Continental Drift

Pangaea  Nearly 100 years ago, Alfred Wegener began an investigation that continues even today.  He wanted to know if Earth’s continents were in fixed (non-moving) positions.  He proposed that all the continents were once part of a supercontinent called Pangaea.  Wegener proposed the hypothesis of continental drift.  This hypothesis suggested that the continents of Earth are in constant motion on the surface of Earth.  Over time, the continents slowly drifted to their current positions from the supercontinent, Pangaea.

Evidence that Continents Move  Puzzle-Like Fit of the Continents  Many of the continents look as if they could fit together like a giant puzzle.

Evidence that Continents Move  Climate Clues  Fossils of warm-weather plants  Tropical plant fossils were found on an island in the Arctic. This meant that this area had to have drifted from somewhere warmer to its current much colder location.  Glaciers  Evidence of glaciers have been found in temperate and tropical areas. How do you explain glacial deposits (evidence of glaciers) in areas where no glacier could possibly exist today?  Wegener thought that finding examples of tropical fossils in regions where they shouldn’t be able to exist and finding evidence of glaciers in areas where they couldn’t exist, tells us that the Earth was dramatically different in the past.

Evidence that Continents Move  Fossil Clues  Mesosaurus  Fossils of Mesosaurus have been found in Africa and South America. This animal lived in fresh water and on land. How could these fossils be found on land areas separated by a large ocean of salt water?  Wegener believed that the continents being connected previously would explain this occurrence.  Glossopteris  A plant fossil found in Africa, Australia, India, South America, and Antarctica.  Wegener believed that because this fossil was so wide-spread (existed on many continents), the only way that this could occur would be if the continents had once been connected.  Wegener believe that the Mesosaurus lived on both continents while they were still joined. Also, the presence of glossopteris in so many areas supported Wegener’s idea that all of these regions were once connected and had similar climates.

Evidence that Continents Move  Rock Clues  If the continents were once connected, then the rocks that make up the continents should be the same in locations where they were joined. Similar rock structures have been found on different continents.

Why Continental Drift was not Accepted  Evidence  Wegener had plenty of evidence to imply that continents were on the move.  Wegener could not explain what forces could possibly cause the continents to move.  Evidence necessary to prove continental drift was not discovered until long after Wegener had died.

REVIEW 1.What was the name of the scientist that developed the idea of continental drift? 2.What is Pangaea? 3.What is continental drift? 4.What evidence did Wegener use to support the idea of continental drift? 5.What was the primary reason most scientist did not believe in Wegener’s idea of continental drift?