L7: The Lithosphere
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who wrote the work entitled: The Origins of Continents and Oceans (1915)
Alfred Wegener
what did Alfred Wegner discover during his research?
looked at the fossil content of rocks across South America and Africa and realised the fossils were consistent across both continents. Also realised the edges of the continents seemed to fit together
what did Alfred Wegener propose?
that there had once been a supercontinent where all continental fragments had joined
what was the name given to Wegener’s supercontinent?
Pangea
what were Wegener’s proposals incorporated into?
plate tectonic theory
why were Wegener’s ideas rejected by the geological community at the time of his discoveries?
because there was no known mechanism that was thought conceivable that could move continents around the surface of the Earth
why were there many technological developments following the 2nd word war that helped shape tectonic theory? give an example
arose as by-products of weapons development anti submarine warfare (ASDIC)
how did anti submarine warfare help Harry Hess?
compiled the data that indicated whether a submarine was nearby and realised returns from the seabed gave a map of the geomorphology of the sea bed
what was ASDIC?
the method for assessing, from a surface ship, whether there was a submarine in the water nearby
what did Harry Hess detect using anti submarine warfare technology?
huge ridges that run along the bottom of the ocean and associated nearby high points
who did Harry Hess join forces with? and what did they create?
Marie Tharp a map of global geomorphology
what did Fred Vine and Drummond Mathews research (1963)?
paleomagnetic reversals in the deep ocean
what are paleomagnetic reversals?
Earth’s magnetic field has polarity (north and south pole) which periodically through geological rime reverse
are paleomagnetic reversals consistent?
yes
what did Vine and Matthews do>
looked at the geomagnetic polarity of oceanic basalt which when molten contain magnetic minerals, and that before becoming solid align
how does the geomagnetic polarity of oceanic basalt indicate paleomagnetic reversals?
because the orientation of the magnetic minerals is consistent with the prevailing magnetic field at the time
what did Vine and Matthews discover?
that the rocks adjacent to the ridges in the middle of the Atlantic Ocean have polarity consistent with present day but if you extend out from the ridge it suddenly reverses
how did Vine and Matthews discover sea floor spreading?
interpreted that magma is coming up and pushing the crust apart
how can the rate of sea floor spreading be detected?
by the distance of the polarity reversal from the spreading centre
how were Vine and Matthews able to determine the age of the lithosphere from their studies?
by looking at polarity reversals which indicate that as you move further from the ridges, the crust gets older
where is the oldest oceanic crust we have present? and when does it date to?
the Western Pacific the Jurassic
what impact is sea floor spreading having on continents?
it is pushing them apart
what role did Dan McKenzie play? (1967)
created the theory of plate tectonics by integrating sea floor spreading and continental drift
at what margins does sea floor spreading occur?
constructive plate margins in the centre of oceanic basins