Bell Work 10/16/12 If a theory stated that the continents were all joined together in the past, what evidence would you need to support this theory? Matching coastlines? Matching landforms (mountains, faults, etc)? Climate Evidence? Fossil Evidence? Sea floor evidence?
The Map That Changed the World: Birth of a Theory Intro to Continental Drift
Old Theories The shrinking Earth theory: Earth was molten. It solidifying and shrinking as it cools. Shrinkage of the outer layers causes wrinkles Large wrinkles = continents and ocean basins Small wrinkles = mountain belts Motion is mainly vertical, not horizontal. Continents are drained as ocean basins warp down, and flooded as they fill with sediment.
What James Hutton Saw . . .
“The present is the key to the past” Uniformitarianism Coined by James Hutton to explain that the Earth was older than 6,000 yrs. Suggests that all of Earth’s geological features and history can be explained by processes identical to ones acting today. These processes have been at work for a very long time. “The present is the key to the past”
Alfred Wegener German meteorologist. Explored Antarctica, Greenland and S. America. In 1912 wrote article describing his theory of Continental Drift. States: 200 Ma all continents were connected as one supercontinent called Pangaea. Continents plowed through ocean floor.
Evidence for Continental Drift Wegener’s evidence: Apparent “fit” of continents Distribution of fossils Similar rocks and mountain ranges Climatic evidence
Puzzle Fit of Continents Noticed 3 centuries earlier, Wegener used the close fit of S. America to Africa as evidence the continents were once joined and drifted apart. Geological structures such as folds and faults match-up.
Fossil Evidence Several 200 Ma fossils of plants and animals can be found on many of the southern continents such as S. America, Africa, Antarctica, India and Australia. Fossils such as: Glossopteris (plant) Mesosaurus (animal) Lystrosaurus (animal)
Glossopteris Fossils of this plant species has been found on all southern continents. Wegener’s evidence: plant could not colonize across an ocean survive in Antarctic climate.
Mesosaurus Aquatic reptile found in S. America and Africa. Lived in shallow fresh water swamps. Wegener reasoned mesosaurus could not migrate across an ocean basin.
Lystrosaurus Short-legged mammal-like reptile who’s fossils are found in India, Africa, and Antarctica. Wegener reasoned lystrosaurus could not swim across an intervening ocean.
To Wegener, the only explanation could be . . .
Similar Mountain Ranges Mountain range composition, age, and structure are very similar across the Atlantic. Wegener was convinced that the Appalachian Mountains of eastern US were related to the Atlas Mountains in N. Africa.
Climatic Evidence Coal deposits found on Antarctica. Coal forms from millions of years of tropical plant decay (buried rainforests). Wegener reasoned that Antarctica must have been near the equator at one time in the geologic past.
Climatic Evidence Glacial deposits and glacial striations were discovered in S. America and Africa (near equator). Direction of glacial striations disobeyed the laws of gravity.
Glacier Striations Striations show direction of ice movement. Striations are evidence of glaciers.
Evidence of Glaciers
Gondwanaland Glaciations
Wegener’s Fatal Flaw When asked by his peers “What was the mechanism that moved the continents across the Earth?” Wegener stated that the spin of the Earth caused the continents to move (WRONG!). Physicist proved that the force of the continents plowing through the ocean floor would break the continents up into small pieces.
Fate of the Theory of Continental Drift Scientific community of 1912 was not ready to accept Wegener’s “crazy & preposterous” ideas. For the rest of his life, Wegener devoted himself to proving his Theory of Continental Drift. Unfortunately Wegener froze to death in Greenland in 1930. Little did he know that he was far ahead of his time.