1. Chapter 10-1
Continental Drift

2. CONTINENTAL DRIFT THEORY-
Wegener’s Hypothesis
CONTINENTAL DRIFT THEORY-
Hypothesis that a large single landmass broke up into smaller landmasses to form the continents, which then drifted to their present location.

3. Wegener’s Evidence
Fossil evidence-
Rock formation-
Climatic evidence-

4. MID-OCEAN RIDGES
Undersea mountain ranges through the center of which run steep, narrow valleys.
Forms as magma rises from the asthenosphere and creates new lithosphere as tectonic plates move apart.

5. Mid-Ocean Ridge

6. Mid-Atlantic Ridge

7. About Mid-Ocean Ridges
The sediment that covers the sea floor is thinner closer to the ridge than it is farther away from the ridge.
Close to ridge – thin layer of sediment
Farther from ridge- thicker layer of sediment

8. Closer to the ridge- younger sea floor
And more……..
Closer to the ridge- younger sea floor
Farther from the ridge- older sea floor
Ocean floor rocks are less than 200 million years old!

10. Sea Floor Spreading Harry Hess’ s hypothesis
At the center of the mid-ocean ridge is a RIFT.
Molten rock rises to fill the crack.
As the ocean floor moves away from the ridge, magma cools and solidifies creating new rock that replaces the ocean floor.
Named Sea Floor Spreading by Robert Dietz

11. If the sea floor is spreading, is the Earth getting bigger?NO

13. In the mid 1960’s more evidence for sea floor spreading was found.
PALEOMAGNETISM- THE STUDY OF THE ALIGNMENT OF THE MAGNETIC MINERALS IN ROCK, specifically as it relates to the reversal of the Earth’s magnetic poles; also the magnetic properties that rock acquires during rock formation.

14. Paleomagnetism Earth acts as a giant magnet
Earth has north and south geomagnetic poles
As magma solidifies to form rock, the iron-rich minerals in the magma align with Earth’s magnetic field, like a compass.
When the rock hardens this magnetic orientation becomes permanent.

15. GEOMAGNETIC REVERSAL TIME SCALE
Evidence shows Earth’s magnetic field has not always pointed north
Rocks were discovered whose magnetic orientations point opposite to Earth’s current magnetic field.
Rocks with magnetic fields pointing north have NORMAL POLARITY
Rocks with magnetic fields pointing south have REVERSED POLARITY.

16. Scientists placed these periods of reversal in chronological order and discovered an alternating pattern

17. Scientists discovered reversals in rocks on land also.
They matched the pattern of reversal with the ages, they were confident that magnetic patterns show changes over time.
CONCLUSION: Sea floor spreading provides the mechanism for the continents to move over Earth’s surface.