1. Topic: Continental Drift
PSSA: A / S8.D.1.1

2. Objective: TLW describe Wegener’s theory of continental drift.
TLW identify fossil evidence for continental drift.
TLW describe sea-floor spreading as a mechanism for continental drift.

3. MI #1: What is Continental Drift?
Continental drift is the hypothesis that all of Earth’s continents once formed a single landmass (called Pangaea), broke apart, and drifted to their present locations.
Alfred Wegener was the scientist who first proposed this theory.

4. MI #2: Continental Drift – Visual Evidence
One reason Wegener developed this theory is that the Earth’s continents (especially South America and Africa) look like they could fit together much like a giant jigsaw puzzle.

5. MI #3: Continental Drift – Fossil Evidence
Mesosaurus was a small aquatic reptile whose fossils have been found on S. America and Africa.
Glossopteris, a prehistoric plant, has fossils that have been found on S. America, Africa, Australia, and Antarctica.

7. MI #4: What are tectonic plates?
Tectonic plates are large pieces of the lithosphere that float on top of the asthenosphere.
The entire surface of the Earth (continental and oceanic) is divided into tectonic plates.

8. MI #5: Sea-floor Spreading
The process by which new oceanic lithosphere is formed as magma rises to the surface at mid-ocean ridges.
As the magma comes to the surface old oceanic crust is pushed further away from the mid-ocean ridge.

10. MI #6: Magnetic Reversals
Magnetic reversals are points in the Earth’s geologic history where the polarity of the Earth’s magnetic poles changes.
These reversals are recorded in the orientation of magnetic minerals (like iron) in the oceanic crust, providing evidence for sea-floor spreading.

11. So What…? Real Life Application
Understanding continental drift and sea floor spreading are foundational in understanding the theory of plate tectonics, which explains mountain building, earthquakes, and volcanoes.