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If you look at a map of the world, you may notice that some of the continents could fit together like
pieces of a puzzle…..the shapes of the coastlines of Africa and South America are a good example. As
you discovered through your modeling activity, they once fit together.
The Earth as we see it was not always like it is today. Land masses have been pulled apart and joined
together by the process we call Plate Tectonics….
Continental Drift
Alfred Wegener proposed
in 1910 that 250 - 300
million years ago all
continents were joined
together in a single land
mass that drifted apart.
Fossils of the same plants
and animals were found
on different continents.
Wegener called this
supercontinent Pangaea,
Greek for “all Earth or all
Evidence of Continental Drift
Fit of
Across the
Evidence of Continental Drift
Evidence of Continental Drift
Similar rock layers along the edges and relationship among mountain ranges on different continents
Red line marks area where start of separation between Africa and South America
probably started
Sea Floor Spreading
• 1963 Harry Hess developed the theory of Sea Floor
spreading by applying the discovery of mid-ocean
ridges and trenches
• Mid Ocean Ridges – underwater mountain chains
that run through the Earth’s Basins
• Magma rises to the surface and solidifies and new
crust forms
• Older Crust is pushed farther away from the ridge
• Continuing research led to the development of the
theory of Plate Tectonics
Sea Floor Spreading