#24 Continental Drift to Theory of
Plate Tectonics
Continental Drift was first proposed by Alfred
Wegener.
• looked at a world map and noticed that the
continents appeared to fit together like a
puzzle
• Suggested that continents had once been
connected into one large landmass he
called Pangaea (means “All Land”) about
200 million years ago
Continental Drift Theory states
That continents have moved slowly to their current
locations
• Wegener had evidence to prove his idea but was NOT
able to explain how the continents moved so his
theory was rejected.
Evidence for Continental Drift
1. Puzzle like shape of continents (South America &
Africa)
2. Fossil clues
• Mesosaurus (reptile) fossil found in
Africa & South America
• Glossopteris (fern) fossil found in
Africa, South America, India, Australia,
& Antarctica
3. Climate Clues
• Fossils show that warm climate species
are found in current day cold climates,
fern fossil in Antarctica
• Glacial deposits are found near equator
in South America, Africa, & India
4. Rock Clues
• Similar rock structures are found on
different continents
• Parts of Appalachian Mountains are similar
to mountains in Greenland and Northern
Europe
After Wegener’s tragic death many other
scientists began to expand on his ideas of
Continental Drift and his theory has been
revised to form the Theory of Plate
Tectonics.
These revisions were made possible by
advances in technology.
• SONAR allowed us to make maps of the
ocean floor and oceanographers
discovered seamounts, mid-ocean ridges,
trenches
Mid-Ocean Ridges
• During the 1940’s and 1950’s scientists
began using SONAR to map the ocean
floor
• Harry Hess found many features on the
ocean floor.
• The most important one being the midocean ridge
• A chain of volcanic mountains
• Lava comes out and pushes the plates
apart. This is called Seafloor Spreading.
Paleo-magnetism
https://www.youtube.com/watch?v=WhiF6IqGACo