Plate Tectonic Theory Of Crustal Evolution Flashcards
What did Alfred Wegener publish in 1912
A theory suggesting that all the continents were once joined together in an ancient supercontinent called Pangea
What evidence was there for Wegeners theory
Continental fit
Geological evidence
Climatological evidence
Biological evidence
What is meant by continental fit
Some continents seem to fit together if placed beside each other(Africa and South America)
What geological evidence is there for Wegeners theory
Rocks of the same age and type and displaying the same formations are found in SE Brazil and South Africa
Trends of mountains in eastern USA and NW Europe are similar when they are placed in their old positions
What climatological evidence is there for Wegeners theory
Places as far apart as Antarctica, North America, Svalbard and the UK all contain coal deposits of similar age that were formed in tropical conditions. Must have drifted apart since Carboniferous period
What biological evidence is there for Wegeners theory
Similar fossil formations are found on either side of the Atlantic.
Plant remains from humid swamps that later formed coal deposits have been found in India and Antarctica
When did additional discoveries about Wegeners theory take place
1940s onwards
What did an examination of he ocean crust either side of the mid Atlantic ridge suggest
Sea floor spreading was occurring
What evidence was there that the sea floor was spreading
Alternating polarity of the rocks that form the ocean crust.
Iron particles in lava erupted on the ocean floor are aligned with the earths magnetic field.
Rocks are aligned alternatively towards north and south poles
Other supporting evidence of sea floor spreading
Age of ocean floor. Older crust is continually being pushed aside by newer crust
Where did surveys record very young ages for places (example of a young place)
On or near the mid oceanic ridge e.g. Iceland
Where are older ages for ocean floor rocks found
Near the continental masses (200 million years).
What issue was raised with sea floor spreading and how is it incorrect
It implies that the earth must be getting bigger.
Huge oceanic trenches were found where large areas of ocean floor were being pulled downwards such as around the fringes of the Pacific Ocean
What provides the mechanism for sea floor spreading and the drifting of the continents
Subduction
Why is continental crust geologically more complex and contains older rocks
Landmasses are being moved around by movements of the ocean crust being changed by the addition of newer rocks, and folded and faulted by collision and subduction
