Physical- Plate Tectonics Flashcards
What is the asthenosphere?
Semi-molten part of the mantle.
How thick can Continental crust reach up to?
30-70km deep. Continental crust is less dense that oceanic crust.
Why do tectonic plates move?
Radioactive decay in the core causes heat emissions. The lower parts of the mantle heat up- becoming less dense- and rise. When they reach the top they cool- becoming denser- and sink downwards.
What idea did Alfred wenger propose the idea of?
Continental drift.
What did Alfred wenger base his theory on?
Geological evidence and fossil records- however he could back up his theory with solid evidence so people dismissed it.
What is paleomagnetism?
It is the study of the history of the earths magnetic field.
How has palaeomagnetism provided evidence of continental drift?
It has provided evidence for sea floor spreading- when magma erupts,it aligns itself with the direction of the magnetic field. Every 200,000 years, the earths magnetic field reverses its polarity- creating a series of magnetic stripes in the crust-older stripes are pushed further away.
What is a constructive margin?
Where the plates move apart.
What two landforms are created at a constructive margin?
1) mid-ocean ridge- where two oceanic plates move apart as magma rises from the mantle. Underwater volcanoes are formed.
2) Rift Valley- where plates move apart and land in the middle sinks.
Give one example of a destructive plate margin.
Eurasian and Pacific plate (coast of Japan)
What are intrusive features?
Volcanic activity that occurs beneath the earths surface.
Give 3 intrusive feature.
Batholiths, dykes, sills.
What are dykes?
Vertical intrusions in underlying rock. Magma rises but cools in horizontal cracks before it reaches the surface- they occur across layers of rock.
How are sills formed?
Magma cools in horizontal intrusions and creates vertical cooling cracks. They occur between layers of rock.
What is the lithosphere?
The rigid part of the mantle and the crust.
