Page 1
CONTINENTAL DRIFTAlfred Wegener (1915) introduces CONTINENTAL
DRIFT HYPOTHESIS. Super-continent Pangaea separated 200 million years ago.
Evidence:Fit of the continentsContinuity of mountain beltsGlaciationFossil evidenceDiversity of species
USGS
Page 2
225 Million Years Ago
USGS
Page 3
PANGAEA SUPER-CONTINENT180 million years ago
Page 4
135 million years ago
Page 5
65 million years ago
Page 7
GLACIAL EVIDENCE• matching glacial
deposits found on different continents
• Matching glacial striations (grooves) on different continents
Page 9
ROCK EVIDENCE• alignment of continental shelves
• Matching of unique rock types across continents
Page 10
MOUNTAIN BELTS EVIDENCE
Ranges with the same ages of deformation on opposite sides of ocean
Appalachians (N. America) line up with Caledonides (Britain & Scandanavia)
Page 11
Wegener’s Hypothesis Rejected
Continental Drift Hypothesis was rejected because
Wegener had no working driving mechanism for continental movement
Page 12
Continental Drift Hypothesis turns into
Plate Tectonic Theory
Page 13
Plate Tectonic Theory Evidence
Ocean floor was mapped Earthquake & volcano distribution
determined Paleomagnetism discovered Age of the ocean floor determined Hot Spots discovered And more . . .
Page 14
EVIDENCE:Mapping of the ocean floor
Began in the 1950’s and led to the discovery of:
Deep ocean trenches Submerged volcanic
island chains Extensive mountain
systems on the ocean floor USGS
Page 15
Deep Sea Trenches & Ridges
Pearson Prentice Hall
Page 16
EVIDENCE:
World wide distribution
of earthquakes
and volcanoes
Page 17
EVIDENCE: Paleomagnetism
Earth acts like a magnet Normal polarity: north = magnetic pole Reverse polarity: south = magnetic pole
Page 18
Paleomagnetism
Magnetometers recorded strange strips on ocean floor
Stripes represented flips in Earth’s polarity
Stripes symmetrical across ridges
Page 19
PaleomagnetismCooling magma records polarity
Page 20
EVIDENCE:Age of Ocean Rocks