Physical Geology 101
Jigsaw Puzzle Continents
Mapmakers and geographers had noted that the continental coasts of Africa and South America are similar as early as the 1600's.
What is the significance of this observation?
Alfred Wegener, in 1915, used this and other evident to support his ideas on Continental Drift.
Wegener proposed that at one time all of the continents were part of one land mass called Pangaea - a supercontinent.
Beginning approximately 200 million years ago the continents began to move or drift apart to their present day positions.
The remainder of the Earth's surface was one large ocean.
Evidence For Continental Drift
6 main pieces of evidence were presented by Alfred Wegener
Jigsaw puzzle fit of the continents
Similar rock types
Glacial and climatic evidence
Jigsaw Puzzle Fit
East coast of South America and the west coast of Africa.
Not an exact fit.
Similar Rock Types
The continents define the shape of the puzzle piece, while the rocks that make up the continent define the "picture" for each piece.
Rocks found in Africa's west coast are the same rock types - are the same rocks - that are found along the east coast of South America
South Africa and west Africa are rich in mineral ores.
Many of these ore deposits occur in linear deposits that can be traced to the edge of the continent, then abruptly end.
Some of these mineral belts can be traced over to South America
Appalachian Mountains extend from Georgia to Newfoundland in North America
When North America and Europe are moved back together, the Appalachians form a continuous mountain belt with the highlands in Scotland and the coastal range of Scandinavia.
Fossils are remains or traces of ancient life
Some fossil organisms are found in rocks widely distributed on many continents.
This usually indicates an organism that was living in marine conditions and was deposited in sediments along the coasts of many continents.
Some fossils are of terrestrial organisms and have a more restricted distribution.
Mesosaurus - aquatic reptile, found only in eastern South America and southern Africa.
Glossopteris – cold climate, large seed, fossil fern found in Africa, Australia, India, Antarctica and South America.
How does this support Continental Drift?
Glacial and Climate Data
Ancient glacial deposits and striations are found in southern South America, southern Africa, southern India and southern Australia
Wegener's diverse evidence all pointed to the conclusion that the continents had once been part of a much larger continent.
How did the continents move?
Problems with Motivation
Researchers quickly calculated the forces involved in these two mechanisms and concluded:
Rejection of Continental Drift
Many scientists rejected Wegener's theory because of:
The evidence Wegener used is correct and the basic premise of Continental Drift is correct - at one time all of the continents were part of one land mass called Pangaea and approximately 200 million years ago the continents began to move or drift apart to their present day positions.
The proposed model for motivation was wrong.
The theory was widely debated for decades but lacked sufficient data to convince everyone of its validity.
What more is needed?