Something dramatic happened about 500 million years ago called the Cambrian "explosion," during which an incredible diversity ...

The age of the fossil must be determined so ... it is possible to work out the relative ages of rocks. In the Grand Canyon, the layers of strata are nearly horizontal. Most sediment is either ...

This story appears in the February 2012 issue of National Geographic magazine. Carry a lawn chair and a sunshade—plenty of water too—onto the sage flats just south of Arizona's Highway 89A ...

The Grand Canyon was carved out of rock by the Colorado River over millions ... but changed due to rising sea-levels following the Ice Age. How has glaciation shaped the landforms of the Northern ...