ancy uplifted the Himalaya Mountains and the broad Tibetan Plateau (Fig.
186), the size of which has not been equaled on this planet for more than 1
billion years.
During the past 5 to 10 million years, the entire region rose over a mile
in elevation.The continental collision heated vast amounts of carbonate rock,
spewing several hundred trillion tons of carbon dioxide into the atmosphere.
This might explain why Earth grew so warm during the Eocene epoch from
54 million to 37 million years ago, when temperatures reached the highest of
the past 65 million years. According to the fossil record, winters were warm
enough for crocodiles to roam as far north as Wyoming, and forests of palms,
cycads,and ferns covered Montana.
About 50 million years ago, the Tethys Sea separating Eurasia from Africa
narrowed as the two continents approached each other, then began to close
off entirely some 20 million years ago. Thick sediments that had been accu-
mulating for tens of millions of years buckled into long belts of mountainFigure 185The south
side of Mount Adams,
with Mount Rainer in the
background, Cascade
Range,Yakima, County
Washington.
(Photo by A. Post, courtesy
USGS)
Historical Geology