Water; - delivered by comets 4.5 Byr ago

Comets delivered the volatiles (primarily water) to the innerplanets some 4 billion years ago, just after the formation of thesolar system.

Close up picture of the nucleus of comet Halley fromGiotto spacecraft

The extensive impact craters created early on during the formation of the solar system has been eradicated on Earth by weathering.

Atmosphere, weather driven by the Sun

Abundances of the Elements

Volcanoes

The Carbon Cycle

Carbon Dioxide (CO2) is a major constituent of the atmospheresof both Mars and Venus, but not the Earth - Why?

Volcanoes outgas CO2 which dissolves in rainwater,is washed into the oceans and combines with sea-shellsto become carbonates.

Plants also utilize CO2 in photosynthesis producing O2

This carbon cycle does not operate on Mars or Venus.

The presence of Life

Regulates the amount of Oxygen (O2)

Plants photosynthesize CO2 into O2, and N2

Greenhouse Effect

Carbon Dioxide

Global Warming?

Internal Structure resulting from Chemical Differentiation

Plate Tectonics

Earth’s Major Plates

Collision of two plates

Geology - Igneous ( molten ) rocks

Geology - Sedimentary (layered) rocks

Metamorphic Rocks - modified by extreme temperaturesand pressures deep within the Earth’s crust

The Earth’s Magnetic Field

Protects Life on Earth from damaging Cosmic Rays

Aurora