theories

Question 1

what is continental drift theory?

Answer 1

the theory that continents move through oceans

Question 2

evidence to support continental drift theory?

Answer 2

1. fossil evidence did not match: fossil remains of the same species were found on two different continents eg fossils of the same green plant have been found in all continents indicating that once all the climates were the same.
2. glacial evidence did not match: but when the countries are re-arranged to Wegners theory, the glacial flow fits with our understanding of how glaciers move.
3. rocks of the same type found in different continents: when using his theory, these rock types fit together to form one long mountain range.

Question 3

why was Wegners theory on continental drift discarded?

Answer 3

though he gave evidence to support his theory, he could not explain WHY- what caused the plates to move and therefore was discounted by most scientists.

Question 4

what is the theory of plate tectonics?

Answer 4

the theory that all of the earths surface is made up of tectonic plates that move, causing major geological events along the boundaries between them.
this is driven by:
-mantle convection
-slab pull
-subduction
-sea floor spreading

Question 5

what is sea floor spreading?

Answer 5

molten rock up up from earths interior along mid ocean ridges creating new seafloor that spreads away from the active ridge.

evidence to support:
1. age of rock found increases as you move further away from ridge
2. paleomagnestism

Question 6

what is paleomagnetism?

Answer 6

it is the study of magnetic alignments of rock at divergent plate margins.

swirling in the outer core creates magnetic field. every few 400,000 years the magnetic field of earth flips causing the magnetic north and south poles to swap. when lava cools becoming rock: minerals inside line up with earths magnetic polarity (direction) at the time.

the changes of polarity in the rock (the study of paleomagnetism) supports sea floor spreading: scientists found same pattern of magnetic direction either side of the ridges- only possible if new rock is being formed at the same time on both sides.

Question 7

what is slab pull?

Answer 7

when the newly formed oceanic crust sinks into the mantle, pulling the rest of the plate down with it. reason for 80% of earths tectonic movements is due to this pull.

Question 8

what is mantle convection?

Answer 8

the heat produced by radioactive elements in the earths core rises heating the mantle. this creates convection currents. these hot liquid magma currents operate as cells (convection cell) however the imoortance of this contributing to plate movement is disputed. it is likley to be a combined force of convenction and gravity driving tectonic plate movement (slab pull/ subduction)