Long-Term Global Forecast? Fewer Continents
By WILLIAM J. BROAD
Published: January 9, 2007
Kiss the Mediterranean goodbye. Ditto the Red Sea and its wonderland of coral reefs and exotic sea life. And prepare for the day when San Francisco has a gritty new suburb: Los Angeles. Indeed, much of Southern California, including the Baja Peninsula, will eventually migrate up the west coast to make Alaska even more gargantuan.
Scientists predict that in 25 million years, The Gulf of California will widen into a narrow seaway.
Geologists have long prided themselves on their ability to peer into the distant past and discern the slow movements of land and sea that have continuously revised the planet’s face over eons. Now, drawing on new insights, theories, measurements and technologies — and perhaps a bit of scientific bravado — they are forecasting the shape of terra firma in the distant future.
The maps and animations by these scientists are helping explain core principles of geology to increasingly wide audiences. Schools, textbooks, museums, Web sites and television shows now routinely feature images of what the forecasters say the planet will look like eons from now. And geologists are using the forecasts to deepen their own investigations of plate tectonics.
“It’s tremendous,” said Warren J. Nokleberg, a senior research geologist at the United States Geological Survey in Menlo Park, Calif. “It lets students and scientists better appreciate the mobile Earth, to see where it’s going. That’s very powerful.”
Practitioners acknowledge that their predictions, however intriguing, become more theoretical when pushed far into the future, as with advanced weather forecasts. Their most ambitious efforts peer 250 million years ahead. But their more short-term predictions, they note, draw on mountains of geophysical data and involve relatively small extrapolations of current trends, like the steady northward march of Southern California.
Despite uncertainties, the field of geopredictions is booming. One Web site has received almost 30 million hits since its debut in 1998, and the field’s admirers now include top scientists.
“It’s quite good pedagogically,” said Frank Press, a geologist and past president of the National Academy of Sciences. “It captures the attention.”
Dr. Press features one of the forecasts in his introductory college text, “Understanding Earth” (Freeman, 2006). He and three co-authors present a snapshot of how the planet’s surface might look 50 million years from now, calling it “a plausible scenario.”
Among other things, the snapshot shows that Africa has drifted to the north, plowing into Europe and fusing the two landmasses, eliminating the Mediterranean Sea and replacing it with the Mediterranean Mountains. The rugged range runs down the middle of a continent far bigger than current-day Eurasia, a giant new agglomeration that might be called Afrasia.
While peering 50 million years into the future may seem like a stretch, geologists consider such spans of time the blink of an eye. If one year represented Earth’s past, 50 million years would equal less than 4 days, or about the limit of accurate weather forecasts.
“Fifty million is fairly straightforward,” said Christopher R. Scotese, a geologist at the University of Texas, Arlington, who has pioneered the predictions in recent years. “It’s like you’re driving on the highway and you want to know where you’re going to be in 10 minutes. You check the speedometer, do a calculation, and project your present motion.
“But beyond 50 million years,” Dr. Scotese added, “like on the highway, unexpected things can happen.”
Forecasts of future continental motion developed slowly as offshoots of the theory of plate tectonics, which won acceptance in the 1960s and 1970s, shattering old dogmas of continental immobility. The theory of plate tectonics holds that the surface of Earth is composed of a dozen or so huge crustal slabs that float on a sea of partially molten rock. Over ages, hot convection currents in this sea, as well as gravitational forces, move the plates and their superimposed continents and ocean basins, tearing them apart and rearranging them like pieces of a giant jigsaw puzzle.
The theory, named for the Greek word “tekton,” or builder, is a study in slowness. Colliding plates grind past one another about as fast as fingernails grow.
Today, geologists measure such changes with great precision thanks to the advent of global positioning satellites and small base stations that dot remote areas of the planet and operate unattended. Arrays of such instruments track the overall movement of plates.
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