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

225 Million Years Ago

USGS

PANGAEA SUPER-CONTINENT180 million years ago

135 million years ago

65 million years ago

Our world today

GLACIAL EVIDENCE• matching glacial

deposits found on different continents

• Matching glacial striations (grooves) on different continents

FOSSIL EVIDENCE

ROCK EVIDENCE• alignment of continental shelves

• Matching of unique rock types across continents

MOUNTAIN BELTS EVIDENCE

Ranges with the same ages of deformation on opposite sides of ocean

Appalachians (N. America) line up with Caledonides (Britain & Scandanavia)

Wegener’s Hypothesis Rejected

Continental Drift Hypothesis was rejected because

Wegener had no working driving mechanism for continental movement

Continental Drift Hypothesis turns into

Plate Tectonic Theory

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 . . .

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

Deep Sea Trenches & Ridges

Pearson Prentice Hall

EVIDENCE:

World wide distribution

of earthquakes

and volcanoes

EVIDENCE: Paleomagnetism

Earth acts like a magnet Normal polarity: north = magnetic pole Reverse polarity: south = magnetic pole

Paleomagnetism

Magnetometers recorded strange strips on ocean floor

Stripes represented flips in Earth’s polarity

Stripes symmetrical across ridges

PaleomagnetismCooling magma records polarity

EVIDENCE:Age of Ocean Rocks