Plate Tectonics Flashcards
Provide evidence proving continental drift
Glossopteris fossils remains in similar rock layers all formed in Antarctica, Australia, South America, Africa and India which lived in wet swampy regions
Mesosaurus remains being found in South America and Africa even though freshwater lakes and ponds don’t exist in Africa
Scratches from glaciers found in central tropical Africa…
Fossils of palm trees found in frozen Alaska
What did Abraham Ortelius say was the cause of the movement of today’s countries position?
Continental Mutations
How was the continental mutations the reason of the placement of the continents?
Abraham Ortelius … suggested that the Americas were “torn away from Europe and Africa … by earthquakes and floods” and went on to say: “The vestiges of the rupture reveal themselves, if someone brings forward a map of the world and considers carefully the coasts of the three [continents]”
What did Dwight Dana say was the cause of the movement of today’s countries position?
Permanence Theory
What did Charles Darwin say was the cause of the movement of today’s countries position?
The Earth expanding
What did Alfred Wegener say was the cause of the movement of today’s countries position?
Continental drift
What did he think was the cause of continental drift?
The mechanisms causing the drift might be the centrifugal force of the Earth’s rotation or the astronomical precession.
What did Arthur Holmes propose the mechanism for continental drift was?
“Convection currents” in the liquid rock underground move the solid rock on the surface.
Why wasn’t the convection currents idea accepted?
It gave continental drift a mechanism, but he couldn’t find any new evidence for his new idea, so geologists weren’t too keen on it.
Provide examples of evidence for the convection currents
Ocean-floor spreading (and the mid-ocean ridge)
Magnetic evidence in sea-floor rocks
The age of the sea-floor spreading zones
The location of earthquakes (and volcanos)
Direct measurement (needed to wait for accurate GPS)
How does magnetic evidence in sea floor rocks prove the tectonic theory?
Earth is a giant magnet, with a magnetic field that surrounds it. When lava cools, bits of ‘moving’ iron lock in place, keeping track of which way the magnetic pole was at that time. (like compasses freezing in place)
Every few million years Earth’s magnetic field switches direction. The end result is magnetic ‘stripes’ of alternating directions being created on the ocean floor.
Therefore magnetic striping on the ocean floor provides evidence that the sea floor is spreading away from the mid-ocean ridges and explains how the continents move.
How does the age of the sea-floor spreading zones
prove the tectonic theory?
By drilling they have found that rocks near the ridge are youngest, and they get older as you get further away.
This is just what plate tectonics theory would predict
Examples of continental movement
Arctic Ridge expanding by 2.5 cm per year
East Pacific rise, off the coast of Chile 15 cm/year
Current movement tracked by satellites and GPS
Australia about 2cm / yr north (about as fast as your fingernails grow)
Define subduction
The action or process in plate tectonics of the edge of one crustal plate descending below the edge of another.
Describe transform boundaries
Sliding past each other Produces earthquakes (more shallow) but often nothing much visible on the surface
