Evidence for plate tectonic theory

Question 1

What was the VERY first theory about plate tectonics?

Answer 1

Francis Bacon.

West coast of Africa and Europe seem to have a “jigsaw fit” with the Eastern seaboard of North and South America.

Question 2

What was the ‘breakthrough’ on plate tectonic theory?

Answer 2

Alfred Wegener.
One supercontinent (Pangea) - 300 million years ago - slowly drifted apart.
Laurasia - north.
Gondwanaland - south.
Present continents formed from further splitting of the two masses.

Question 3

What is some geological evidence that supports Wegener’s theory? 4

Answer 3

1. Fit of South America and Africa.
2. Carboniferous glaciation evidence (290 million years ago).
   Deposits found in South America, Antarctica and India.
   Unexplainable by their present position.
3. Rock sequences in northern Scotland and eastern Canada - laid down under the same conditions in one location.
4. Appalachian Mountains chain - goes from northeastern U.S. to Ireland, GB and Greenland, despite the Atlantic Ocean being in the way.

Question 4

What is paleomagnetism and how does it support Wegener’s theory?

Answer 4

Mountain ridge discovery - Mid Atlantic Ridge.
Vine/Matthews discovered magnetic stripes running parallel to the ridge - 1960s.
Stripes corresponded to times when Earth’s magnetic field reversed from North to South.
Iron particles in the erupting magma - cooled and aligned themselves with the Earth’s polarity at that time.
Magnetism - switches 4/5 times in 10 million years.
Supports Hess’ sea floor theory.
Furthest away are oldest - 156 million years old.
Newest rocks - only 10 million years old.

Question 5

What is some biological evidence that supports Wegener’s theory? 4

Answer 5

1. Fossil brachiopods in Indian limestones - similar fossils in Australia.
2. Reptile Mesosaurus fossil remains - found in both South America and southern Africa.
3. Plant fossil remains which existed when coal was being formed - only been located in India and Antarctica.
4. Reptile Chirotherium Fossil footprints in the Isle of Arran - matched in Eastern Canada.
   Suggesting the North American and European continents used to be joined.