Chapter 1 Section 3 DRIFTING CONTINENTS The Theory

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 � His 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. 29 � Pangaea existed about 300 million years ago � Tens of millions of years passed while Pangaea broke apart and slowly moved to their present positions; becoming today’s continents.

The Theory of Continental Drift, pg. 29 � Wegener’s idea that the continents slowly moved over Earth’s surface is now known as continental drift. � Wegener studied landforms, fossils and the changes in Earth’s climate to gather evidence for continental drift. �He published “The Origin of Continents and Oceans” in 1915.

Evidence from Landforms, pg. 30 � Mountain 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 Fossils � Wegener 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 Fossils � Glossopteris, 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. 31 � Wegener 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. 31 � When 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. 31 � Another example: South Africa was once covered with continental glaciers �Today’s climate there is mild and wouldn’t allow glaciers to form. �S. Africa must have been closer to the South Pole during this time.

Evidence from Climate, Pg. 31 � As 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 Wegener’s Theory, Pg. 32 � Because Wegener could not identify the cause of continental drift, most geologists rejected his idea from 19201960. � As new evidence surfaces about Earth’s structure, scientists began to reconsider his theory.