Title: Chapter 17 Plate Tectonics; 17.1 Drifting Continents

Page: 85Date: 3/11/2013

Students will be able to identify lines of evidence that led Wegener to suggest that Earth’s continents have moved.

Students will be able to discuss evidence of ancient climates supported by continental drift.

Students will be able to explain why continental drift was not accepted when it was first proposed.

Hypothesis: A testable explanation of a situation.

Main Idea: The shape and geology of the continents suggests that they were once joined together.

Early Observations:

First evidence from cartographers (map makers.)

Noticed continents fit together like puzzle pieces.

1500s Abraham Ortelius (Dutch) proposed that North and South America had been separated from Europe and Africa by earth quakes and floods.

Abraham Ortelius 1858 Continental Puzzle Map

Early Observations:

1912 Alfred Wegener (German) made 1st scientific proposal.

Alfred Wegener(Looks like Mr. Martino)

Continental Drift

Wegener’s theory: Continents were once

joined as a single land mass called Pangaea “All Earth.”

Pangaea broke up 200 million years ago.

Continents have been moving ever since.

Pangaea

Evidence (3 Pieces)

1. Evidence from Rock Formations: • Wegener found identical

rock layers in Appalachian Mountains, Greenland and Europe - all older than 200 million years.

Rock Layer Evidence of Continental Drift

Evidence (3 Pieces)

2. Evidence from Fossils: • Wegener found fossils of

similar land animals and plants on different continents.

• No way land animals could have swam across oceans.

Fossil Evidence of Continental Drift

Fossil Evidence of Continental DriftMesosaurus (An aquatic reptile that Wegener believed wasNot able to swim across an entire ocean.)

Evidence (3 Pieces)

3. Climatic Evidence: • Fossil of plant Glassopteris

found in South America, Antarctica and India.

• Plant only grows in warm climates.

• Climates on these continents must have been different - warmer.

Evidence (3 Pieces)

3. Climatic Evidence: Coal Deposits: Coal forms from the

compaction and decomposition of accumulations of ancient tropical swamp plants.

Coal deposits found in Antarctica.

Antarctica must have had a tropical climate - must have been closer to the equator.

Pangaea Coal Deposits

Evidence (3 Pieces)

3. Climatic Evidence: Glacial Deposits: Found 290 million year old

glacial deposits in Africa, India, South America and Australia.

Current locations of these continents are too warm for glaciers.

Continents must have once been closer to South Pole.

Evidence from Glacial Deposits

A Rejected Notion

• 1900s Scientists thought continents had been carved out by erosion and rejected Wegener’s theory of Continental Drift.

• 2 Questions Wegener could not explain:

1. What forces caused continents to move?

2. How could continents move through solids?

• Not until WWII when technology was developed that Wegener’s hypothesis was taken seriously.