Plate Tectonics- Key Terms

Question 1

What is the continental shelf?

Answer 1

The part of continental crust that extends into the sea past the land masses and forms a shelf like feature

Question 2

What is tectonics?

Answer 2

The theory that tries to explain how the Earth is structured and what it is made up of

Question 3

What is the crust?

Answer 3

The thinnest, top layer of the Earth made of the coolest, less dense rocks

Question 4

What is the Big Bang?

Answer 4

The explosion of a star which threw out aggregation of materials which formed Earth

Question 5

What is the mantle?

Answer 5

The mantle is from the bottom of the crust down to around 2900km. It surrounds the core and is mainly silicate rocks rich in iron and magnesium.

Question 6

What is the core?

Answer 6

The core is at the centre of the Earth and made up of rocks rich in iron and nickel. There is a semi molten outer core and a solid inner core.

Question 7

What is the lithosphere?

Answer 7

The lithosphere consists of the crust and rigid upper mantle. It is the zone where tectonic plates are formed.

Question 8

What is the asthenosphere?

Answer 8

The asthenosphere consists of the semi molten part of the Earth’s mantle

Question 9

What is Moho discontinuity?

Answer 9

The asthenosphere is 10% molten material so when seismic waves travel through it, they slow down and this is called Moho discontinuity.

Question 10

What are primary (P) waves?

Answer 10

Primary (P) waves are the fastest seismic waves that arrive first and can travel through both liquids and solids. They are compressional waves so they vibrate in the same direction as they are travelling.

Question 11

What are secondary (S) waves?

Answer 11

Secondary (S) waves travel at half the speed of P waves. They shake the ground from side to side and vibrate at right angles to the direction of travel.

Question 12

What are surface (S) waves?

Answer 12

Surface (S) waves are unable to travel through liquids and are restricted to the Earth’s surface. They are much slower than secondary waves.

Question 13

What are tectonic plates?

Answer 13

Tectonic plates are irregularly shaped rafts of lithosphere floating on the plastic asthenosphere underneath

Question 14

What is continental crust?

Answer 14

Continental crust is usually over 1500 million years old. It is permanent and can extend beyond the margins of current land masses. It will not sink because of its’ lower density.

Question 15

What is oceanic crust?

Answer 15

Oceanic crust is less than 200 million years old. It is much denser than continental crust and is continually being formed and destroyed at plate margins.

Question 16

What are plate margins?

Answer 16

Plate margins are where two plates meet and either move towards eachother, away from eachother or past eachother.

Question 17

What are convection currents?

Answer 17

Convection currents are circular movements of heat within the asthenosphere (upper mantle) which drive the movement of plates

Question 18

What is continental drift?

Answer 18

Continental drift is the theory that originally all continents were joined together as a land mass called Pangaea and have drifted apart over time.

Question 19

Who was Alfred Wegener?

Answer 19

Alfred Wegener was the first person to publish the theory of continental drift in 1912

Question 20

What is meant by jigsaw fit?

Answer 20

Jigsaw fit is the fact that some continents appear to fit together like jigsaw pieces if they were put next to eachother e.g. Africa and South America

Question 21

What is Pangaea?

Answer 21

Pangaea is an ancient supercontinent which originally joined together all the continents. It forms part of Wegener’s theory of continental drift.

Question 22

What was a glossopteris?

Answer 22

Glossopteris is a fern that has been found in Africa, Antarctica, Australia and South America. It suggests that these continents were all once linked and had a similar climate.

Question 23

What is a mesosaurus?

Answer 23

Mesosaurus is an extinct reptile that has been found in Africa and South America. It was a costal animal which could not have crossed the Atlantic Ocean- this suggests that these continents were once linked.

Question 24

What is sea floor spreading?

Answer 24

Sea floor spreading is the theory that the Atlantic sea floor is spreading out from the centre at the speed of about 5cm per year

Question 25

What is the Mid Atlantic ridge?

Answer 25

The Mid Atlantic Ridge is a ridge of mountains running along the middle of the Atlantic Ocean from which the sea floor appears to be spreading outwards.

Question 26

What is paleomagnetism?

Answer 26

Paleomagnetism is the switching of the Earth’s magnetic field every 400,000 years which causes North and South to swap around, creating a pattern of magnetic stripes in rocks, which supports the theory of sea floor spreading.

Question 27

Who were Vine and Matthews?

Answer 27

Vine and Matthews (1960s) were British geologists who discovered magnetic stripes running parallel to the Mid Atlantic ridge.

Question 28

Who was Harry Hess?

Answer 28

Harry Hess (1962) was an American geologist who updated Wegener’s ideas by studying the age of rocks beneath the Atlantic. He found out that younger rocks were in the middle next to the ridge whereas older rocks (around 200 million years old) are further out from the centre which supports the idea of sea floor spreading