Lecture Notes: Planet Earth and Its Formation

Introduction

• Earth is the home of all known life forms in the universe.
• Earth is a slightly squashed sphere with a metal core and a lighter crust.
• Covered by an atmosphere, vast oceans, and various landscapes like mountains and rivers.

Formation of Earth

• Age: Approximately 4.6 billion years.
• Formed from remnants of dead stars in a large gas cloud.
• The gas cloud formed an accretion disk, leading to planet formation over 10-20 million years.
• Early Earth experienced violent collisions, including a significant impact forming the Moon.

Early Earth Conditions

• Initially, a hot, hostile environment with asteroid impacts and lava seas.
• Gradually cooled, allowing water to surface and form oceans.
• Asteroids contributed additional water.

Earth's Water

• Earth's surface: 71% water, 29% land.
• 97.5% of water is saline; 2.5% is fresh.
  • 69% of fresh water is in ice/snow.
  • 30% is groundwater.
  • 1% is in lakes, rivers, and living organisms.

Plate Tectonics

• Earth's crust is dynamic, consisting of moving plates.
• Plate interactions form mountains like Mount Everest and trenches like the Mariana Trench.

Earth's Structure

• Crust: 5-70 km thick.
• Mantle: 2,900 km thick, consists of:
  • Upper Mantle (lithosphere and asthenosphere).
  • Lower Mantle leading to the outer core.
• Core:
  • Outer Core: Liquid iron and nickel, 2,266 km thick.
  • Inner Core: Solid iron-nickel alloy, 1,200 km radius.

Earth's Magnetic Field

• Generated by electrical currents in the core.
• Provides a stable environment by diverting high-energy solar particles.

Earth's Atmosphere

• Composed mainly of nitrogen, oxygen, argon, carbon dioxide.
• Layers:
  • Troposphere: Weather layer, 12 km thick.
  • Stratosphere: Contains ozone layer.
  • Mesosphere: Coldest layer.
  • Thermosphere: Transition to space starts here.
  • Exosphere: Merges with outer space, up to 10,000 km.

Human Perspective

• Humans have existed for 200,000 years, a minuscule fraction of Earth's history.
• Earth is a product of universal processes, a result of constant creation and destruction.
• Humans reside in a thin, moist layer on the planet's surface.

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These notes summarize the formation, structure, and significance of Earth, highlighting its dynamic history and current state as a home for life.