Continental Drift Chapter 9.1

Proposed by Alfred Wegener in 1912 250 million years ago there was a SUPERCONTINENT called PANGAEA

Pangaea then broke up into Laurasia Gondwanaland

Pangaea splits to form: Laurasia= Europe, Asia, & North America Gondwanaland= South America, Africa, Australia, Antarctica, Madagascar, & India

“PROVE IT!!!!!!!!!!” Geologists said… …and he said “Ok, here’s my 4 forms of evidence”

Evidence to Support Continental Drift

1. “Puzzle Pieces” Continents look like they could be part of a giant jigsaw puzzle

2. Distribution of Fossils Plant & animal fossils found on the coastlines of different continents

Example: Fossil clues (Ex. Mesosaurus) -organisms couldn’t swim across. -fossils would have been found all over the globe if they could swim Critics argued that the animal could have walked across a land bridge Wegener argued back – if there was a land bridge there would be remnants of it still around - No remnants = no land bridge!

3. Rock Types & Structures Several mountain ranges end at one continents edge and reappear at the edge of another continent What does that imply? This implies that the continents were once connected

4. Ancient Climates Glacial sheets have been found in Africa, South America and other areas These sheets show that 200-300 mya ice covered these areas. These areas are very close to the Equator If the continents have always been at their present locations, it could NEVER have been cold enough for this ice to form In Pangaea, these areas were close to the Antarctic Pole

They also found coal in Antarctica! * What does that imply? There would have had to have been a forest that grew there. Had to have been warm at some point. At the present location that would be impossible!!

The Geologists reject Wegener’s hypothesis! He hasn’t explained HOW the continents are moving!

He thought the continents just simply floated along on top of the oceans. NOT TRUE!!! Wegener’s evidence was CORRECT!! He just couldn’t explain HOW the continents moved

SONAR – bouncing radio waves off of the ocean floor A NEW HOPE!!! Technology gets us better info on the ocean floor, earthquakes, and the planet’s magnetic field! Leads us to… 1968- The Theory of Plate Tectonics Note: It took 56 years to come up with the new accepted theory. SONAR – bouncing radio waves off of the ocean floor

Plate Tectonics We will cover this tomorrow!