The main features are:
* The Earth's surface is made up of a series of large plates (like pieces of a giant jigsaw puzzle).
* These plates are in constant motion traveling at a few centimeters per year.
* The ocean floors are continually moving, spreading from the center and colliding with the edges of the plates. As the sea-floor spreads from the magma source (where new crust is being created) it becomes older crust. Which is known as sea-floor spreading.
* Convection currents beneath the plates move the plates in different directions.
* The source of heat driving the convection currents is radioactive decay which is happening deep within the Earth.
* At the edges of these plates intense geologic activity such as earthquakes, volcanoes, and mountain building occur.
* Plate tectonics is a relatively new theory and it wasn't until the 1960's that geologists, with the help of ocean surveys, began to understand what goes on beneath our feet.
Alfred Wegner's Theory of Continental Drift
A scientist by the name of Alfred Wegner wrote his theory of continental drift in the early 1900’s. His theory explained a lot of the puzzling observations, including the almost perfect fit of the continents. The theory of continental drift explained why some fossils of the same plant and animal species are found along coastlines on different continents. Some fossils of species that could not fly or swim were found on different continents. The question remains, “How did that happen?”
245 million years ago all of the continents were one piece of land, Pangea. Many scientist didn’t think that Wegner’s theory was a proven theory. Scientists later speculated that the reasoning of this fossil mystery is sea- floor spreading. Sea-floor spreading takes place on the mid-ocean ridges.
245 Million years ago: Pangaea existed when some of the earliest dinosaurs were roaming around this big earth. The land Pangaea was surrounded by a sea called Panthalassa.
180 million years ago: Pangaea slowly broke into two big pieces. The northern piece was called Laurasia. The southern piece was called Gondwana.
65 million years ago: By the time the dinosaurs became extinct, Laurasia and Gondwana had spilt into smaller pieces which are now known as continents.
Definitions:
Continental drift: is the theory that Continents can drift apart from one another and have done so in the past.
Pangaea: is the Greek word “all earth”
Sea-floor spreading: is the process by which new oceanic lithosphere is created as older materials are pulled away.
Mid-ocean ridges- are underwater mountain chains that run through earth’s ocean basins.
Panthalassa: was the sea that surrounded Pangaea 245 million years ago. The word Panthalasa meant “all sea”.
Laurasia: Was the Northern piece of Pangaea when it split in half.
Gondwana: Was southern piece of Pangaea when it split in half.
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