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"The Mountains Of Saint Francis" - Italy's Geologic History


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Author Topic: "The Mountains Of Saint Francis" - Italy's Geologic History  (Read 59 times)
Bianca
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« on: January 09, 2009, 09:00:55 am »


















"Italy has a highly varied landscape: old volcanoes around Rome and Naples; mountains made of limestone in the Apennines, and over near Pisa, a mountain made of pure white marble, the marble Michelangelo used for his statuary," Alvarez said. "And up in the Alps, there are great peaks of granite and metamorphic rocks and dolomite. Mountains made of sandstone and a huge volcano in Sicily at Etna. The island of Sardinia is largely made out of granite. There are other places that have an equal variety of geology, but I can't think of any that have more variety."

Starting with more recent geologic history - eruptions along a volcanic chain north of Rome over the past million years - Alvarez then takes readers back 100 million years to a time when much of Italy was an ocean floor, before it was pushed above sea level and crinkled into the rows of mountains known as the Apennines. The layered ocean-floor sediments are now visible as limestone and sandstone across the entire Apennines, folded and overthrown as the mountains were thrust up and then eroded to create a puzzle still being pieced together.

"The beautiful thing about these rocks in Italy was they were too deep to be affected by waves and storms, so they just had the most wonderful record of Earth history that you could imagine," he said.

Much of this geologic history is visible in Alvarez's favorite haunts - the quarries sprinkled throughout Italy. The quarried limestone has been used to build Italian cities since the time of ancient Rome.

"If you travel around in Italy and look at the buildings, you will see that the Italians just love ornamental stone," Alvarez said. "Even if you wander around San Francisco and look at the storefronts, you will see limestone and marble from all over Italy, as well as granites and schists."

Alvarez's own research, in particular the work in collaboration with Bill Lowrie using magnetic signatures left in sediments to date rocks, has helped reconstruct some of this Italian history.

After the Apennines appeared about 40 million years ago, in the Eocene, the continental plate known as Adria, which carried the mountain chain, collided with the European continent, shoving an even more ancient sea floor several miles up to form the Alps. Alvarez's research has helped validate the theory behind this - plate tectonics - which holds that the surface of the Earth is covered by a jigsaw puzzle of continental and oceanic plates that move around, generating mountains where they collide.

Alvarez acknowledges that most people overlook rocks in favor of ever-changing trees, flowers and wildlife, but the unchanging nature of rocks is what drew him into geology.
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