Earth's Atmospheres Flashcards
What caused the 1st atmosphere?
The accumulation of gas left over from the creation of the planets
What was the composition of the 1st atmosphere?
Silica, metals, & likely lots of H2 & He
How was the 1st atmosphere lost?
Earth was still hot from its creation, had a weak gravitational field due to small size, & had not developed a magnetic field. Theia then collided to blast the atmosphere into space
What caused the 2nd atmosphere?
The cooling of the planet following the collision of Theia, facilitated by the creation of oceans, initiation of tectonics, & high volcanic activity associated with warmer, thinner crust
What was the composition of the 2nd atmosphere?
Methane, ammonia, & other products of volcanism (H2O, CO2, N2O, O2, fluorocarbons, noble elements….)
What is the Faint Young Sun Paradox?
During the 2nd atmosphere the Earth should have been frozen due to the sun’s weakness, but remained fairly warm due to lower albedo & GHG accumulation
What is the Late Veneer Hypothesis?
The idea that asteroid bombardment brought CO2 & HO to the 2nd atmosphere. The Asteroid belt supplied rock matter & the Kuiper belt water, methane, ammonia, & dust
What caused the end of the 2nd atmosphere?
The condensation of oceans from rain once the climate cooled bellow 100°C. Gravity held water on the planet & tectonics allowed for exchange between surface & interior waters. Oxygen producing life then evolved to change the atmosphere
What created the 3rd atmosphere?
The Great Oxygenation Event
What is the evidence for the Great Oxygenation Event?
Earlier paleosols with low Fe due to anoxic weathering, dominance of volcanoes (can’t form oxygen), & the increase of O2 concentration c.2.4Ga
How are BIFs proxies for oxygenation?
BIFs precipitated from the oxidation of dissolved Fe. Once Fe was used up, oxygen could concentrate in the atmosphere, limiting BIF production
How did life impact the composition of the 2nd & 3rd atmospheres?
Evolution of microbes produced methane in 2nd atmosphere, whereas cyanobacteria evolved to produce oxygen in the 3rd atmosphere (shown in stromatolites)
