Download Plate Tectonics Theory. 1620 - English philosopher Francis Bacon

Plate Tectonics Theory.
1620 - English philosopher Francis Bacon wrote about the long held view that
the land on either side of the Atlantic 'fitted together' and must be related.
1912 - Alfred Wenger used 300 years of topological and geological evidence to
put forward his theory that the continents were once all joined together in an
ancient supercontinent called Pangaea. He proposed that the continents had
subsequently 'drifted' apart to their present positions. Critics pointed out that
there was no mechanism by which the continents could move over an 'obviously'
solid Earth.
Wenger’s evidence:
1. Continental Fit
Some continents (such as the western seaboard of Africa and the eastern
seaboard of South America) seem to fit together if placed side by side.
This is particularly true if the continental shelves are taken into account
as the true edges of the land masses.
2. Geological evidence
3. Climatological evidence
4. Biological evidence
Discoveries in the 20th Century:
1948 – The Mid-Atlantic Ridge
1950s – Magnetic surveys of the ocean floor
1950s and 60s – Ages of the oceans floor were measured...
BUT...
If the crust was pulling apart and being added to on the ridges, why was the
planet not getting larger?
ANSWER....
Crust must be being destroyed somewhere!
As no one could see it on the land, they looked in the sea. They discovered....
Current theory state – Convection currents: