Plate Tectonic Theory

Question 1

what did Alfred Wegener discover?

Answer 1

all continents fit together in some way
e.g south america and africa

Question 2

when did Alfred wegener make his discovery?

Answer 2

1912

Question 3

what is continental drift?

Answer 3

continents drifted apart 300 million years ago

Question 4

what evidence was there for continental drift?

Answer 4

fossils found in indian limestone compare with
glacial deposits found in antartica, south america and africa. from late carboniferous

Question 5

what is the main issue with continental drift theory?

Answer 5

no explanaition for how this happened

Question 6

what was the evidence of continental drift theory?

Answer 6

• mid atlantic ridge, sea floor spreading (Harry Hess)
  oldest rocks near coast, newest near centre, suggests sea floor spreading.
• 1929, Arthur Holmes, convection currents, when a substance is heated its density decreases and it rises, until it cools enough and sinks again. this causes plates to move
• gravitational sliding occurs on mid atlantic ridge due to higher elevation of plates at ocean ridges. it is when fresh magma is erupted and cools as lava. next eruption pushes old lava dow. this causes the plates to move apart (ridge push

Question 7

what is plaeomagnetism?

Answer 7

iron particles in lava erupted onto sea floor are alligned with earths magnetic field. old lava provides record of earths polarity at the time of eruption.

Question 8

what is slab pull?

Answer 8

weight of cold older denser plate material sinking into the mantle at deep ocean trenches and pulling the rest of the plate with them as gravity causes them to slide downwards

Question 9

at what rate is the mid atlantic ridge dpreading?

Answer 9

5cm per year

Question 10

what are rift valleys?

Answer 10

when plates move apart on the continental areas. Lithosphere stretches leading to faults, land between the faults collapses. An area between the parralel rift valleys forms an upstanding block known as a Horst.

Question 11

what is a deep ocean trench

Answer 11

denser plate subducts, downwarping part forms a deep ocean trench
example - Mariana trench

Question 12

what is an island arc?

Answer 12

descending plate enters hotter surroundings, coupled with heat from friction, melts and rises to suface as plutons of magma. this creates complec composite volcanoes, these erupt and form islands offshore