Notes on the Formation and Structure of Planet Earth

Introduction

• Planet Earth: Home to all known life in the universe.
• Age: About a third of the universe's age, 4.6 billion years old.
• Structure: A sphere with a heavy metal core and lighter crust, enveloped in an atmosphere.

Formation of Earth

• Formed from remnants of dead stars in a dirty gas cloud.
• Process: Accretion disk formation, particle clumping leading to planet formation.
• Duration: 10 to 20 million years.
• Early Collision: Mars-sized object collision formed the Moon.

Early Earth Conditions

• Initially a hot, chaotic environment with frequent asteroid impacts.
• Surface water emerged and evaporated repeatedly.
• Asteroids contributed additional water.

Water Distribution

• Earth's surface: 71% water, 29% land.
• Water types:
  • 97.5% saline water
  • 2.5% fresh water
• Fresh water composition:
  • 69% ice and snow
  • 30% groundwater
  • 1% lakes, rivers, and living organisms

Geological Activity

• Plate Tectonics: Movement of Earth's crust, forming mountains and trenches.
  • Highest point: Mount Everest.
  • Deepest point: Mariana Trench.
• Earth's crust: 5 to 70 km thick.

Earth's Internal Structure

• Mantle:
  • Silicate rocky shell, ~2,900 km thick
  • Upper mantle includes lithosphere and asthenosphere
• Core:
  • Outer core: Liquid iron and nickel, 2,266 km thick, temperatures 4,000°C to 5,700°C
  • Inner core: Solid iron-nickel ball, 1,200 km radius, temperature similar to the Sun's surface.

Earth's Magnetic Field

• Protects Earth from solar and cosmic radiation.
• Generated by electrical currents in the core, known as the dynamo effect.

Atmosphere

• Composition: Mostly nitrogen, oxygen, argon, carbon dioxide, and water vapor.
• Layers:
  • Troposphere: Lowest layer with weather, ~12 km thick
  • Stratosphere: Contains ozone layer
  • Mesosphere: Coolest region
  • Thermosphere: Transition to space, contains ionosphere and ISS
  • Exosphere: Outermost layer, extends to 10,000 km, merges with space

Human Presence

• Humans have existed for 200,000 years, a tiny fraction of Earth's history.
• Earth is a small, wet rock, the product of cosmic processes.
• Life on Earth is a result of chance, universal laws, and random events.