1. Class #3 -- Geology 117 EARTH 2: Structure, 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

2. Layering of the Earth Based on Rigidity

3. LayerDepth (km)Rigidity Lithosphere150 beneath continentsRigid 70 beneath oceans (elastic) (includes some mantle!) AsthenosphereBottom of Lithosphere to Ductile about 250 km(plastic) Rest of MantleBottom of AsthenosphereDuctile, to the corebut stronger Layering in the earth (based on rigidity)

7. 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

8. http://www.extremeicesurvey.org/index.php/new _gallery/timelapse_1/ Solids can flow very slowly

10. Early H 2 and He (light gases)-- “blown away” Release of gases from interior N 2, CO 2, CH 4, NH 3, H 2 S, HCl, H 2 O vapor. Evolution of atmosphere: (a) loss of reactive gases; (b) development of life – much later... CO 2 removed and O 2 accumulated. Origin of Atmosphere

12. 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

13. Geologic Time Scale based on record in rocks of "events" mountain building fossil evolution radiometric dating gave "absolute" ages (in years). Earth History

14. Geologic Time Scale: Fig. 1.24

16. 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. O 2 in the atm.: ~2,000 m.y. Multicellular organisms: ~600 m.y. First "hominids": ~4 m.y. Earth History

17. Represents amount of lead Represents amount of uranium

18. O 2 NOT present before life evolved!!! Photosynthesis can generate O 2 Need carbon- use CO 2 from atmos. Remove the O’s, use the C’s Build living tissues with C-rich organic matter Waste Product: O 2 Builds up only if organic matter is buried Initially toxic to life Eventual adaptation- led to higher organisms? Oxygen in the atmopshere

19. Fig. 1.20

20. Fig. 1.19