EARTH & LIFE SCIENCE

Theories on the Origin of the Solar System

• Nebular hypothesis

  - The solar system formed from a spinning cloud of gas and dust.

  - As it collapsed, it formed the Sun in the center and planets around it.

  - Explains why all planets orbit in the same direction.

• Protoplanet hypothesis

  - Small space rocks (planetesimals) bumped into each other and stuck together.

  - Over time, they grew into protoplanets (early planets).

  - Inner planets (like Earth) formed from rock and metal.

  - Outer planets formed from gas and ice.

• Collision hypothesis

  - A star passed close to the Sun and pulled material off of it.

  - That material became the planets.

  - Problem: Doesn’t explain why planets move in almost perfect circles.

• Accretion shock theory

  - A supernova (exploding star) nearby sent a shockwave through space.

  - This shockwave caused a cloud of gas and dust to collapse, forming the Sun and planets.

Features of the Solar system

Sun and Mass Distribution

• Sun holds most of the Solar System's mass.

• Outer planets hold most of the angular momentum (spin and orbital motion).

Planetary Orbits

• Planets move in elliptical (oval-shaped) orbits.

• All orbits lie roughly on the same flat plane.

Revolution Periods (Orbit Time)

• Closer planets to the Sun orbit faster.

• Farther planets orbit slower.

  • Example: Mercury orbits quickly, Neptune orbits slowly.

Small-Scale Features

🧭 Planets

• Not fixed like stars – they move across the sky.

• Historically believed to influence events (astrology origins).

Dwarf Planets

• Smaller bodies that orbit the Sun, but not dominant in their orbits (e.g. Pluto).

• Not included in either terrestrial or gas giant categories.

Rotation of Planets

Prograde Rotation

• Rotates in the same direction as the Sun (counterclockwise).

• Most planets (including Earth) rotate this way.

Retrograde Rotation

• Rotates in the opposite direction.

• Venus and Uranus rotate retrograde.

  • Likely caused by massive impacts early in their history.

Kepler’s Laws of Planetary Motion

1. Law of Ellipses

   • Planets orbit the Sun in ellipses, not perfect circles.

   • The Sun is at one focus of the ellipse.

2. Law of Equal Areas

   • Planets move faster when closer to the Sun (perihelion) and slower when farther (aphelion).

   • A planet sweeps out equal areas in equal time.

3. Law of Harmonies

   • The farther a planet is, the longer it takes to orbit the Sun.

   • Formula: P2∝a3P^2 \propto a^3P2∝a3 (orbital period squared is proportional to distance cubed).

🌍 Planetary Habitability

Factors needed for a planet to support life:

• Atmosphere – Controls temperature and blocks harmful radiation.

• Water – Essential for life; it's a universal solvent.

• Temperature – Must be right for liquid water to exist (in the habitable zone).

• Light Energy – Needed for photosynthesis.

• Nutrients – Elements like nitrogen and phosphorus support life processes.

🌎 Earth’s Subsystems & Interactions

• Geosphere – Includes:

  • Crust & Mantle (solid rock),

  • Outer Core (liquid metal),

  • Inner Core (solid metal).

  • It's the solid part of Earth, interacting with other systems like the atmosphere and biosphere.

Earth’s Subsystems & Interactions (Simplified)

Geosphere

• Solid Earth: crust, mantle, liquid outer core, solid inner core.

• Provides land, rocks, minerals, and supports Earth's structure.

🌬 Atmosphere

• Earth’s invisible blanket of gases.

• Regulates temperature, protects from space debris and radiation.

💧 Hydrosphere

• All water on Earth: oceans, rivers, lakes, groundwater, and water vapor.

• Supports life and drives the water cycle and weather systems.

🌱 Biosphere

• All living organisms on Earth.

• Includes interactions between life forms and the environment (air, water, soil).

❄ Cryosphere

• Frozen parts of Earth: glaciers, icebergs, permafrost, frozen lakes/rivers.

• Affects sea level and climate.

🧲 Magnetosphere

• Area around Earth controlled by its magnetic field.

• Shields Earth from solar wind and cosmic radiation.