Plate Movement Flashcards
Describe the core of the earth
Size of Mars Densest part of the planet Rocks rich in nickel and iron Two parts : semi molten outer core and a solid inner core Temperature 5000c
Describe the mantle of the earth
Surrounds core Mainly silicate rocks rich in iron and magnesium Most is semi molten Up to 3800c Densities increase as you go down mantle
Describe the crust of the earth
Thinnest layer, coolest, less dense rock
Rich in silicon, oxygen, aliminium, potassium and sodium
What are the two types of crust
Oceanic crust
Continental crust
What’s oceanic crust
Thin layer, younger basalt rock known as sima ( Silica and magnesium)
Thickness - 5-10km
What’s continental crust
Thicker layer of older, lighter granite rocks (sial ( silica and aluminium) crust up to 70km thick
What’s Alfred wegeners theory (1912)
All continents were once joined in ancient supercontinent Pangea. At some point the land masses had drifted apart until they occupied their current position
Evidence for wegeners theory of continental drift
- continental or jigsaw fit
- geological evidence
-climatological evidence
Biological evidence
What is the continental or jigsaw fit evidence
Some continents seem to fit together if placed beside each other eg Africa and South America
What’s the geological evidence for wegeners theory
Rocks of the same age and type and formation found in SE Brazil and South Africa
Similar glacial deposits found in Antarctica and South America and India ( thousands of km apart )
What’s the climatological evidence for wegeners theory
Places as far apart as Antarctica,North America and the U.K. contain coal deposits of a similar age that were formed in tropical conditions. They are no longer in tropical conditions so must have drifted apart
What’s the biological evidence for wegeners theory
Similar fossil formations are found either side of the Atlantic.
Plant remains from humid swamps that later formed coal deposits have been found in India and Antarctica
What did Harry Hess do ( sea floor spreading)
Updated wegeners ideas. Examined crust either side of mid Atlantic ridge
Studied age of rocks on Atlantic Ocean floor he found the youngest in the middle and oldest nearest USA. New rocks still been formed in Iceland
Evidence for sea floor spreading
Look at crust either side of mid Atlantic ridge
Palaeomagnatism
What is palaeomagnatism - evidence of sea floor spreading
Study of changes in earths magnetic field (polarity. Earths magnetic field switches polarity.iron records record magnetic field. Rocks in ocean crust show alternating polarity.,magnetic stripes are mirrored across ridge suggest ocean crust spreading
What are convection currents
Slow moving thermal currents Hotspots heat lower mantle creating thermal currents rise and sink. This circulation of magma allows plates to move.
Sea floor spreading means more crust is created so earth would get bigger? But it didn’t, why??
Parts of earths crust were being destroyed. On Pacific coast submarines found deep ocean trenches which were destroying crust as new crust was created. It did this by subduction and provided mechanism for drifting of continents
Why are oceanic plates younger than continental
They are denser so can sink therefore are destroyed at ocean trenches and are continuously being formed at ocean ridges.
Continental plates won’t sink due to low density
What is a constructive plate margin
Where two sections of crust move apart
Can be two sections of oceanic crust
Or oceanic and continental crust
Process that happens at constructive margin with two oceanic plates
Crust weakens and cracks and magma pushed through gaps it cools and solidifies and forms submarine volcanoes. The pulling apart can form faults
Process that occurs at constructive margin between oceanic and continental crust
Only occurs where there’s a convection cell . Continental crust heated by cell.over time crust cracks (vertical faults) and moves apart
Landforms that happen in oceanic areas where plates move apart
Mid Oceanic ridges eg mid Atlantic ridge overall they have a total length of 60,000km on planet.
Transform faults cut along ridge,Middle of ridge forms deep valley
Underwater volcanoes erupt along mid ocean ridges.
Landforms that can happen at constructive plate margins when oceanic and continental plates drift
Rift Valleys. Formed when lithosphere stretches causing it to fracture into sets of parallel faults.land between faults then collapses into deep wide value eg great African Rift Valley extends 4000km from Mozambique to Red Sea. Magma rise though gaps-volcano
What happens at a destructive margin,what types are there
Two sections of crust move towards each other, can be:
- oceanic -continental
- continental -continental
- oceanic -oceanic
