Geography Reference
In-Depth Information
The Major Crustal Plates and Where They Are Going
African plate: heading southwest, away from Europe
Arabian plate: moving north toward Eurasia
Eurasian plate: moving toward the southeast
Australian plate: heading due north
Pacific plate: moving generally to the northwest
North American plate: sliding west toward the Pacific and edging south
South American plate: heading west
Back to Wegener's Pangaea, or supercontinent. The best thinking says that all the earth's land masses
were concentrated in one great mass some 220 million years ago. As the plates moved apart, Pangaea was
split into two huge continental masses. Laurasia, in the Northern Hemisphere, was made up of what be-
came North America, Europe, Greenland, and Asia. In the Southern Hemisphere, the second supercontin-
ent was Gondwanaland, made up of the future Africa, South America, Antarctica, and Australia. Other sci-
entists suggest that the process may have started out with the two smaller masses crashing together around
300 million years ago to form Pangaea, which then later reseparated. But either way, by 100 million years
ago, the current continents were taking shape. Europe broke off from North America to join with Asia,
and South America was breaking off from Africa. Then, 65 million years ago, India broke off from Africa
and moved north on a collision course with Asia. Australia, severed from Antarctica, moved to its present
position.
Is the Earth's Crust Well Done?
In a word, no. The pie is definitely still in the oven. And it will never be done.
Constantly realigning and recycling itself, the Earth is in a constant state of change. Most of the time,
these changes are imperceptible. But then San Francisco's Candlestick Park starts to rock and roll during
the middle of the 1989 World Series and everyone is reminded that Mother Nature has her own agenda.
We realize terra firma can be more terror than firma!
More extraordinary images of the changing earth have come recently in pictures from Hawaii and the
Philippines, where volcano activity has been dramatic and destructive. Yet while molten lava has flowed
down and destroyed plenty of expensive homes, it has also poured into the sea and quickly hardened,
adding inches to the coastline and sometimes creating new Hawaiian beaches instantly, which might
someday fetch a pretty penny in the real estate market. The trick is managing to stay around long enough
to capitalize.
Changes other than the sudden cataclysm of earthquakes and volcanoes are less visibly apparent. We
can't see videotape on the evening news of the ongoing process of destruction and creation happening be-
neath the earth's surface, for instance. Eventually, the changes produced by plate tectonics will be more
radical because the continents are still on the move, continuing their leisurely voyage across the mantle of
the earth. There are several ways in which the moving plates continue to shape the earth, all of them taking
place at spots called plate boundaries, where plates come together. There are three kinds of boundaries. At
neutral
, or
transform
, boundaries, plates rub against each other as they laterally move past each other. The
