Lori Rich, age 10, of Bridgeport, Connecticut, for her question:
How did the earth form Grand Canyon?
Some people still call it The Grand Canyon. Others call it Grand Canyon, perhaps to match Bryce Canyon and various other canyons named for persons or places. Actually it is an enormous ditch in the earth's crust. But no other canyon can compare with its majestic grandeur, with its expanse of wind carved rocks and the rainbow colors that change with every shimmering sunbeam and passing cloud.
Every season, millions of awe struck visitors stand beside Grand Canyon and gape across eight miles to the rim on the other side. The sides of the enormous ditch dip down a mile, in a series of picturebook terraces. Down there at the bottom is a shiny, brownish colored ribbon of running water. This happens to be the mighty Colorado River, the industrious digger that scooped the enormous canyon in the earth.
About 600 million years ago, the earth began covering this region with layers of sedimentary sandstones and limestones and various other rocky. layers. Some ten million years ago, the rocky sandwich was 12,000 feet thick and the great slab began to rise and rise, way above sea level. As the landscape tilted, no doubt many local streams changed their courses and took the easy routes down the slopes. But for reasons unknown, the Colorado River refused to be rousted from its channel. As the land rose on either side, its swift current carried away the dirt and dug down deeper, deeper and still deeper.
After some 10 million years of toil, this amazing river gouged out Grand Canyon, 217 miles long and about one mile deep. Meantime, winds and weather had been working to erode the steep canyon walls, exposing; ledges of ancient rocks that step down to the river in a series of terraces. Landslides fanned down from the rims and windblown sand eroded fantastic carvings on the countless cliffs.
The rushing river still dashes along, carrying an estimated 500,000 tons of dirt from the bottom of the canyon every day. Every 2,000 years or so, it digs its channel about one foot deeper. Its strong current can split a six food boulder and mash it to mud in about four yea's, Earth scientists expect it to continue its vigorous digging for centuries to come.
But, eventually, our geographical hero will become choked by debris. Then erosion will try to fill the bid ditch, move back its rims and reduce them to bluffs. The aged river is expected to spend a peaceful old age, lazily ambling from side to side.
To visitors, Grand Canyon is a sight too stupendous to be captured on film. Nature lovers are fascinated by numerous plants and animals that share separate ecologies on the different terraces. Geologists are overwhelmed to explore ledges of exposed rocks that date back layer by layer through more than half a billion years.