1. Earths Early History
Looking into the past: Stars and rocks, both show what has been
LAND ENVIRONMENTS
Earth Formed approx. 4.6 Billion Years Ago (BYA)
Gravity pulls heavier elements into the core
Intense heat
Molten rock
Asteroid impacts
500 million years pass and an solid outer core forms

2. ATMOSPHERE
Now 300 mile thick layer protecting us from space
Exact historical composition unknown
Volcanoes responsible for early atmosphere so:
Atmospheric gases inferred from modern volcanic gasses, including:
water vapor
CO2,
sulfur dioxide (SO2)
Carbon monoxide (CO)
Hydrogen sulfide (H2S)
Hydrogen cyanide (HCN)
Nitrogen (N2)
Hydrogen (H2)
Little or no free oxygen

3. Over millions of years
Earth cooled
Liquid water formed
Life appeared about 500 million years after the first oceans formed
Earliest evidence of life – 3.5 BYA