Posted on 04/26/2008 3:20:58 PM PDT by blam
Sierra Nevada Rose To Current Height Earlier Than Thought, Say Geologists
Geologists studying deposits of volcanic glass in the western United States have found that the central Sierra Nevada largely attained its present elevation 12 million years ago, roughly 8 or 9 million years earlier than commonly thought. (Credit: iStockphoto/Ken Babione)
ScienceDaily (Apr. 26, 2008) — Geologists studying deposits of volcanic glass in the western United States have found that the central Sierra Nevada largely attained its present elevation 12 million years ago, roughly 8 or 9 million years earlier than commonly thought.
The finding has implications not only for understanding the geologic history of the mountain range but for modeling ancient global climates.
"All the global climate models that are currently being used strongly rely on knowing the topography of the Earth," said Andreas Mulch, who was a postdoctoral scholar at Stanford when he conducted the research. He is the lead author of a paper published recently in the online Early Edition of the Proceedings of the National Academy of Sciences.
A variety of studies over the last five years have shown that the presence of the Sierra Nevada and Rocky Mountains in the western United States has direct implications for climate patterns extending into Europe, Mulch said.
"If we did not have these mountains, we would completely change the climate on the North American continent, and even change mean annual temperatures in central Europe," he said. "That's why we need to have some idea of how mountains were distributed over planet Earth in order to run past climate models reliably." Mulch is now a professor of tectonics and climate at the University of Hannover in Germany.
Mulch and his colleagues, including Page Chamberlain, a Stanford professor of environmental earth system science, reached their conclusion about the timing of the uplift of the Sierra Nevada by analyzing hydrogen isotopes in water incorporated into volcanic glass.
They analyzed volcanic glass at sites from the Coast Ranges bordering the Pacific Ocean, across the Central Valley and the Sierra Nevada and into the Basin and Range region of Nevada and Utah.
The ratio of hydrogen isotopes in the glass reflects changes that occurred to the water vapor content of air over the Pacific Ocean as it blew onto the continent and crossed the Sierra Nevada. As the air gains elevation, it cools, moisture concentrates and condenses, and it rains. Water containing heavier isotopes of hydrogen tends to fall first, resulting in a systematic decrease in the ratio of heavy water molecules to lighter ones in the remaining water vapor.
Because so much of the airborne moisture falls as rain on the windward side of the mountains, land on the leeward side gets far less rain—an effect called a "rain shadow"—which often produces a desert.
The higher the mountain, the more pronounced the rain shadow effect is and the greater the decrease in the number of heavy hydrogen isotopes in the water that makes it across the mountains and falls on the leeward side of the range. By determining the ratio of heavier to lighter hydrogen isotopes preserved in volcanic glass and comparing it with today's topography and rainwater, researchers can estimate the elevation of the mountains at the time the ancient water crossed them.
Volcanic glass is an excellent material for preserving ancient rainfall. The glass forms during explosive eruptions, when tiny particles of molten rock are ejected into the air. "These glasses were little melt particles, and they cooled so rapidly when they were blown into the atmosphere that they just froze, basically," Mulch said. "They couldn't crystallize and form minerals."
Because glass has an amorphous structure, as opposed to the ordered crystalline structure of minerals, there are structural vacancies in the glass into which water can diffuse. Once the glass has been deposited on the surface of the Earth, rainwater, runoff and near-surface groundwater are all available to interact with it. Mulch said the diffusion process continues until the glass is effectively saturated with water.
Other researchers have shown that once such volcanic glass is fully hydrated, the water in it does not undergo any significant isotopic exchange with its environment. Thus, the trapped water becomes a reliable record of the isotopic composition of the water in the environment at the time the glass was deposited.
"It takes probably a hundred to a thousand years or so for these glasses to fully hydrate," Mulch said. But 1,000 years is the blink of an eye in geologic time and, for purposes of estimating the timing of events that occur on scales of millions or tens of millions of years, that degree of resolution is quite sufficient.
Likewise, you need deposits of volcanic ash that were laid down relatively quickly over a broad area. But that's the norm for explosive eruptions. Though some ash may circulate in the upper atmosphere for a few years after a major eruption, significant quantities are generally deposited over vast areas within days.
The samples they studied ranged from slightly more than 12 million years old to as young as 600,000 years old, a time span when volcanism was rampant in the western United States owing to the ongoing subduction of the Pacific plate under the continental crust of the North American plate.
"As we use these ashes that are present on either side of the mountain range, we can directly compare what the water looked like before and after it had to cross this barrier to atmospheric flow," Mulch said. "If you just stay behind the mountain range, you see the effect of the rain shadow, but you have to make inferences about where the water vapor is coming from, what happened to the clouds before they traveled across the mountain range.
"For the first time, we were able to document that we can track the [development of the] rain shadow on both sides of the mountain range over very long time scales."
Until now, researchers have been guided largely by "very good geophysical evidence" indicating that the range reached its present elevation approximately 3 or 4 million years ago, owing to major changes in the subsurface structure of the mountains, Mulch said.
"There was a very dense root of the Sierra Nevada, rock material that became so dense that it actually detached and sank down into the Earth's mantle, just because of density differences," Mulch said. "If you remove a very heavy weight at the base of something, the surface will rebound."
The rebound of the range after losing such a massive amount of material should have been substantial. But, Mulch said, "We do not observe any change in the surface elevation of the Sierra Nevada at that time, and that's what we were trying to test in this model."
However, Mulch said he does not think his results refute the geophysical evidence. It could be that the Sierra Nevada did not evolve uniformly along its 400-mile length, he said. The geophysical data indicating the loss of the crustal root is from the southern Sierra Nevada; Mulch's study focused more on the northern and central part of the range. In the southern Sierra Nevada, the weather patterns are different, and the rain shadow effect that Mulch's approach hinges on is less pronounced.
"That's why it's important to have information that's coming from deeper parts of the Earth's crust and from the surface and try to correlate these two," Mulch said. To really understand periods in the Earth's past where climate conditions were markedly different from today, he said, "you need to have integrated studies."
The research was funded by the National Science Foundation.
Adapted from materials provided by Stanford University.
RightWhale answered:
That would be 350 million minus 2000 or 349,997,000 BC
Wrong, Whale, 350 million minus 2000 is NOT 349,997,000.
Geology is barely a science. Mostly opinions, like psychology.
If it has math it is natural science.
Wrong again, Whale, geology is very much a natural science.
Indeed. Around 1650, Archbishop James Ussher of the Church of Ireland calculated that the earth was created on October 23, 4004 BC at 9:00 AM, Pacific Daylight Time.
On October 23, 1972, at 9 in the morning, the Geology Department at Occidental College threw a birthday party for the earth which made the evening news.
Fields or related disciplines
Earth science
Economic geology
Mining geology
Petroleum geology
Engineering geology
Environmental geology
Geoarchaeology
Geochemistry
Biogeochemistry
Isotope geochemistry
Geochronology
Geodetics
Geography
Geological modelling
Geomicrobiology
Geomorphology
Geomythology
Geophysics
Glaciology
Historical geology
Hydrogeology or geohydrology
Mineralogy
Oceanography
Marine geology
Paleoclimatology
Paleontology
Micropaleontology
Palynology
Petrology
Petrophysics
Plate tectonics
Sedimentology
Seismology
Soil science
Pedology (soil study)
Speleology
Stratigraphy
Biostratigraphy
Chronostratigraphy
Lithostratigraphy
Structural geology
Volcanology
http://en.wikipedia.org/wiki/Geology#Fields_or_related_disciplines
Vladimir Lenin
Владимир Ильич Ленин
Chairman of the Council of People’s Commissars
In office: November 8, 1917 – January 21, 1924
Born April 22, 1870
Died January 21, 1924
Political party Bolshevik Party
Profession Politician, revolutionary
". . . on April 22, 1970, Earth Day was held, one of the most remarkable happenings in the history of democracy. . . "
--American Heritage Magazine, October 1993
Founded on Lenin's 100th birthday? --yeah, it's a "coincidence". LOL.
Earth Day 1970 (the very first Earth Day):
"The nationwide event included opposition to the Vietnam War on the agenda, but this was thought to detract for the environmental message.
Pete Seeger was a keynote speaker and performer at the event held in Washington DC."
http://en.wikipedia.org/wiki/Earth_Day#Earth_Day_1970
From David Horowitz's FrontPageMag.com/DiscoverTheNetwork.org:
Profile: PETE SEEGER
*Musician, folksinger, songwriter, and political activist
*Joined the Communist Party in 1942
*"I'm still a Communist" -- Pete Seeger, 2004
http://www.discoverthenetworks.org/individualProfile.asp?indid=1619
Also see:
America’s Most Successful Communist [Pete Seeger]
by Howard Husock
"The Popular Front sought to enlist Western artists and intellectuals, some of them not party members but 'fellow travelers,' to use art, literature, and music to insinuate the Marxist worldview into the broader culture. The murals of Diego Rivera, the poetry of Langston Hughes, the novels of Howard Fast—all exemplified this approach. It’s an irony that communists should seek to change the culture, of course, since Marxism holds that culture is merely a reflection of underlying economic structures, whose transformation will bring about capitalism’s inevitable collapse."
http://www.city-journal.org/html/15_3_urbanities-communist.html
“Geology is barely a science. Mostly opinions, like psychology.”
As a former geologists, my view is that geology is more like story-telling as we make up explanations for what we see.
Can the same be said for chemistry, physics, biology, and astronomy?
Indeed, on the first "Earth Day" in 1970, Lenin's picture was posted on the Freeman Union at Occidental College, where I was an undergraduate.
"As a former geologists", eh?
Explain in your own words the difference between igneous rock and metamorphic rock.
And he was born on April 22, 1870. So the very first Earth Day just happened to be Lenin's 100th birthday. What a remarkable coincidence! :)
Thanks for the advice. There would be no charge I assume.
Seismology uses lots of math, even tensors, sat in math class with some of these scientists. Climatology uses lots of math. These might be natural sciences. You know more about geology than I do. How did the moon come to be, oh, mighty geologist?
I’m not a geologist. You’re not a geologist. Thermodynamics is not geology. Seismology is not geology. Tectonics is all opinion. Computer modeling is not science. Field trips are not science. How did the moon come to be?
Yes.
First of all, where did you get the idea that using math establishes a science as a "natural science"? Perhaps you're confusing the distinctions between the physical sciences and the life sciences? But even in that case, I don't think the use (or non-use) of mathematics makes any difference. Then there's also the 'hard sciences'. Anyway, many, if not most, fields of geology involve mathematical calculations. Mineralogy, structural geology, paleogeography, plate tectonics, geomorphology, geophysics, etc, all are very high tech relying heavily on complex calculations and computer analysis.
How did the moon come to be?
The Moon is now thought to have been formed as a result of an ancient collision between a rogue Mars-sized planet and the proto Earth. The Moon, they think, is made up of material ejected from the collision and then pulled into a sphere by gravity.
BTW: I'm not a geologist. But I used to be a geo major some years back. (during the end of the last ice age)
The moon stories are all opinion, every last one of them. As far as computer analysis, most of it is none other than aristotelian logic, which is a way of saying that the conclusion is already present in the premise and is merely being exposed for the slow of thought: nothing new comes from that. Math is the only object that is not internally subject to opinion, is true, period.
One of the things that most attracted me to geology was the fact that it was basically a combination of all the sciences. I originally was a physics major but fell in love with nature while on some camping trips in the Catskill Mountains of Upstate New York. I found that within geology, areas such as earth history/plate tectonics, the formation of landforms, physics, chemistry, biology and paleontology, were all parts under one umbrella. Much more interesting and satisfying.
One of the main USGS earthquake facilities is just up the road. Heavy math happens there, including tensor math. Went to school with a couple of their programmers; they did okay in real analysis and complex analysis. I might have gone on to post grad mathematical physics but decided to retire instead. Science is a young man’s game.
Well then you'd better hope their math is better than yours!
Re: That would be 350 million minus 2000 or 349,997,000 BC
:) (everyone makes these sorts of mistakes. i certainly do)
It’s not. They had to work hard to keep up. There were some foreign students in the class that one would have to admit were ahead of all of us, but we gave them a fair run.
Astrology also uses math. Does that make it a "natural" science?
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