|You might also like:||Pangaea||The Continents: Extremes||Continents||Label Continents Map Printout||Table of the Continents - Reading and Understanding Tables, A Printable Worksheet||Today's featured page: King Tut Coloring Page|
|Our subscribers' grade-level estimate for this page: 4th - 5th|
Dinosaur and Paleontology Dictionary
|CONTINENTAL DRIFT||Go to an interactive plate tectonics puzzle|
In 1915, the German geologist and meteorologist Alfred Wegener
first proposed the theory of continental drift, which states that parts of the Earth's crust slowly drift atop a liquid core. The fossil record supports and gives credence to the theories of continental drift and plate tectonics.
Wegener hypothesized that there was a gigantic supercontinent 200 million years ago, which he named Pangaea, meaning "All-earth".
Pangaea started to break up into two smaller supercontinents, called Laurasia and Gondwanaland, during the Jurassic period. By the end of the Cretaceous period, the continents were separating into land masses that look like our modern-day continents.
Wegener published this theory in his 1915 book, On the Origin of Continents and Oceans. In it he also proposed the existence of the supercontinent , and named it (Pangaea means "all the land" in Greek).
Glossopteris, a tree-like plant from the Permian Period through the Triassic Period. It had tongue-shaped leaves and was about 12 ft (3.7 m) tall. It was the dominant plant of Gondwana.
Fossils of Mesosaurus (one of the first marine reptiles, even older than the dinosaurs) were found in both South America and South Africa. These finds, plus the study of sedimentation and the fossil plant Glossopteris in these southern continents led Alexander duToit, a South African scientist, to bolster the idea of the past existence of a supercontinent in the southern hemisphere, Eduard Suess's Gondwanaland. This lent further support to A. Wegener's Continental Drift Theory
|Type of Crust||Average Thickness||Average Age||Major Component|
|Continental Crust||20-80 kilometers||3 billion years||Granite|
|Oceanic Crust||10 kilometers||Hundreds of millions of years||Basalt|
The top layers of the plates are called the crust. Oceanic crust (the crust under the oceans) is thinner and denser than continental crust. Crust is constantly being created and destroyed; oceanic crust is more active than continental crust.
TYPES OF PLATE MOVEMENT: Divergence, Convergence, and Lateral Slipping
At the boundaries of the plates, various deformations occur as the plates interact; they separate from one another (seafloor spreading), collide (forming mountain ranges), slip past one another (subduction zones, in which plates undergo destruction and remelting), and slip laterally.
Divergent Plate Movement: Seafloor Spreading
Seafloor spreading is the movement of two oceanic plates away from each other, which results in the formation of new oceanic crust (from magma that comes from within the Earth's mantle) along a a mid-ocean ridge. Where the oceanic plates are moving away from each other is called a zone of divergence. Ocean floor spreading was first suggested by Harry Hess and Robert Dietz in the 1960's.
|Convergent Plate Movement:|
When two plates collide, some crust is destroyed in the impact and the plates become smaller. The results differ, depending upon what types of plates are involved.
Oceanic Plate and Continental Plate - When a thin, dense oceanic plate collides with a relatively light, thick continental plate, the oceanic plate is forced under the continental plate; this phenomenon is called subduction.
Two Oceanic Plates - When two oceanic plates collide, one may be pushed under the other and magma from the mantle rises, forming volcanoes in the vicinity.
Two Continental Plates - When two continental plates collide, mountain ranges are created as the colliding crust is compressed and pushed upwards.
|Lateral Slipping Plate Movement:
When two plates move sideways against each other, there is a tremendous amount of friction which makes the movement jerky. The plates slip, then stick as the friction and pressure build up to incredible levels. When the pressure is released suddenly, and the plates suddenly jerk apart, this is an earthquake.
|The Mesozoic Era
248 - 65 million years ago - The Age of Reptiles
|The Triassic Period
248 - 206 million years ago
|The Jurassic Period
206-144 million years ago
|The Cretaceous Period
144-65 million years ago
Over 35,000 Web Pages
Sample Pages for Prospective Subscribers, or click below
Overview of Site|
Enchanted Learning Home
Monthly Activity Calendar
Books to Print
Parts of Speech
The Test of Time
TapQuiz Maps - free iPhone Geography Game
Biology Label Printouts
Physical Sciences: K-12
Art and Artists
Label Me! Printouts
|Search the Enchanted Learning website for:|