Chapter 1 Section 3. Drifting Continents. The Theory of Continental Drift, pg. 29. In 1910 a German scientist named Alfred Wegener formed a hypothesis that the Earth’s continents had moved from their original position. Alfred Wegener. The Theory of Continental Drift, pg. 29. - PowerPoint PPT Presentation
Text of Drifting Continents
Chapter 1 Section 3
The Theory of Continental Drift, pg. 29In 1910 a German scientist named Alfred Wegener formed a hypothesis that the Earths continents had moved from their original position. Alfred Wegener
The Theory of Continental Drift, pg. 29His hypothesis stated that all the continents had once been joined together in a single landmass and has since drifted apart. Wegener named this super continent Pangaea, meaning All Lands.
The Theory of Continental Drift, pg. 29Pangaea existed about 300 million years agoTens of millions of years passed while Pangaea broke apart and slowly moved to their present positions; becoming todays continents.
The Theory of Continental Drift, pg. 29Wegeners idea that the continents slowly moved over Earths surface is now known as continental drift.Wegener studied landforms, fossils and the changes in Earths climate to gather evidence for continental drift. He published The Origin of Continents and Oceans in 1915.
Evidence from Landforms,pg. 30Mountain ranges and other features on the continents provided evidence for continental drift. Mountain ranges in South Africa match up to mountain ranges in Argentina when pieced together. European coal fields match up with similar coal fields in North America.
Evidence from FossilsWegener also used fossils, any trace of an ancient organism that has been preserved in rock, to support his theory.Fossils of reptiles Mesosaurus and Lystrosaurus have been found in places now separated by oceans. Neither could have swam great distances across salt water, therefore they must have lived on a single landmass that has since been split apart.
Evidence from FossilsGlossopteris, a fern-like plant, lived over 250 million years ago. Fossils have been found in Africa, South America, Australia, India and Antarctica. The presence on widespread landmasses convinced Wegener that the continents were once connected. Its seeds were too large to have been carried by the wind, and too fragile to have survived travel by ocean waves.
Evidence from Climate, Pg. 31Wegener used evidence of climate change to support his theory of continental drift. Example: The island of Spitsberger lies in the Arctic Ocean, North of Norway. It is ice-covered and has a harsh polar climate. But fossils of tropical plants have been found on Spitsberger.
Evidence from Climate, Pg. 31When these plants were alive 300 million years ago, the island must have had a warm and mild climate (closer to the equator).
Evidence from Climate, Pg. 31Another example: South Africa was once covered with continental glaciersTodays climate there is mild and wouldnt allow glaciers to form. S. Africa must have been closer to the South Pole during this time.
Evidence from Climate, Pg. 31As continents move towards the poles, climate becomes colder. As continents move towards the equator, climate becomes warmer. But continents carry, with it, fossils and rocks formed at its previous locations.
Scientists Reject Wegeners Theory, Pg. 32Because Wegener could not identify the cause of continental drift, most geologists rejected his idea from 1920-1960. As new evidence surfaces about Earths structure, scientists began to reconsider his theory.