Lecture 2 - The Deep Flashcards
What did he suggest about the continents of the Earth?
That a very long time ago all land had been joined together in one huge continent called Pangea
Alfred Wegner (1880-1930) used what as an analogue for how continents could float
Icebergs
What evidence did Wegner use to support his theory?
Faunal and floral evidence
What 4 examples of faunal and floral evidence was there to support Wegners theory?
Mesosaurus
Glossoptreus
Lystrosaurus
Cynognathus
What other evidence did Wegner have?
- The continents appeared to match up
- Distribution of fossils across southern continents suggested prior connectivity
What did Dr. Chamberlin, University of Chi-Town wassup, comment on Wegners theory?
‘Wegners hypothesis takes considerable liberty with our globe, and is less…tied down by awkward ugly facts than most of its rival theories.’
During the Cold War (1945-1989) oceans became a battlefield, so what was needed?
Accurate underwater charts
The echo sounder resulted from anti-submarine warfare, what did the short and long delay mean?
Short Delay = shallower depth
Long delay = greater depth
What was revealed by echo-sounding across the Pacific Ocean?
A rugged sea floor topography
Seismic surveys showed more than just the sea floor, by penetrating the ocean floor what other geological layers were revealed?
- Sediment (1km)
- Denser oceanic crust, made from basalt, an igneous rock (7km)
When was the first detailed map of ocean floor topography revealed?
1956
Measuring the strength of the magnetic field in the rocks of the sea floor showed what?
They ran parallel to ocean ridges
What is magnetite?
Motonori Matuyama realised iron rich rocks can be magnetised, but magnetism differs from place to place
Where else do magnetic fields emanate?
The surface of the sun, and the aurora borealis
What doe the Earths magnetic field shield is from?
A stream of ionised gases (the solar wind) that blows outwards from the sun at 400km/second
Harry Hess (1906-1969) after WWII speculated the origin of the ocean floor. Why is the ocean floor lower than continents?
- density of basalt 3.3x density of water
- continents average about 2.8x the density of water
Hess coined the phrase sea floor spreading, what is it?
When basaltic lava erupts on the sea floor, builds mountains along the mid ocean ridge, they then appear to move away over time. Also where basalt came in contact with sea water it became serpentine
Prof. Fred Vine researched ocean floors and magnetic anomalies, what did he conclude?
Rocks on ocean floor were volcanic basalts, erupted from the mantle and there was a clear relationship between patterns of magnetic anomalies, ocean ridges and eruption of basalt
Magma erupts, cooled and magnetised and then carried away by sea floor spreading. What happens when the Earths magnetic field switches?
New ocean floor erupts, cools but has reverse magnetisation
Name 3 things drilling of the ocean floor discovered?
- Symmetrical patterns of magnetic anomalies
- New ocean crust added at a rate of 3.5km yr
- Most of ocean crust younger than 200 million years old
When did Europe and Africa begin to rift from America pulling Pangea apart?
During the Jurassic Period, (200-150 Ma) as sea level began to rise
What developed across Britain and the North Sea?
Tectonic rift basins which were filled with warm shallow seas
When did rifting reach it’s maximum in the North Sea?
150 milli years ago
What did extensional tectonics across the North Sea produce?
A deepening basin, which trapped sediment. The sediment then compressed into shale, a type of rock
What was rapidly deposted?
Marine mudstones, rich in organic matter, accumulated through rift basins, with deposits exceeding 3000m
Upper Jurassic (165-150Ma) marine shales are important for what?
Petroleum source rock worldwide
Conclusion: exploration of the ocean floor has bought together who changing the way we view the planet?
Oceanographers, geologists, biologists
Conclusion: Ocean floor shown to be one of the most dynamic places on Earth, what does it affect?
The environment we live in
Conclusion: What is still being made?
New discoveries
