杏吧原创

VOLCANOES triggered the deep freeze that has covered polar regions with ice
for millions of years, geologists say.

For years, researchers have debated the causes of the latest series of ice
ages, which began roughly 2.6 million years ago. Among the suspects were
periodic changes in the tilt of the Earth鈥檚 rotation axis and its orbit. Another
contender was tectonic changes. The raising of the Himalayan Plateau was among
several tectonic changes that could have altered air and water circulation,
redistributing heat around the planet.

But in this month鈥檚 Geology(vol 26, p 1027), David Rea and Libby
Prueher of the University of Michigan in Ann Arbor say that while these factors
readied the planet for glaciation, volcanic eruptions pushed the climate 鈥渙ver
the edge鈥�. Ocean cores from the North Pacific show glaciation started within
3000 years, faster than possible if the trigger was orbital or tectonic.

Ash was also in the cores. 鈥淎ll around the North Pacific, volcanoes started
firing off,鈥� says Rea. The smoke would have chilled the Earth by blocking
sunlight.