Drifting Continents

1. Drifting Continents Key Terminology • Hypothesis- a proposal intended to explain certain facts or observations, but that is not yet verified. • Theory- a hypothesis that survives experimental testing becomes a scientific theory" • Plate- a large, rigid slab of solid rock. Tectonics "to build." • The theory of plate tectonicsstates that the Earth's outermost layer is fragmented into a dozen or more large and small plates that are moving relative to one another as they ride atop hotter, more mobile material. • Continental drift was the forerunner of plate tectonics.

2. Concepts and Terms • Focus Questions • What was Alfred Wegener’s hypothesis about continental drift? • What evidence supported Wegener’s hypothesis? • Why was Wegener’s hypothesis rejected by most scientists of his day? • Terms • Continental Drift • Pangaea • Fossil

3. Hypothesis: All the continents were once joined together in a single landmass and have since drifted apart. Supercontinent Pangaea Wegener thought that over tens of millions of years, Pangaea began to break apart. The pieces of Pangaea slowly moved toward their present day locations becoming the continents they are today. This idea became known as Continental Drift 1912- Alfred Wegener proposed the hypothesis of continental drift.

4. Supercontinent

5. 200 million years ago Pangaea began to break apart.

9. Continental Drift • Wegener gathered evidence from different scientific fields to support his ideas about continental drift. He studied land features, fossils, and evidence of climate change.

10. Evidence from land features • If maps of Africa and South America are pieced together, mountain ranges on both continents line up. • European coal fields match up with similar coal fields in North America.

11. Evidence from Fossils • Similar fossils on different continents • What is a fossil? • Any trace of an ancient organism preserved in rock. • How did Wegener explain similar fossils on different continents? • The organisms lived on a single landmass that has since split apart.

12. Plant and animal fossils

13. Evidence from Climate • Climate doesn’t match fossil records. • What would explain tropical foliage fossils found in Alaska? • Either the climate of the Earth was different when the palms grew 60 million years ago or else the rocks in which the fossils occur moved in from someplace else. • Wegener believed that continental drift explained fossils of tropical plants are found in places that today have polar climates.

14. Glacier movement match

15. Wegener’s Hypothesis Rejected • Unfortunately, Wegener could not provide a satisfactory explanation for the force that pushes or pulls the continents. • Because he could not identify the cause of continental drift, most geologists rejected his idea.

16. Hypothesis Rejected • How did he think mountains formed? • He proposed that when continents collide their edges crumble and fold. • The folding continents push up huge mountains. • How did the locations of mountains support his idea of how mountains formed? • Mountains sometime occur on narrow bands along the edges of continents where continents collide.

17. What evidence was he missing for it to be accepted as a theory? • Wegener failed to prove how the plates moved. • He proposed that the continents move by plowing through the rock. • Use of sonic instruments to map the ocean floor lead to the discovery of Sea-floor Spreading.