Plate tectonic theory Flashcards
Who was Alfred Wegener?
a german
What was Wegener’s theory about?
the theory was that there was a supercontinent about 300 million years ago, it slit into two continent and that today’s continents were formed from the two continents splitting up.
what is the name of the supercontinent?
Pangea
what was the name of the southern continent?
Gondwanaland
what was the name of the northern continent?
Laurasia
what did the geological evidence include?
- the fit of South America and West Africa
- deposits found in South America, Antarctica and India-evidence of late-carboniferous glaciation.
- striations in Brazil and West Africa which indicate a similar situation.
- rock sequences in Northern Scotland and Eastern Canada indicate they were laid down in the same conditions in the same place.
what does the biological evidence include?
- fossil brachiopods found in Indian limestone are comparable with similar fossils in Australia.
- fossilised remains of a plant which existed when coal was being formed have been located only in India and Antarctica.
what is the mid-Atlantic ridge?
a boundary where two lithospheric were rifting or being pulled apart
who created the theory of seafloor spreading?
Harris Hess
What did he do?
he was a US navy in WW2?
What did he use to create this theory?
Sonar (echo sounding underwater) to map the ocean floor across the North pacific.
When was the theory of seafloor spreading published?
1962
what did he discover?
oceans were shallower in the middle and identified the presence of Mid Ocean Ridges.
what did he theorise?
Oceans grew from their centres and that the crust was destroyed at the ocean trenches.
what did Vine and Matthews publish a paper about in 1963?
magnetic anomalies over ocean ridges. (paleomagnetism)
what did Vine and Matthews work look at?
magnetic strips on the ocean floor
what does the theory say about the Earth’s magnetic field?
the Earth’s magnetic field switches direction over time from its current (normal) direction to the opposite (reversed) direction
how often does the Earth’s magnetic field change?
400,000
what does material from the mantle do when it rises up through mid-ocean ridges and cools?
preserves a record of the polarity of the Earth’s magnetic field. Due to magnetites in the basalts being strongly magnetic.
what was noticed about the pattern of mid-ocean ridges?
there was a symmetrical pattern of magnetic strips
what was found once basalts (rocks) were dated?
they were found to be the same age at similar distances away from ridge on each side.
What did the symmetrical pattern suggest?
the ocean floor was created by the mid-ocean ridge
which scientists works supported Harry hess’s words?
Morley
why is palaeomagnetism possible?
minerals that make up the rock become permanently magnetised despite being parallel to the earth’s magnetic field at the time of their formation
