Direct evidence for the structure of the earth

Question 1

What are direct methods?

Answer 1

Actual physical evidence

Question 2

Name five forms of direct evidence for the earth structure

Answer 2

Rock samples
Drilling holes and mining
Ophiolites
Samples brought up by volcanoes
Kimberlite diamond pipes

Question 3

Describe the evidence of rock samples

Answer 3

Rock samples found in field brought to surface by earth movements and erosion
Usually from only 2-3 km below surface

Question 4

Describe the evidence for drilling holes and mining

Answer 4

Deepest hole is 13km deep the USSR
Deepest gold mine in South Africa is 4km
Samples of rocks and microfossils can be brought up on drill bits

Question 5

Describe the evidence of ophiolites

e.g. thickness, composition

Answer 5

Slabs of oceanic crust that have broken off and turned on side.
Made of sediment, basalt pillow lava, dolerite, gabbro and peridotite- complete cross section ocean crust
Up to 7km thick.
Allow us to look at layers of oceanic crust without any expensive drilling

Question 6

Describe the evidence for samples brought up by volcanoes

Answer 6

Volcanoes bring up magma from lower crust and upper mantle e.g. Basalt lavas from the MOR are formed from partial melting of the upper mantle, this can be chemically analysed to estimate the layers composition

Question 7

Describe the evidence form Kimberlite diamond pipes

Answer 7

Bring up mantle Xenoliths of peridotite and diamonds Formed under extreme pressure
Depths as much as 250km
Provides evidence upper mantle made of peridotite

Question 8

What is the ophicleide sequence?

Answer 8

Bottom
Peridotite
Gabbro
Dolerite
Basalt