Lecture 4

Question 1

Hadeon eon

Answer 1

“Hellish”
Planets just formed and still many planetoids
Heavy bombardment period

Question 2

Late heavy bombardment

Answer 2

Caused by re-arrangement of planetary orbits during Hadeon eon
Late planetismals swallowed by planets

Question 3

Earth structure

Answer 3

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).

Question 4

Differentiation

Answer 4

Separation of minerals by density

Heavy sink, lighter rise

Question 5

Sources of heat in earth causing differentiation

Answer 5

1. Impacts
2. Gravitational energy in centre
3. Radioactive decay of elements (Currently what keeps interior hot)

Question 6

Processes caused by earth’s interior heat

Answer 6

1. Volcanism: Release of gas trapped in interior and extrusion of igneous rock.
2. Plate tectonics: Movement + recycling of rocks.
3. Magnetic field: Shielding of atmosphere from cosmic energetic particles.

Question 7

Escape velocity

Answer 7

More massive bodies = Larger escape velocity = Harder for gas to escape

(If planet too hot, light atoms will evaporate and fly out of atmosphere)

Question 8

Solar wind

Answer 8

Strips off atmosphere with energetic particles from Sun.

Earth has magnetic field to protect atmosphere.

Question 9

What is found in Earth’s atmosphere?

Answer 9

Nitrogen
Oxygen 
Water vapour
Argon
Carbon dioxide

Question 10

Where is the earth’s magnetic field generated?

Answer 10

Core

Rapid rotation of metals causes electric current

Question 11

Requirements for magnetic field

Answer 11

1) Molten, metallic (conductive) core
2) Rapid or moderately rapid rotation
3) Convection within globe

Question 12

Tectonic plates

Answer 12

Moved by convection motions in mantle

Moves few cm per year

Question 13

Continental drift

Answer 13

Alfred Wagner

Used to be one big continent

Question 14

Subduction zone

Answer 14

Where seafloor crust material sinks under plates

Important for auto-regulation of climate

Question 15

Seafloor crust and continental crust

Answer 15

Seafloor crust: High density, heavy igneous rock (basalt), 5-10 km thick

Continental crust: Low density, light rocks (granite), 20-70 km thick

Question 16

Why no plate tectonics on Mercury, Venus and Mars?

Answer 16

• High surface temp may have baked out water from crust

- Thicker crust may resist fracturing

Question 17

Greenhouse effect

Answer 17

Greenhouse gases trap and absorb infrared radiation leaving surface
(CO2 absorbs and spits out IR light, which warms up atmosphere)

Question 18

Positive or negative feedback?

More greenhouse gases -> Hotter atmosphere -> More greenhouse gases released from oceans

Answer 18

Positive

Question 19

Positive or negative feedback?

More snow snd ice -> Cooler atmosphere -> More snow and ice

Answer 19

Positive

Question 20

Positive or negative feedback?
Hotter surface temp -> More water vapour -> More clouds -> More sunlight reflected back into space -> Cooler surface temp

Answer 20

Negative

Question 21

CO2 cycle

Answer 21

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)

Question 22

How does temp affect CO2 cycle?

Answer 22

High temp -> Faster weathering -> Strong CO2 removal

Low temp -> Weaker weathering -> Atmospheric CO2 buildup

(Negative feedback)

Question 23

Weakness of CO2 cycle

Answer 23

1) Has delay time of 400,00 years
2) Very slow, possibly taking millions of years
3) Prone to instabilities

Question 24

Snowball Earth

Answer 24

• Happened 2.4-2.2 Gyr and 750-580 Myr ago

- Glaciers went down to equator and oceans froze 1 km deep

Question 25

Hypothesis for 2nd snowball earth

Answer 25

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