Plate Tectonics

A Tectonic Plate is a huge slab of solid rock. Tectonics, from the Greek, means build. Thus “plate tectonics” is the study of building the earth with large slabs of rock which float on a hot, mobile mantle.The plates move slowly and independently, often times bumping in to each other. When you looked at globe of the earth or a large map in Grammer School you must have noted that Africa and South America looked as if they had been joined at one time.

Alfred Wegener, born in 1830, noted this peculiarity and also discovered many forms of life which were the same on both sides of the South Atlantic. Using this as well as much more information about rock formations which were also the same on both sides he decided that the continents were drifting away from each other, an idea which was called the theory of contintental drift and intensely ridiculed at the time. His theory was essentially correct but he could not come up with a physical mechanism which would explain the drift. Wegener died in the Arctic in 1930 before his ideas were vindicated.

According to Continental Drift Theory, all of the world’s continents were joined in a Super Continent called Pangea, in the Permian era, 225 million years ago (MYA). Pangea broke up in the Triassic period about 200 MYA, into continents called Gondwandaland and Laurasia which were separated by the Tethys sea. Further breakups occurred in the Jurassic, about 150 MYA and in the Cretaceous, about 65 MYA. After much more jostling and bumping the present day world was established.

An observed magnetic profile (blue) for the ocean floor across the East Pacific Rise is matched quite well by a calculated profile (red) based on the Earth's magnetic reversals for the past 4 million years and an assumed constant rate of movement of ocean floor away from a hypothetical spreading center (bottom). The remarkable similarity of these two profiles provided one of the clinching arguments in support of the seafloor spreading hypothesis.

World map showing plate boundaries (blue lines), the distribution of recent earthquakes (yellow dots) and active volcanoes (red triangles).

Volcanism at divergent and convergent plate margins.

The Mid-Atlantic Ridge,which splits nearly the entire Atlantic Ocean north to south, is probably the best-known and most-studied example of a divergent-plate boundary.

(Illustration adaptedfrom the map This Dynamic Planet.)

Here is a wonderful web site about plate tectonics by Authors: W.Jacquelyne Kious and Robert I. Tilling of the USGS.The book is a great buy!!

http://pubs.usgs.gov/gip/dynamic/dynamic.html

				Iceland is a great example of diverging plates To Iceland from Plate Tectonics Go to science-is-exciting From Plate Tectonics