Scott Parker, age 12, of P"uncie, Indiana, for his question:
What made the Appalachian Mountains?
The northern arm of the Appalachians was made about 300 million years ago and the southern arm arose about 100 million years later. The layers of faulted and folded rocks reveal when the massive mountain chain was built and also part of the story of how it was built. The answers to what made it are deep below the rocky surface crust. In the past few years, earth scientists have found evidence that mountain making may be linked to a lot of other stupendous geographical happenings.
The term for mountain making is "diastrophism", which means deforming the earth's crust. The term "isostasy", meaning "equally balanced", suggests why and how these massive crustal ridges are pushed up, cracked and stacked like multiple rocky sandwiches. It seems that the global crust strives to keep its weight evenly distributed. Countless tons of surface debris constantly are shifted by the erosion of the weather and running water. When these heavy deposits accumulate in enormous trenches, mountains arise to adjust the crustal weight.
The northern arm of the Appalachians stretches from Newfoundland to Virginia. Some 400 million years ago, this enormous arm was a geosyncline a long, deep trench fed by silty streams. Through the ages, the streams dumped gravels and sandy clays into the huge ditch and marine creatures of the Paleozoic Era left their fossils in its muddy floor. Ages later, the clogging geosyncline became a soggy swamp. Scrawny coal forests grew there, sharing the steamy air with giant dragonflies while whopping salamanders wallowed in the mud.
About 300 million years ago, the accumulated deposits became critical and isostasy began adjusting the weight of the old geosyncline. The massive crust arose in more or less parallel ridges, generating enormous heat and pressure deep below the surface. Volcanos erupted igneous lava, earthquakes helped to crack and. stack the deformed crustal blocks in ragged ranges of young mountains. The stupendous project took many millions of years.
Meantime, another geosyncline was filling with silty desposits. About 200 million years ago, its weight became critical and the southern arm of the Appalachians began to arise. Its younger ranges nova reach southward from the northern arm as far as Alabama, making the entire Appalachian chain about 1,500 miles long. Time and weather have rounded and eroded the ragged crests. And during, the ice ages, the ranges as far south as New York were scarred and denuded by glaciers.
Nowadays, scientists favor a global view of the restless earth. They see the Appalachians and other enormous ranges as local features related to somewhat mysterious planetary forces. They have just about enough evidence to prove that the drifting continents have been inching apart through the ages. The magnetic poles and even the geographic poles also are shifting. There is evidence that these mysterious global activities helped to build the high Himalayas. Possibly they also operated behind the scenes when the Appalachians were made.