1a Evidence For Continental Drift And Plate Tectonics

Question 1

Mohorovičić discontinuity

Answer 1

Boundary between earths crust and the mantle

Question 2

Lithosphere

Answer 2

Crust and upper mantle

Question 3

How hot is the core

Answer 3

6500 degree

Question 4

How hot is the mantle

Answer 4

1600 degrees

Question 5

Density of oceanic plate

Answer 5

3gcm-3

Question 6

Density of continental crust

Answer 6

2.7gcm-3

Question 7

Jigsaw fit

Answer 7

Similarity in coastline of eastern SouthAmerica and West Africa.
Best matched 1,000 meters below sea level
Some disparities due to erosion and deposition since continental separation; eustatic and isostatic change

Question 8

Geological fit

Answer 8

Eastern South America and West Africa have an ancient craton (2 billion years old) which continues from one content to another

Question 9

Tectonic fit

Answer 9

Fragment of fold mountains (450 and 400 million years ago) are found on widely separated continents today
Sections of Caledonian fold mountain belt found n Ireland, Canada, Great Britain and Scandinavia . When re assembled the belt form a continuous linear feature

Question 10

Glacial deposits and striations

Answer 10

Glacial deposit fund in Antarctica, Africa, South America, India and Australia from 300 millions years ago.
Suggesting an ice sheet covered these areas uniformly
Glacial striations (scratches on bedrock from glacier movements) show direction of ice flow from a single point

Question 11

Fossil evidence

Answer 11

Mesosaurus remains on South Africa and EASTern South America.
Glossopteris (plant) found in Southern India, South America, Africa, Antarctica and Australia showing they were once joined

Question 12

Sonar

Answer 12

Echo sounding bathymetry to map ocean floor
Discovered mid ocean ridges raised 1.5km above abyssal plain.
Found deepest parts ocean are close to continental margins
Provided evidence for sea floor spreading due to ridge push

Question 13

Paleomagnetism

Answer 13

As sea floor spreads there are bands of normal polarity and reversed polarity. The symmetry and age of the rock also helped prove spreading from a single point
Sea floor spreading as part of plate tectonic theory

Question 14

Seismic profiling

Answer 14

Provided detail about sea bed composition: only oceanic rock, not continental
Thicker sediment further from the mid ocean ridge shows it has more time to accumulate so this rock is older.

Question 15

sediment cores

Answer 15

from ocean drilling programme
use carbon dating and dredging
rocks further from mid ocean ridge had more sediment and were older
dredged rocks from ocean floor included only basalt, gabbro and serpentinite - no continental materials

Question 16

GPS

Answer 16

shows continents moving apart e.g Australia has been moving about 2.7 inches per year.
different speed of each plates and their movement shows tectonic plates glide over the mantle in a seperate layer.

Question 17

seismic tomography

Answer 17

proves slab pull
uses thermal imaging to show difference between cold subducted plates and depict trenches and plate melting
uses refraction of S and P waves to show layers of earth