Our Atmosphere

Our AtmosphereJennifer PogueMarch 6, 2012OriginThe earliest atmosphere was believed to be Hydrogen and HeliumWhy? They were the most abundant gases of the universe.Methane and ammonia were also found in high concentrations.Where did it go?It escaped into space.

Why?Earths gravity was too weak to hold the light gases in place.

The Second AtmosphereSteam vents and volcanoes vented gases which collected in the atmosphere**We are assuming the gases vented by volcanoes then is the same as the gases now.Water vapor (80%), carbon dioxide (10%), nitrogen (~5%)How did the composition change?CO2 Locked into sedimentary rocks, i.e. limestoneH2Ocondensed to form the ground water or cloudsThe concentration of CO2 and H2O decreased leaving N2 to increase in concentration .Nitrogen is relatively inactive chemically.Oxygen increased as plants converted carbon dioxide through photosynthesis.

Proof is in the rocksPrecipitation of limestone in great quantities.The oxidation of iron to form banded deposits in early rocks.The distribution of various minerals in most early sedimentary rocks.

Evidence of an Early Atmosphere Banded-iron

Limestone

(Stone Museum)(Stone Museum)Todays Composition We have lots more oxygen (~21%) and lots less carbon dioxide.Both of these are good thingsComposition Comparison78%Nitrogen4-6%21%Oxygen