Class #3 -- Geology 117Class #3 -- Geology 117

EARTH 2: EARTH 2: Structure, origin, ageStructure, origin, age

•Internal zonesInternal zones

•Age of EarthAge of Earth

•Origin of the oceans and atmosphereOrigin of the oceans and atmosphere

•Important events in Earth historyImportant events in Earth history

Layering of the Earth Based onRigidity

Layer Depth (km) Rigidity

Lithosphere 150 beneath continents Rigid70 beneath oceans (elastic)

(includes some mantle!)

Asthenosphere Bottom of Lithosphere to Ductile about 250 km (plastic)

Rest of Mantle Bottom of Asthenosphere Ductile, to the core but stronger

Layering in the earth (based on rigidity)

The Mantle is NOT LIQUID

• Maybe small amounts of liquid in tiny pores in the asthenosphere, BUT ~99%+ solid

• BUT…Mantle is plastic over long distances and time, very slowly “creeping” to change shape

http://www.extremeicesurvey.org/index.php/new_gallery/timelapse_1/

Solids can flow very slowly

•Early H2 and He (light gases)-- “blown away”

•Release of gases from interior N2, CO2, CH4, NH3, H2S, HCl, H2O vapor.

•Evolution of atmosphere: (a) loss of reactive gases; (b) development of life – much later...

CO2 removed and O2 accumulated.

Origin of Atmosphere

•Formed very early in earth history

•Cooling; condensation of water vapor

•Acid rain: from acid gases in atmosphere

•Reaction with surface rocks to form dissolved products and sediments

•Little change in oceans through time:

-- Salinity and area remained ~ constant-- depth and volume increased a little

Origin of Oceans

Geologic Time Scale •based on record in rocks of "events"

•mountain building•fossil evolution

•radiometric dating gave "absolute" ages (in years).

Earth History

Geologic Time Scale: Fig. 1.24

Important events:•Origin of Earth: 4,600 m.y.•Appearance of "oceans": ~4,400 m.y.•Oldest preserved rock on continents: 4,200 m.y.•First bacteria: ≥3,800 m.y.•Photosynthesizing algae appear: ~3,000 m.y.•O2 in the atm.: ~2,000 m.y.•Multicellular organisms: ~600 m.y.•First "hominids": ~4 m.y.

Earth History

Represents amount of lead

Represents amount of uranium

•O2 NOT present before life evolved!!!

•Photosynthesis can generate O2

•Need carbon- use CO2 from atmos.•Remove the O’s, use the C’s•Build living tissues with C-rich organic matter•Waste Product: O2

•Builds up only if organic matter is buried

•Initially toxic to life

•Eventual adaptation- led to higher organisms?

Oxygen in the atmopshere

Fig. 1.20

Fig. 1.19