The continents were once a single landmass surrounded by on large ocean.
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Transcript of The continents were once a single landmass surrounded by on large ocean.
![Page 1: The continents were once a single landmass surrounded by on large ocean.](https://reader030.fdocuments.us/reader030/viewer/2022032723/56649d0e5503460f949e3a92/html5/thumbnails/1.jpg)
Theory of Continental Drift
The continents were once a single landmass surrounded by on large ocean.
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Theory of Continental DriftRocks have different
density, so a less dense rock will ‘float’ on a more dense rock.
The continental shelf (part of the lithosphere) is lighter than the asthenosphere.
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Theory of Continental DriftThis process is called
buoyancy.
The lighter and heavier materials will form a balance called an ‘isostatic equilibrium’.
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Theory of Continental DriftThe continents ‘float’
on the asthenosphere like a boat floats on the ocean.
All they need is a ‘current’ to move them.
![Page 5: The continents were once a single landmass surrounded by on large ocean.](https://reader030.fdocuments.us/reader030/viewer/2022032723/56649d0e5503460f949e3a92/html5/thumbnails/5.jpg)
Theory of Continental DriftOriginally, there was
one huge continent called Pangaea.
It was surrounded by a single ocean called Panthalassa
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Theory of Continental DriftAlfred Wegener
developed his theory in 1912 based on the fossil record.
No one believed him. He was a meteorologist and couldn’t explain how it could happen
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Theory of Continental DriftIn the 40’s, new
technology revealed physical characteristics on the sea floor that showed how the continents might ‘drift.’
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Theory of Continental Drift
They revealed mid-ocean ridges, trenches and rift valleys.
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How the Sea Floor Spreads
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How the Sea Floor SpreadsHarry Hess and Robert Dietz suggested an
explanation of both how the sea floor could expand and ‘push’ the continents over the face of the Earth.
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How the Sea Floor SpreadsThe denser
(heavier) ocean crust slides under the less dense (lighter) continental crust forcing the continents further apart.
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How the Sea Floor Spreads
When the spreading seafloor reaches a continent, it is pushed below the continent in a subduction zone.
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How the Sea Floor Spreads
This brings the sea floor with it’s minerals and water below the continent.
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How the Sea Floor Spreads
Friction causes the sea floor to melt. The lighter magma flows upwards through cracks, forming volcanoes.
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The Ring of Fire
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The Ring of FireThis can be seen in
the ‘ring’ of active volcanoes surrounding the Pacific Ocean.
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The Ring of FireThese are the plates
that form these subduction zones
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The Ring of Fire