Plate tectonic theory Flashcards
What was Bacon’s theory (1620)?
He hypothesised that parts of the world could fit together like jigsaw pieces: the West coast of Africa and the East coast of South America could possibly fit together.
What are the weaknesses of Bacon’s theory?
No evidence available to support the theory.
What was Wegener’s theory?
He hypothesised that a single continent existed 300 million years ago (Pangaea): this continent was split into Gondwanaland (southern continent) and Laurasia (northern continent).
How can any gaps or overlaps which undermine Wegener’s theory be explained?
- coastal erosion
- coastal deposition
- changes in sea level (eustatic change)
- changes in land level (isostatic change)
What climatological evidence can be used to justify Wegener’s theory (continental drift)?
Evidence of past glaciation (24 million years ago) can be found in tillites (deposits) which are located in South America, Antartica and India.
What biological evidence can be used to justify Wegener’s theory (continental drift)?
Fossil remians of the reptile the Mesosaurus are found in both South America and southern Africa.
What geological evidence can be used to justify Wegener’s theory (continental drift)?
Rocks of the same age and type (e.g cratons) are found where Scotland and Northern Canada would have fit together.
What tectonic fit evidence can be used to justify Wegener’s theory (continental drift)?
The Caledonian Belt (a belt of uplift) can be seen across different continents in areas such as Scotland, Ireland and New Foundland.
What was Holmes theory?
He hypothesised the earth’s internal radioactive heat is the driving force of mantle convection (convection currents) which moves tectonic plates. He also believed there were two different types of crustal plates (sial and sima)..
What was the theory created by Tharpe, Ewing and Heezen (1950s-1960s)?
They hypothesised that the mid-oceanic ridge was caused by sea-floor spreading:
- Hezeen collected data relating to the sea floor using sonar.
- Tharp used the data to map a huge valley in the middle of the ocean ridge in the North Atlantic. She therefore discovered the Mid-oceanic Ridge.
What was Hess’s theory (1962)?
He hypothesised that the mid-oceanic ridge, in the middle of the Atlantic, were formed due to the cooling of magma into new rock at a constructive plate boundary.
What is a mid-ocean ridge?
An underwater mountain range, formed by tectonic movement (constructive plate boundary).
What evidence supports Hess’s theory (1962)?
New rock can be found in Iceland which is found towards the middle of the oceanic ridge whereas the oldest rock can be found in America, towards the edge of the mid-oceanic ridge.
What was Vine and Matthew’s theory (1962-63)? What did their investigation show?
1.They hypothesised that paleomagnetism (changes in the earth’s polarity) can be used as evidence for sea floor spreading.
2. the earth’s polarity (magnetism) changes every 400,000 years and new rock settles evenly on either side of the oceanic ridge which is arranged in a symmetrical pattern of magnetic stripes (at equal distances) along the sea floor.
What is the main weakness of Hess’s theory?
He could not explain how the ocean floor was being destroyed and recycled since sea-floor spreading implies that the world is expanding.
