Overview
This lecture covers the nebular theory for the formation of the solar system and Earth, Earth's internal layering, and the development of Earth's atmosphere.
Formation of the Solar System (Nebular Theory)
- The solar system formed from a nebula, a diffuse, hot cloud of gas and dust.
- As the nebula cooled, it condensed, flattened, and began rotating, forming a disk about 5 billion years ago.
- A proto-sun developed at the center, starting fusion processes.
- Accretion occurred as particles collided and stuck together, forming protoplanets.
- Protoplanets differentiated, with heavier materials moving to their centers and lighter materials toward the surface.
- The solar system formed with one sun and planets orbiting in the same plane; inner planets are rocky, and outer planets are gas giants.
Formation and Differentiation of Early Earth
- Early Earth formed as a homogeneous planetesimal from accreted material.
- Over time, Earth’s heavier elements migrated inward, forming a core, with lighter elements forming the mantle and crust (internal stratification).
- The first solid Earth crust appeared around 4.6 billion years ago, matching mineral dating.
Formation of the Moon
- About 4.4 billion years ago, a Mars-sized body collided with the hot early Earth.
- Debris from this impact formed the Moon, while some material was absorbed by Earth.
Development of Earth's Atmosphere
- Early Earth had no atmosphere due to solar wind blowing gases away.
- As the sun cooled, volcanic outgassing released gases, and Earth’s gravity retained them to form an atmosphere.
- Early atmosphere was rich in water vapor and carbon dioxide (CO2).
- Photosynthetic life, such as stromatolites, began adding oxygen to the atmosphere by about 2.5 billion years ago.
Key Terms & Definitions
- Nebula — a diffuse cloud of gas and dust in space.
- Accretion — growth by collision and sticking together of particles.
- Differentiation — process where heavier materials sink toward a planet's center, forming layers.
- Volcanic outgassing — release of gases from Earth’s interior through volcanoes.
- Stromatolites — layered structures formed by photosynthetic microorganisms.
Action Items / Next Steps
- Watch additional videos on Earth's internal layering for deeper understanding.