Deadly and Yet Necessary ，Quakes Renew the Planet
The advantages began billions of years ago, when this crustal recycling made the oceans and atmosphere and formed the continents. Today, it builds mountains, enriches soils, regulates the planet's temperature, concentrates gold and other rare metals and maintains the sea's chemical balance.
Plate tectonics (after the Greek word "tekton," or builder) describes the geology. The tragic downside is that waves of quakes and volcanic eruptions along plate boundaries can devastate human populations.
"It's hard to find something uplifting about 150,000 lives being lost," said Dr. Donald J. DePaolo, a geochemist at the University of California, Berkeley. "But the type of geological process that caused the earthquake and the tsunami is an essential characteristic of the earth. As far as we know, it doesn't occur on any other planetary body and has something very directly to do with the fact that the earth is a habitable planet."
Many biologists believe that the process may have even given birth to life itself.
The main benefits of plate tectonics accumulate slowly and globally over the ages. In contrast, its local upheavals can produce regional catastrophes, as the recent Indian Ocean quake made clear.
Plate tectonics holds that the earth's surface is made up of a dozen or so big crustal slabs that float on a sea of melted rock. Over ages, this churning sea moves the plates as well as their superimposed continents and ocean basins, tearing them apart and rearranging them like pieces of a puzzle.
The process starts as volcanic gashes spew hot rock that spreads out across the seabed. Eventually, hundreds or thousands of miles away, the cooling slab collides with other plates and sinks beneath them, plunging back into the hot earth.
The colliding plates grind past one another about as fast as fingernails grow and over time produce mountains and swarms of earthquakes as frictional stresses build and release. Meanwhile, parts of the descending plate melt and rise to form volcanoes on land.
The recent cataclysm began in a similar manner as volcanic gashes in the western depths of the Indian Ocean belched molten rock to form the India plate. Its collision with the Burma plate created the volcanoes of Sumatra as well thousands of earthquakes, including the magnitude 9.0 killer.
《高级英语读写译教程（教师用书）》 张敬源，赵纬 主编
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