Geology Reference
In-Depth Information
ment. But as the Sun continues to warm and more water vapor enters the atmosphere, hy-
drogen will be lost to space at ever-increasing rates, slowly drying out the planet. By the
time all the oceans are dry, perhaps two billion years hence, Earth's surface will be barren
and baked; life will be on the precipice.
Novopangaea or Amasia: 250 Million Years from Now
Earth's demise is inevitable, but it's a very, very, very long way away. Projections into
the less remote future paint a more benign picture of a dynamic yet relatively safe planet.
Looking forward a few hundred million years, the past is indeed the key to understanding
the future.
Plate tectonics will continue to play a central role in changing Earth. Today the contin-
ents are scattered. Wide oceans now separate the Americas, Eurasia and Africa, Australia,
and Antarctica from one another. But these landmasses are constantly in motion, at rates of
roughly an inch or two per year—a thousand miles every 60 million years. We can estab-
lish rather precise vectors for every landmass by studying the ages of ocean-floor basalts.
Basalt near the midocean ridges is quite young, just a few million years at most. By con-
trast, basalt at continental margins and subduction zones may be more than 200 million
yearsold.It'safairlysimplemattertotakealltheseocean-floorages,playtheplatetecton-
ics tape backward in time, and obtain a glimpse of Earth's shifting continental geography
during the past 200 million years. From that information, it may also be possible to project
plausible plate motions more than 100 million years into the future.
Given their present trajectories across the globe, it appears that all the continents are
headed for another collision. A quarter-billion years from now (more or less), most of
Earth'slandwillagainformonegiantsupercontinent—alandalreadynamedNovopangaea
bysomeprescientgeologists.However,theexactarrangementofthatfutureisstillamatter
of debate.
Assembling Novopangaea is a tricky game. It's easy to take today's continental move-
ments and predict ten or twenty million years down the road. The Atlantic will have
widened by several hundred miles, while the Pacific will have shrunk by an equal amount.
Australia will have moved north toward South Asia, and Antarctica will have shifted
slightly away from the South Pole, also in the direction of South Asia. Africa is also on the
move, inching northward to close off the Mediterranean Sea. In a few tens of millions of
years, Africa will have collided with southern Europe, in the process closing up the Medi-
terraneanandpushingupaHimalayan-sizemountainrangethatwilldwarftheAlps.Sothe
map of the world twenty million years hence will appear familiar but skewed. Looking as
farasonehundredmillionyearsintothefutureinthiswayisfairlysafe,andmostmodelers
