Theory and Evidence Flashcards
the theory was first developed in.. and by who?
In 1620 by Francis Bacon
Who and when published his theory of continental fit?
Alfred Wegner in 1912
What did Alfred Wegner’s theory state?
All the continents were once joined together as a large supercontinent called Pangea.
Pangea split up to form…
Laurasia and Gondwana Land, which later split up to form our current continents.
Wegner collated evidence from…
Biology, geology and climatology.
Evidence from biology showed that..
- the fossils of the reptile Mesosaurus was found in South Africa and South American sediments of the Permian Age.
- plant remains from humid swamps that later formed coal has been found in India and Antarctica.
Geological evidence showed that…
- rocks of similar age, type and formation have been found in in South - East Brazil and South Africa.
- rock striations showing the same orientation are found in Brazil and West Africa.
In climatology, evidence shows…
coal deposits formed in humid tropical conditions have been found beneath Antarctic ice cap, North America and U.K.
Later in 1948, Maurice Ewing discovered what?
Mid-Atlantic ridge, continuous mountain range, during survey of Atlantic Ocean floor
Ewing noted that the rocks were…
volcanic and recent in origin, not ancient
In the 1950s…
Magnetic surveys showed regular patterns of paleomagnetic stripping around the mid-ocean ridges.
The stripes form when…
basaltic lava erupts on the ocean floor and cools.
it contains iron-rich minerals which align to earth’s magnetic field as the lava cools down.
How often does the Earth’s polarity change?
Every 400,000 years. From North to South.
The reversal of polarity shows…
bands of stripes of normal and reverse polarity rocks.
mirrored on either side of the mid-ocean ridge.
What does the mirror pattern suggest?
That new rocks are added equally on either side of the mid ocean ridge.
In 1962, what was discovered and by who?
Sea floor spreading was discovered by the scientist Hess.
this was supported by establishing the age of the volcanic rocks.
Hess confirmed that..
Newest rocks were in the centre and oldest rocks were nearer the USA continental edge
Deep ocean trenches showed that…
parts of the ocean floor was being destroyed as a result of subduction. This provided the mechanism for sea floor spreading.
Heat in the Earth’s core is produced by
Radioactive decay of uranium and radium to release heat.
Continental crust is…
- 30-60 km thick
- Very old, up to 1500 million years
- lighter, up to 2.6 g/cm3
- lighter in colour and contains Sial
Oceanic crust is…
- 6-10 km thick
- Very young, up to 200 million years
- Heavier, up to 3.0 g/cm3
- Darker in colour and contains Sima
Sea floor spreading occurs when…
New rock formed at the mid-ocean ridge pushes the old rock further away
subduction occurs where it is destroyed
