1: Earth structure and plate tectonics

Question 1

The Earth: Radius, average density, average composition, age

Answer 1

Radius - 6371 km
Density - 5.5g/cm^3
Composotion - Iron (35%), Oxygen (30%), Silicon (15%), Magnesium (13%), Other (7%)
Age - 4.56 billion years

Question 2

Earth compositionally heterogenous and layered

Answer 2

Core, mantle, crust

Question 3

How did scientist discover the core?

Answer 3

• Because of earthquakes
• seismic wave bend (refract) as they encounter density interfaces
• some wave that pass through the core are refracted substantially, indicating something really dense is down there
• some types of seismic waves cannot travel through liquids, indicating that at least the outer part of the Earth’s core is liquid.

Question 4

Inner Core (max density, temp, solid or liquid?)

Answer 4

• Density: ~ 13 g/cm^3
• Max Temp - 4300 C
• Solid, mostly Fe + Ni

Question 5

Outer Core (temp at top, convects, solid or liquid?)

Answer 5

• Temp: 3700 C
• liquid, mostly Fe + Ni
• Convection flows

Question 6

Mantle (% of earth’s volume)

Answer 6

• 83%
• most is solid rock, only a few percent melt in uppermost part
• peridotite containing Fe-Mg rich silicate minerals (olivine and pyroxene)

Question 7

Deep Mantle

Answer 7

• the part below ~ 100 km

- totally solid, but convection occurs over geological time scales

Question 8

Continental crust (how thick, density, composite, age)

Answer 8

• 20-70 km thick
• ~ 2.5 g/cm^3
• compositionally diverse
• Si + Al rich minerals (e.g. quartz and feldspars)
• Age: 0 - >4 billion years old

Question 9

Oceanic Crust (thickness, density, composite, minerals, age)

Answer 9

• 5-10km thick
• 3 g/cm^3
• compositionally homogeneous
• basaltic
• 0-200 million years old

Question 10

Lithosphere

Answer 10

• the portion of the Earth that behaves rigidly
• does not convect
• crust + uppermost mantle
• sits on top of a layer of particularly non-rigid, partially molten layer of mantle (asthenophere)

Question 11

About how many lithospheric plates are there?

Answer 11

About 13

Question 12

Lithospheric plates movements

Answer 12

• move relative to one another at rates of a few cm/yr

- boundaries defined by zones of seismic activity

Question 13

Type of plate boundaries

Answer 13

Divergent, Convergent, Transform

Question 14

Divergent

Answer 14

constructive - oceanic lithosphere is produced by partial melting in upwelling mantle; large amounts of basalt magma produced
ex. mid-ocean ridges, including iceland

Question 15

Convergent

Answer 15

• destructive: oceanic lithosphere sinks back down into the mantle
• subduction zones, deep sea trenches
• earthquakes and volcanoes common
  ex. cascades, japan, andes

Question 16

Transform

Answer 16

• conservative: lithospheric plates slide past each other
• earthquakes common
  ex. San Andreas Fault (Cali)

Question 17

Geological evidence for plate tectonics

Answer 17

Supercontinental breakup

Question 18

Evidence for supercontinental breakup?

Answer 18

• Fit of the continents
• Locations of ancient glaciations
• distribution of terrestrial fossils
• matching rock units and mountain belts

Question 19

Seafloor spreading: Ocean crust varies in age in regular patterns consistent with:

Answer 19

• generation of new ocean crust at mid-ocean ridges
• subsequent movement away from the MOR’s
• destruction of old ocean crust at subduction zones

Question 20

Define: Hotspots

Answer 20

large volcanic centers produced by long-lived partial melting in the mantle

Question 21

Define: Hotspot track

Answer 21

volcanic chains produced by the motion of a lithospheric plate over a “stationary” hotspot deep in the mantle

Question 22

Modern ___ measurements are consistent with geologic predictions of ____ ____

Answer 22

GPS; plate motions

Question 23

Convection Flows

Answer 23

currents of molten iron produces Earth’s magnetic field