection currents.
• Mesosphere: Also known as the lower mantle, extends from 660 km to 2900 km below the surface; rocks are denser in this layer but still capable of slow movement.
• Outer Core: Liquid layer between 2900 km and 5170 km; responsible for generating the Earth's magnetic field.
• Inner Core: Solid layer at the very center of the Earth; composed primarily of iron and nickel, and rotates independently of the Earth's rotation.

Major Lithospheric Plates

• North American Plate
• Eurasian Plate
• African Plate
• South American Plate
• Australian-Indian Plate
• Antarctic Plate
• Pacific Plate (only plate entirely composed of oceanic crust)