layers of the earth

Question 1

max direct observation of Earth’s interior

Answer 1

Kola Superdeep Borehole (12.3km)

Question 2

compositional layers

layers based on density / chemical composition

Answer 2

crust, mantle, core

layers are ordered, and from least dense to most dense

Question 3

propogation of seismic activity

P - wave

Answer 3

body wave, faster, travels through solids and fluids

motion is longitudinal (same direction as propagation, like a slinky)

Question 4

propogation of seismic activity

S - wave

Answer 4

surface / shear wave, slower, only travels through solids

motion is transverse (perpendicular to the direction of propogation)

Question 5

effect of rock density on seismic wave velocity

Answer 5

waves travel slower in lower densities, and faster in higher densities

Question 6

seismic discontinuity

Answer 6

abrupt changes in seismic wave activity

these changes are how we know there are layers

changes not linear - depends on the rock

Question 7

how does wave velocity change with depth

Answer 7

velocity increases with depth as there is an increase in pressure thus an increase in density

Question 8

how thick is the crust

Answer 8

oceanic crust is ~5-7km, continental crust is ~25-30lm

>1% of Eath by volume

Question 9

hypsometric curve

Answer 9

diagram of the distribution of land surface relative to sea level

Question 10

average composition, density, and formation

continental crust

chemical layer

Answer 10

dominantly granite (felsic rock), ~2.7g/cm³, forms from magma

less dense than oceanic crust

Question 11

average composition, density, and formation

oceanic crust

chemical layer

Answer 11

dominantly basalt (mafic rock), ~2.9g/cm³,

more dense than continental crust

mafic rock: rich in Fe, Mg

Question 12

properties

the mantle

chemical layer

Answer 12

82% by volume, solid rock which behaves like a fluid sometimes

seismic velocity increases sharply at the top of the mantle

Question 13

layers

the mantle

chemical layer

Answer 13

upper mantle, transition mantle, lower mantle

Question 14

composition

upper mantle

Answer 14

peridotite (ultramafic rock) xenolith (brought to the surface within magma)

only part of the mantle we have samples of

mafic rock: rich in Fe, Mg

Question 15

behaviours at depth

the mantle

Answer 15

act like a slow convection cell (over millions of years) below a certain depth

Question 16

propertes

the core

chemical layer

Answer 16

~17% of Earth by volume, primarily nickle and iron

Question 17

formation

Earth’s magnetic field

Answer 17

generated by the liquid outer core flowing due to convection around the solid inner core (flow is helical due to Earth’s rotation)

Question 18

importance to humans

Earth’s magnetic field

Answer 18

shields us from high energy radiation from the sun, as well as other cosmic rays, also used for navigation

Question 19

mechanical layers

layers based on behaviour / response to forces

Answer 19

lithosphere, asthenosphere, mesosphere, inner and outer core

Question 20

lithosphere

mechanical layer

Answer 20

outermost rigid layer composed of the crust and upper mantle, broken into plates

thicker under the continents, thinnest around mid ocean ridges

Question 21

asthenosphere

mechanical layer

Answer 21

the ductile layer which convects under the lithosphere, part of the mantle

convection currents due to heat from Earth’s core

Question 22

mesosphere

mechanical layer

Answer 22

rigid, immobile lower mantle, below asthenosphere

does not convect, subject high pressure and temp

Question 23

transition zone

of the mantle

Answer 23

inbetween the asthenosphere and the mesophere where mineral changes occur due to extreme conditions

identified by changes in seismic velocity

Question 24

outer core

mechanical layer

Answer 24

only entirely liquid layer, convects, generates magnetic field

heat escapes the lower outer core, which causes it to solidify into inne

Question 25

inner core

mechanical layer

Answer 25

innermost layer, solid due to immense pressure