Page 36 - Curriculum Visions Dynamic Book

Continental drift
The process of crustal movement has been going on for at least three billion years. Evidence that it happens (geologically speaking) quickly is that there is no rock on the ocean floors older than about 200 million years.
Going back in time before three billion years, we also see
a world in which convection was even more powerful, when the crust was only just solidifying, and when collisions between the Earth and other space bodies were more frequent and more damaging. The development of large plates that moved, undisturbed by giant impacts from space, had to wait for nearly a billion years of the Earth’s development.
When it did happen, it reorganized the distribution of land and sea, of mountains and plains, of desert and tropical areas and cold poles time and time again. The maps on this page show what has happened over just the last 300 million years.
 The Earth as it looked in Carboniferous times, 300 million years ago. Notice that most of the continents are gathered around the South Pole, and that they are all joined in a supercontinent called Pangea.
convection The circulating flow in a fluid (liquid or gas) that occurs when it is heated from below.
plate A very large unbroken part of the crust of a planet. Also called tectonic plate.
Late Carboniferous 306 Ma
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Carboniferous-age desert Carboniferous-age tropical swamp
Carboniferous-age desert
Carboniferous glaciation
Key to diagrams
Ancient landmass
Modern landmass
Subduction zone (triangles point in direction of subduction)
Seafloor spreading ridge
 The Earth’s surface has been on
the move ever since the crust formed. Reconstructions of the past show a
very different planet 300 million years ago (below), 190 million years ago (opposite top), and 94 million years ago (opposite bottom). Such differences would have had major effects on the water cycle, the atmosphere, and the formation of mountains.