How old is the Grand Canyon? Scientists haves been working on the answer for decades. Some believe the canyon is fairly young, in geologic terms, having been carved out by the Colorado River in the past five millions years (give or take a few years). Other researchers believe the canyon is much older, maybe by ten times that much. According to the latest discoveries, the answer seems to depend on how you define “the Grand Canyon,” because different parts show a different history.
To help estimate ancient erosion rates, the team turned to thermochronology—the study of how a rock's temperature has changed through its history. Because temperature rises as depth in the Earth's crust increases, a rock's thermal history provides insight into when, and how quickly, terrain above it eroded away.
In the new study, the researchers used a variety of techniques to analyze samples of phosphate-bearing rocks taken from four of the five major sections of the canyon, both from river level and from the canyon rim, which typically lies almost a mile (1.5 kilometers) above the river.
The techniques used to date the canyon are a bit complicated, but you can read about them at National Geographic News. The conclusions of this latest research reveal that the area had several canyons in the distant past, with now-extinct rivers. Then they were joined together by events that happened 25 million years ago and then again at about five or six million years ago, when the Colorado River was formed. After all, when you’re that big and that old, you are bound to have a complicated history. -via the Presurfer
(Image credit: Erik Harrison)