Lecture 4 Flashcards
Hadeon eon
“Hellish”
Planets just formed and still many planetoids
Heavy bombardment period
Late heavy bombardment
Caused by re-arrangement of planetary orbits during Hadeon eon
Late planetismals swallowed by planets
Earth structure
Core: Dense, iron and nickel core. Molten outside.
Mantle: Silicates and less dense rocks with pockets of partly molten rocks. Most of earth’s volume.
Crust/lithosphere: Outer skin consisting of igneous rocks (granite and basalt).
Differentiation
Separation of minerals by density
Heavy sink, lighter rise
Sources of heat in earth causing differentiation
- Impacts
- Gravitational energy in centre
- Radioactive decay of elements (Currently what keeps interior hot)
Processes caused by earth’s interior heat
- Volcanism: Release of gas trapped in interior and extrusion of igneous rock.
- Plate tectonics: Movement + recycling of rocks.
- Magnetic field: Shielding of atmosphere from cosmic energetic particles.
Escape velocity
More massive bodies = Larger escape velocity = Harder for gas to escape
(If planet too hot, light atoms will evaporate and fly out of atmosphere)
Solar wind
Strips off atmosphere with energetic particles from Sun.
Earth has magnetic field to protect atmosphere.
What is found in Earth’s atmosphere?
Nitrogen Oxygen Water vapour Argon Carbon dioxide
Where is the earth’s magnetic field generated?
Core
Rapid rotation of metals causes electric current
Requirements for magnetic field
1) Molten, metallic (conductive) core
2) Rapid or moderately rapid rotation
3) Convection within globe
Tectonic plates
Moved by convection motions in mantle
Moves few cm per year
Continental drift
Alfred Wagner
Used to be one big continent
Subduction zone
Where seafloor crust material sinks under plates
Important for auto-regulation of climate
Seafloor crust and continental crust
Seafloor crust: High density, heavy igneous rock (basalt), 5-10 km thick
Continental crust: Low density, light rocks (granite), 20-70 km thick
Why no plate tectonics on Mercury, Venus and Mars?
- High surface temp may have baked out water from crust
- Thicker crust may resist fracturing
Greenhouse effect
Greenhouse gases trap and absorb infrared radiation leaving surface
(CO2 absorbs and spits out IR light, which warms up atmosphere)
Positive or negative feedback?
More greenhouse gases -> Hotter atmosphere -> More greenhouse gases released from oceans
Positive
Positive or negative feedback?
More snow snd ice -> Cooler atmosphere -> More snow and ice
Positive
Positive or negative feedback?
Hotter surface temp -> More water vapour -> More clouds -> More sunlight reflected back into space -> Cooler surface temp
Negative
CO2 cycle
1) Atmospheric CO2 dissolves in rain water
2) Acidic rain erodes and dissolves rocks. Minerals (silicate) carried by rivers to oceans
3) Dissolved oceanic CO2 reacts w/ silicate rocks to form carbonate rocks
4) Carbonate rocks pushed into mantle and heated in subduction zones. Gases (CO2) released back into atmosphere by volcanoes.
5) Back to 1)
How does temp affect CO2 cycle?
High temp -> Faster weathering -> Strong CO2 removal
Low temp -> Weaker weathering -> Atmospheric CO2 buildup
(Negative feedback)
Weakness of CO2 cycle
1) Has delay time of 400,00 years
2) Very slow, possibly taking millions of years
3) Prone to instabilities
Snowball Earth
- Happened 2.4-2.2 Gyr and 750-580 Myr ago
- Glaciers went down to equator and oceans froze 1 km deep
Hypothesis for 2nd snowball earth
Continental drift happened to gather all continents near equator
Weathering could continue despite glaciers (more CO2 removal)
Weak greenhouse effect (low CO2) and lots of glaciers (reflection)
Become positive feedback
