Continental DriftContinental Drift
Alfred L. Wegener
Untold tragedies of Continental Drift. .
Alfred L. WegenerAlfred L. Wegener Alfred 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 DriftEvidence for Continental Drift
It just seems to fit
Continental DriftContinental Drift proposed that the continents were once
compressed into a single Supercontinent
over time they have drifted apart into their current distribution
Wegener's hypothesis lacked a geological mechanism to explain how the continents could drift across the earth's surface as he proposed.
Evidence for Continental DriftEvidence for Continental Drift
Fit of the ContinentsDistribution of FossilsSimilar sequence of rocks at
numerous locationsAncient ClimatesGlaciations
Continental Drift Video ClipContinental Drift Video Clip
Continental FitContinental Fit The continents
appear to fit together like a puzzle along their coast lines
The Supercontinent was called Pangaea (all lands)
Pangaea was a supercontinent which existed during the Permian Period about 225 million
years ago
Pangaea was a supercontinent which existed during the Permian Period about 225 million
years ago
Fossil DistributionFossil Distribution Fossils of the same
species were found on several different continents
For 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/MountainsRock Sequences/Mountains
Rock sequences in South America, Africa, India, Antarctica, and Australia show remarkable similarities
Wegener proposed that the rock layers were made when all the continents were part of Pangaea
they formed in a smaller contiguous area that was later broken and drifted apart.
Glacier GroovesGlacier Grooves
Glacier Grooves – Kelly’s IslandGlacier Grooves – Kelly’s Island
GlaciationsGlaciations
•
Ancient ClimatesAncient Climates Greenland 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
Problems with Wegener's Model of Continental Drift
Some thought thatDispersion by winds or
oceanCurrents could explain theDistribution of fossil species
lack of an adequate mechanism for moving the continents.
Wegener proposed that the Earth's spin caused the continents to move
Wegener's work was largely unaccepted in the northern hemisphere
1950’s 1960’s Evidence That Supports the Movement of the Plates
1950’s 1960’s Evidence That Supports the Movement of the PlatesSeafloor Spreading/Subduction
Paleomagnetism
Seismic Data
