When you look at a map of the world, it seems as though it was always like that - North America on top of South America, Europe north of Africa, Australia off at the bottom right. But really all of the dry land on Earth moves around like islands about 60 miles thick on top of hot, mushy rock in the mantle - the hotter part of the Earth between us and the Earth's iron core. Land masses move around the way bath toys move around in the bathtub. Probably this happens on some other planets, too. The land masses move very slowly - usually no more than twenty centimeters in a year.
Watch the continents float around!
Like the bath toys, sometimes the land masses are all clumped together in one part of the Earth, and other times they drift apart. This has happened at least three times since the dry land masses first appeared on Earth about four billion years ago. When the land masses run into each other, or slide under each other, it causes earthquakes and volcanoes, and sometimes huge mountain chains, like the Alps or the Himalayas, get pushed up high above sea level.
Just over a billion years ago, all the land clumped together in one big land mass we call Rodinia. At this time there were only simple sea plants on Earth, and nothing much lived on land. Rodinia broke apart eventually, and then in the time of the first spiders and insects the land came back together again in another big clump we call Pannotia, about 500 million years ago, and then moved apart again.
The most recent time that the land masses all clumped together was about 250 million years ago, during the time of the dinosaurs. We call this super-continent Pangaea (pan-JAY-ah). Then, about 180 million years ago, the land masses began to drift apart again, and they are still drifting away from each other today.
First Pangaea broke in half into two pieces, Laurasia and Gondwana. Then Laurasia broke up into North America, Europe and Asia. Gondwana broke up into South America, Africa, Antartica, and Australia. If you look at the continents today, you can see how South America would have fit against Africa.
The land masses are still moving today. North America and South America are gradually moving away from Europe and Africa, so that the Atlantic Ocean is getting bigger and the Pacific Ocean is getting smaller. The California edge of the Pacific Ocean is ramming into North America and sliding past it, causing earthquakes in California and forming the Rocky Mountains. In several hundred million years, the Pacific Ocean will disappear, and the West Coast of North America will smash into Japan and China, forming another large land mass, and probably another large mountain range.
To find out more about plate tectonics, check out these books from Amazon.com or from your library:
MARTIN L. KING JR.
BILL OF RIGHTS
BILL OF RIGHTS
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