Earth structure, plate tectonics theory: convection currents and sea-floor spreading. Evidence: continental drift and palaeomagnetism. Flashcards
How thick is the crust at oceanic plates?
5km
How thick is the crust at continental plates?
30-100km
What is the mantle?
a zone of molten silicates and other minerals
What is the Asthenosphere?
upper part of the mantle
80km deep
rocks kept in semi-molten state
What is the difference in composition between the crust and the mantle?
Asthenosphere contains more iron, magnesium and calcium than the crust
The lithosphere
cooler and more rigid than the deep mantle
Broken up into moving plate that contains worlds continents and oceans.
Thought to float on top of underlying asthenosphere.
What moves the tectonic plates
convection currents
How old are most of the continental plates?
over 1,500 million year old
What do the continental plates mostly contain?
silica, aluminium and granites
How much of the earths mass does the mantle take up?
2/3
What creates the magnetic field?
as the earth rotates, the liquid outer core spins
How deep is the outer and inner core?
Outer: 2,200km
Inner: 1,250km
How deep is the mantle?
2,900km
Why is the outer core liquid?
slightly less pressure than the inner core
Why is the inner core solid?
twice as dense as the outer core due to metallic composition rather than stoney.
Metals: 80% iron 20% nickel
What is the border between the mantle and core called?
the Gutenburg discontinuity
What causes mantle plumes?
decay of radioactive materials in the core that creates a blow torch effect up to the crust.`
Who was Alfred Wegner?
German meterologist and first to present the argument supporting continental drift.
What was wegners evidence?
the fit of the continents, glacial till deposits, shifting of climatic belts over time.
Later on paleomagnetism, convection currents and sea floor spreading added to it.
Much more steamlined galcial scarring
What was the name of the super-continent
Pangea
What was his observation about the continents in the southern hemisphere?
that they exhibit an identical pattern of rock and fossils known as the ‘Gondwana sequence’
What is Paleomagnetism?
when the hot magma rises to the arths surface and cools, the minerals themselves (magnetite especially) becomes magnetised in alignment with the Earth’s current magnetic field.
How does the earths mantle behave?
Plastically
Why does hot magma rise at oceanic ridges?
hot magma rises because it is less dense than the surrounding magma.
