continental drift alfred l. wegener untold tragedies of continental drift
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Continental DriftAlfred L. Wegener
Untold tragedies of Continental Drift. .
Alfred L. WegenerAlfred Wegener (1880-1930)Proposed the Theory of Continental Drift - that Earth's continents were originally one land mass. Pieces of the land mass split off and migrated to form the continents.
Since Alfred Wegener's initial theory in 1912, this concept has now proven that the earth's crust is composed of large and small sections called plates.
These plates are different sizes and shapes (like pieces of a jigsaw puzzle); but they are constantly moving. The continents are separate blobs of rock that "float" on the backs of some of the plates.
The continents at one time (about 250 M.Y. ago) were all part of one supercontinent called Pangaea.... which has since split into 7 large pieces that have drifted to their present locations.
The continents are still drifting as the plates continue to move.
How these strange things came to be known and how seemingly unrelated facts and events fit together "hand-in-glove" to constitute what we call plate tectonics this is what makes up the fascinating history of the earth.
The possibility that continents could move was suggested long before anyone could hope to understand or explain how such a thing might be able to occur.
In other words, human knowledge of the forces and processes that govern Earth were virtually unknown. It was simply not possible to prove that continents drifted.
Since the 1950's, enough information began to be accumulate for some patterns to start emerging. Some of these patterns, such as pole reversals and magnetic stripes, now explain what is called sea floor spreading.
Evidence for Continental DriftIt just seems to fit
Continental Driftproposed that the continents were once compressed into a single Supercontinent over time they have drifted apart into their current distributionWegener's hypothesis lacked a geological mechanism to explain how the continents could drift across the earth's surface as he proposed.
Evidence for Continental DriftFit of the ContinentsDistribution of FossilsSimilar sequence of rocks at numerous locationsAncient ClimatesGlaciations
Continental Drift Video Clip
Continental FitThe continents appear to fit together like a puzzle along their coast linesThe Supercontinent was called Pangaea (all lands)
Pangaea was a supercontinent which existed during the Permian Period about 225 million years ago
Fossils of the same species were found on several different continentsFor example, Glossopteris, a fern, was found on the continents of South America, Africa, India, and Australia.If the continents are reassembled into Pangaea, the distribution of Glossopteris can be accounted for over a much smaller contiguous geographic area
Rock sequences in South America, Africa, India, Antarctica, and Australia show remarkable similaritiesWegener proposed that the rock layers were made when all the continents were part of Pangaeathey formed in a smaller contiguous area that was later broken and drifted apart.
Glacier Grooves Kellys Island
Ancient ClimatesGreenland and Antarctica both contain fossils of tropical plants found deep under their ice covered land.
It is believed that these land masses were once located closer to the equator for the tropical plants to have grown here. Therefore, these lands must have moved from the equator area toward the poles.
Problems with Wegener's Model of Continental Drift
Some thought thatDispersion by winds or oceanCurrents could explain theDistribution of fossil specieslack of an adequate mechanism for moving the continents.Wegener proposed that the Earth's spin caused the continents to moveWegener's work was largely unaccepted in the northern hemisphere
1950s 1960s Evidence That Supports the Movement of the PlatesSeafloor Spreading/Subduction