TF347-Ceology’s Impact on the Economy of the United States

• 2023-05-25 08:30:22 来源：哔哩哔哩

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Ceology’s Impact on the Economy of the United States

Geology’s Impact on the Economy of the United States The United States has benefited economically from a number of developments in its geological history.Consider first the birth of the Rocky Mountains and its effect on the biogeography of the Great Plains,which reach from the eastern edge of the Rocky Mountains in the West to the Mississippi River in the East,and which have contributed enormously to agricultural productivity.Before the creation of the mountains,a process geologists refer to as the Laramide orogeny,beginning some 80 million years ago,the region now known as the Great Plains was a tremendous inland sea.The emergence of the Rockies,however,plugged the water’s entry from the Pacific and Arctic oceans,creating conditions favorable to the eventual emergence of forest cover on the plains.The mountains also dried out the land by capturing the moisture of the clouds on their western side,creating a huge rain shadow that left the plains to the east in an even more arid state,precisely an environment suitable for the growth of grass.Meanwhile,the rain that did fall in the mountains washed away sediments and deposited them further east with each passing year,covering the old seabed with a layer of loose silt that was hundreds of feet thick and producing in the process one of the most level stretches of land on Earth.The Rockies,by drying out the landscape of the plains,encouraged the growth of grasses,which, due to complicated root systems that can exploit even the smallest amount of moisture,flourish in such an environment.Into these grasslands the American pioneer eventually forged,prepared to break the sod and replace it with another grass:the wheat so fabulously adapted to life in an arid locale.

That was not all the Laramide mountain-building episode did to contribute to America’s economic strength.It also broke up granite and metamorphic rocks,allowing metallic minerals to insinuate themselves into the faults left behind.Deposits of gold,silver,zinc, lead,and copper settled that much nearer Earth’s surface,where they could be mined with relative ease.Without this geological episode, there would have been no Colorado gold rush in the 1850s,no mineral belt running through that state.The Laramide revolution was but one geological event on the nation’s road to wealth.Taken together,the combined effect of the region’s geological history accounts for North America’s near total self-sufficiency in minerals.

Another sequence of events from the distant past is also worth our attention:the development and retreat of glaciers during the Pleistocene epoch which began about 1.6 million years ago.During this time,huge glaciers covered the northern reaches of the continent (as well as Europe and Asia).These glaciers were as much as one to two miles thick.Tundra-land that has permanently frozen subsoil and supports only low-level vegetation-stretched out over what is now Manhattan.The ice expanded south and then retreated on some 18 to 20 different occasions over the Pleistocene.The cause of the alternation between periods of glacier advance and periods of glacier retreat is not completely understood,but many attribute the shifts to periodic changes in Earth’s orbit known as the Milankovitch cycle, discovered back in the 1920s by the Yugoslav geophysicist Milutin Milankovitch.From time to time,Milankovitch observed,Earth’s orbit around the Sun changes,sometimes placing the planet closer to the star,where it can receive more heat,and sometimes farther away, making the climate colder and producing a glaciation.

Whatever the reason,beginning about 10,000 years ago,the climate shifted and the ice sheet that covered much of Canada and the northern United States withdrew.And again,United States agriculture seems to have benefited from yet another geological event.When the glaciers retreated on several occasions from the Great Plains,they left behind a fine soil deposit called loess.The loess was eventually driven east by the prevailing westerly winds, finding its way to middle American states like Kansas,Nebraska, lowa,Wisconsin,and Indiana,and providing the basis for rich,fertile soil-in some places 20 feet thick.Likewise,glaciers scraped up the soils of eastern Canada and,in a generous manner,dumped them in the Midwest,again bolstering the fertility of its farms. 

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►Geology’s Impact on the Economy of the United States The United States has benefited economically from a number of developments in its geological history.Consider first the birth of the Rocky Mountains and its effect on the biogeography of the Great Plains,which reach from the eastern edge of the Rocky Mountains in the West to the Mississippi River in the East,and which have contributed enormously to agricultural productivity.Before the creation of the mountains,a process geologists refer to as the Laramide orogeny,beginning some 80 million years ago,the region now known as the Great Plains was a tremendous inland sea.The emergence of the Rockies,however,plugged the water’s entry from the Pacific and Arctic oceans,creating conditions favorable to the eventual emergence of forest cover on the plains.The mountains also dried out the land by capturing the moisture of the clouds on their western side,creating a huge rain shadow that left the plains to the east in an even more arid state,precisely an environment suitable for the growth of grass.Meanwhile,the rain that did fall in the mountains washed away sediments and deposited them further east with each passing year,covering the old seabed with a layer of loose silt that was hundreds of feet thick and producing in the process one of the most level stretches of land on Earth.The Rockies,by drying out the landscape of the plains,encouraged the growth of grasses,which, due to complicated root systems that can exploit even the smallest amount of moisture,flourish in such an environment.Into these grasslands the American pioneer eventually forged,prepared to break the sod and replace it with another grass:the wheat so fabulously adapted to life in an arid locale. 

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