Largest Terrestrial planet

Metallic core, silicate crust

Active plate tectonics and volcanoes

• What is the source of the energy which powered the lava flooding?

Rich, thick atmosphere

• Primeval (initial) atmosphere rich in carbon dioxide (CO₂), nitrogen (N₂), water (H₂O)
• Why not primarily hydrogen, methane, and ammonia like the solar nebula?
• Where did the carbon dioxide go?
• Why is this critical? (greenhouse effect)
• Where did the hydrogen (H), methane (CH₄), and ammonia (NH₃) go?
• Why is this critical? (UV light, ozone layer)
• Where did the free oxygen come from?
• Why is this critical? (do you like breathing?)
• Does life (plants – photosynthesis, animals – methane, people – fossil fuels, CFCs) alter our atmosphere?

Why is the cratering record obscured?

• Atmosphere protects
• Plate tectonics reform crust

	Antarctica	Australia	Mount Etna - Sicily	Cassiar Mountains
	Strait of Gibraltar	Mississippi River	Grand Canyon	Wadi Kufra - Libya
Images showing the wide variety of environments found across planet Earth. [NASA]