Much has been learned about the geology of the Grand Canyon and about the history of life on earth since Powell ... In some locations there are land plants and reptile tracks.

At the Grand Canyon, summer brings heavy traffic ... but each little oasis supports a web of complex plant and animal life. Thanks to the 6,000-foot elevation difference between the Colorado ...

The Grand Canyon may rewrite the textbooks on the Cambrian Explosion—a key turning point in Earth's history when there was a sudden boom in complex life and ... without land plants and during ...