An aerial picture of the Grand Canyon in Arizona taken on July 1, 2013 from around 30,000 feet (10,000m). The Grand Canyon, considered one of the seven natural wonders of the world, is 277 miles (446 km) long, up to 18 miles (29 km) wide and attains a depth of over a mile (1.8km). Nearly two billion years of the Earth's geological history has been exposed as the Colorado River and its tributaries cut their channels through layer after layer of rock while the Colorado Plateau was uplifted. While the specific geologic processes and timing that formed the Grand Canyon are the subject of debate by geologists, recent evidence suggests the Colorado River established its course through the canyon at least 17 million years ago. Since that time, the Colorado River continued to erode and form the canyon to its present-day configuration. AFP PHOTO/JOE KLAMAR (Photo credit should read JOE KLAMAR/AFP/Getty Images)
