ICE AGES

The image below is a photo of the exhibit panel. Following it is a transcript of the panel.

Photo of the panel from the exhibit.

Vast sheets of ice repeatedly covered the northern continents during the Age of Mammals.

There may have been 21 separate glacial episodes during the Age of Mammals. Of these, the four major events occurred:

  • 1.6 to 1.3 million years ago
  • 1 million to 700 thousand years ago
  • 550 to 400 thousand years ago
  • 70 to 12 thousand years ago

Chilling Out
A major glaciation removes water from the oceans and lowers sea levels worldwide. As colder climates spread in the Northern Hemisphere, temperate and tropical climate zones are pushed southward. Plants and animals must adapt, or alter their ranges, in order to survive.

Bay Area Brrrrrr!
There hasn't always been a bay in the San Francisco Bay Area. Our bay formed after the last glaciation (about 12 thousand years ago) as melting water filled what was then a river valley. During maximum glaciation, our shoreline began where the Farallon Islands are today!

Glacier-smoothed stones show up in the strangest places. Moving glaciers carry with them rocks picked up along the way. As glaciers melt, such rocks -- now smoothed or polished -- are deposited far from their original source. These rocks, probably from north woods of central Canada, were collected on the plains of eastern Montana.

PICTURE CAPTIONS:

  • maximum glaciation -- 20 thousand years ago
  • present day glaciation
  • rocks smoothed and polished by glacial action between 70,000 and 15,000 years ago; Montana


NOTE: This panel describes rocks from Eastern Montana. Those rocks were part of an exhibit originally installed at the California Academy of Sciences. The samples are not present here at CCSF.