Transcript Layer Depth (km) Rigidity

Class #3 -- Geology 117
EARTH 2: Structure, origin, age
•Internal zones
•Age of Earth
•Origin of the oceans and atmosphere
•Important events in Earth history
Layering of the Earth
Based on
Rigidity
Layering in the earth (based on rigidity)
Layer
Depth (km)
Rigidity
Lithosphere
150 beneath continents
70 beneath oceans
(includes some mantle!)
Rigid
(elastic)
Asthenosphere
Bottom of Lithosphere to
about 250 km
Ductile
(plastic)
Rest of Mantle
Bottom of Asthenosphere
to the core
Ductile,
but stronger
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
Solids can flow very slowly
http://www.extremeicesurvey.org/index.php/new
_gallery/timelapse_1/
Origin of Atmosphere
•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 Oceans
• 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
Earth History
Geologic Time Scale
•based on record in rocks of "events"
•mountain building
•fossil evolution
•radiometric dating gave "absolute" ages (in years).
Geologic Time Scale: Fig. 1.24
Earth History
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.
Represents amount of
uranium
Represents amount of
lead
Oxygen in the atmopshere
•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?
Fig. 1.20
Fig. 1.19