Continental Drift __________________THEORY
Today’s Objectives • be able to describe the Continental Drift Theory • be able to describe the evidence for the Continental Drift Theory including: • Jigsaw puzzle fit of continents • Geological structures • Fossils • Climatic evidence
Continental Drift… • This theory was proposed by Alfred Wegener, a German scientist about 100 years ago. • He hypothesized that the continents were not always in the same location that they are today, but that they have “drifted” there over millions of years.
He proposed that millions of years ago – the continents were all attached in one “super-continent” called PANGAEA. In Greek: • Pan – means “all” • Gaea means “Earth”
His theory of what happened… • 250 million years ago, was Pangaea • 220 million years ago… it started to drift apart.
Continental Drift Theory • the continents are still moving today
How did he come up with this theory… Evidence. • #1:He looked at maps of the world and noticed all the continents looked like puzzle pieces that “fit together”. North America Africa South America
#2- Matching Geologic Structures • Mountain Ranges: He noticed that mountain ranges that began on one continent, then ended at the coast-line, seemed to continue on another continent across the Ocean!
Matching Geologic Structures • Rock structures: such as Folds in the Earth’s crust, and the types of rocks were similar on different continents • Eg. Rocks found in Newfoundland (North American continent) are the same type and age as rocks found in Greenland and Ireland/Scotland (European Continent) • Giant’s Causeway • (Ireland and Scotland)
#3- Matching Fossils • Wegener found that similar fossils are found on different continents despite the continents being separated by vast oceans • How did the creatures get between the continents? • Creatures could not swim or fly that great of distance • Most likely explanation = continents were closer together at some point in time
#3- Matching Fossils • One fossil that intrigued him was Mesosaurus(a sharp-toothed freshwater reptile). These fossils have only been found in 2 places – Southeastern “South America” and Southwest “Africa”
There were many other fossils where he found the same thing. • Gossopteris(a fern). It’s fossils were found on every continent including Antarctica…It can’t grow in cold temperatures, so Antarctica must have been warmer millions of years ago because it must have been closer to the equator.
Cynognathus and Lystrosaurus(land dwelling creatures) Fossils found on different continents. They could not have swam that far to get onto different continents …so the continents must have been joined.
#4- Climatic Evidence Paleoglaciation • Rock markings left behind from ancient glaciers suggest tropical regions may have once been more polar (allowing for the formation of glaciers) • This suggests that the continents were once closer together
More Climatic Evidence Coal deposits • coal is formed from decay of tropical plants • coal deposits are found in Antarctica • suggests Antarctica was once a tropical climate that was closer to the equator 19
Summary of Evidence for Continental Drift… • 1) Map show that continents fit together like puzzle pieces • 2) Mountain ranges that seem to be split between 2 distant continents • 3) Fossils found on different continents • 4) Climatic patterns that make sense if continents were once connected. • Paleoglaciation • Coal Deposits