3. Water; - delivered by comets 4.5 Byr ago

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

5. Close up picture of the nucleus of comet Halley from Giotto spacecraft

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

7. Atmosphere, weather driven by the Sun

9. Abundances of the Elements

11. Volcanoes

12. The Carbon Cycle Carbon Dioxide (CO 2 ) is a major constituent of the atmospheres of both Mars and Venus, but not the Earth - Why? Volcanoes outgas CO 2 which dissolves in rainwater, is washed into the oceans and combines with sea-shells to become carbonates. Plants also utilize CO 2 in photosynthesis producing O 2 This carbon cycle does not operate on Mars or Venus.

13. The presence of Life Regulates the amount of Oxygen (O 2 ) Plants photosynthesize CO 2 into O 2, and N 2

14. Greenhouse Effect

15. Carbon Dioxide

16. Global Warming?

17. Internal Structure resulting from Chemical Differentiation

21. Plate Tectonics

22. Earth’s Major Plates

23. Collision of two plates

25. Geology - Igneous ( molten ) rocks

26. Geology - Sedimentary (layered) rocks

28. Metamorphic Rocks - modified by extreme temperatures and pressures deep within the Earth’s crust

29. The Earth’s Magnetic Field

30. Protects Life on Earth from damaging Cosmic Rays

31. Aurora