What is geology?

Part 1: Modified from "Physical Geology: Exploring the Earth, v. 4" by Monroe and Wicander

What is geology and what do geologists do? Geology, from the Greek geo and logos, is defined as the study of the Earth. It is generally divided into two broad areas-physical geology and historical geology. Physical geology is the study of Earth materials, operating as minerals and rocks, as well as the processes operating within Earth and on its surface. Historical geology examines the origin and evolution of Earth, its continents, oceans, atmosphere, and life.

Nearly every aspect of geology has some economic or environmental relevance. Many geologists are involved in exploration for mineral and energy resources, using their specialized knowledge to locate the natural resources on which our industrialized society is based. As the demand for these nonrenewable resources increases, geologists are applying the basic principles of geology in increasingly sophisticated ways to help focus their attention on areas with a high potential for economic success.

Although locating mineral and energy resources is extremely important, geologists are also being asked to use their expertise to help solve many environmental problems. Some geologists are involved in finding groundwater for ever-burgeoning needs of communities and industries or in monitoring surface and under-ground water pollution and suggesting ways to clean it up. Geologic engineers help find safe locations for dams, waste-disposal sites, and power plants and design earthquake-resistant buildings.

Geologists are also involved in making short- and long-range predictions about earthquakes and volcanic eruptions and the potential destruction that may result. In addition, they are working with civil defense planners to help draw up contingency plans should such natural disasters occur.

As this brief survey illustrates, geologists follow a wide variety of pursuits. As the world's population increases and greater demands are made on Earth's limited resources, the need for geologists and their expertise will become even greater.

Destructive volcanic eruptions, devastating earthquakes, disastrous landslides, large sea waves, floods, and droughts make headlines because they wreck many people's lives. Although we cannot prevent most of these natural disasters, the more we know about them the better we can predict-and perhaps control the severity of their impact.

Equally important, but not always as well understood or appreciated, is the connection between geology and economic and political power. The distribution of mineral and energy resources is unequal, and no country is self-sufficient for all its mineral and energy needs. Throughout history, people have fought wars to secure needed mineral and energy resources. We need look no further than 1990-1991 to see that the United States became involved in the Gulf War largely because of the need to protect U.S. oil interest in that region. Mineral and energy availability and needs often shape foreign policy. The sanctions that the United States imposed on South Africa in 1986, for example, did not include most of the important minerals we had been importing and needed for our industrialized society, such as platinum-group minerals. Many foreign policies and treaties develop from the need to acquire and maintain adequate mineral and energy resources.

Most people are unaware of the extent to which geology affects their lives. For many people, the connection between geology and such well-publicized problems as nonrenewable energy and mineral resources, let alone waste disposal and pollution, is simply too far removed or too complex to fully appreciate. But consider for a moment just how dependent we are on geology in our daily routines.

Much electricity for appliances comes from burning coal, oil, or natural gas, or from uranium consumed in nuclear-generating plants. Geologists locate the coal, petroleum, and uranium. The copper or other metal wires through which electricity travels are manufactured from materials found as a result of mineral exploration. The buildings we live and work in owe their very existence to geologic resources. A few examples are the concrete foundation (concrete is a mixture of clay, sand, or gravel, and limestone), the drywall (made largely from the mineral gypsum), the windows (the mineral quartz is the principal ingredient in the manufacture of glass), and the metal or plastic plumbing fixtures inside the building (the metals are from ore deposits, and the plastics are most likely manufactured from petroleum distillates of crude oil).

Furthermore, when we go to work, our cars and public transport are powered and lubricated by some type of petroleum by-product and are constructed of metal alloys and plastics. And the roads or rails we ride over are made of geologic materials, such as gravel, asphalt, concrete, or steel. All these items are the result of processing geologic resources.

As individuals and societies, the standard of living we enjoy directly depends on the consumption of geologic materials. Therefore, we need to be aware of geology and of how our use and misuse of geologic resources may affect the delicate balance of nature and irrevocably alter our culture as well as our environment.

If we are to have a world in which poverty is not widespread, then we must develop policies that encourage management of our natural resources along with continuing economic development. A growing, global population will mean increased demand for food, water, and natural resources, particularly nonrenewable mineral and energy resources. Geologists will play an important role in locating the needed resources, as well as in protecting the environment for future generations.

Part 2: From "Basin and Range" by John McPhee

I used to sit in class and listen to the terms come floating down the room like paper airplanes. Geology was called a descriptive science, and with its pitted, outwash plains and drowned rivers, its hanging tributaries and starved coastlines, it was nothing if not descriptive. It was a fountain of metaphor - of isostatic adjustments and degraded channels, of angular unconformities and shifting divides, of rootless mountains and bitter lakes. Streams eroded headward, digging from two sides into mountain or hill, avidly struggling toward each other until the divide between them broke down, and the two rivers that did the breaking now became confluent (one yielding to the other, giving up its direction of flow and going the opposite way) to become a single stream. Stream capture. In the Sierra Nevada, the Yuba had captured the Bear. The Macho member of a formation in New Mexico was derived in large part from the solution and collapse of another formation. There was fatigued rock and incompetent rock and inequigranular fabric in rock. If you bent or folded rock, the inside of the curve was under great tension, and somewhere in the middle was the surface of no strain. Thrust fault, reverse fault, normal fault - the two sides were active in every fault. The inclination of a slope on which boulders would stay put was the angel of repose. There seemed, indeed, to be more than a little of the humanities in this subject. Geologists communicated in English; and they could name things in a manner that sent shivers through the bones. They had roof pendants in their discordant batholiths, mosaic conglomerates in desert pavement. There was ultrabasic, deep-ocean, mottled green-and-black - or serpentine. There was the slip face of the barchan dune.

In 1841, a paleontologist had decided that the big creatures of the Mesozoic were "fearfully great lizards," and had therefore named them dinosaurs. There were festooned crossbeds and limestone sinks, pillow lavas and petrified trees, incised meanders and defeated streams. There were dike swarms and slickensides, explosion pits, volcanic bombs. Pulsating glaciers. Hogbacks. Radiolarian ooze. There was almost enough resonance in some terms to stir the adolescent groin. The swelling up of mountains was described as an orogeny. Ontogeny, phylogeny, orogeny - accent syllable two. The Antler Orogeny, the Avalonian Orogeny, the Taconic, Acadian, Alleghenian Orogenies. The Laramide Orogeny. The center of the United States had had a dull geologic history - nothing much being accumulated, nothing much being eroded away. It was just sitting there conservatively. The East had once been radical - had been unstable, reformist, revolutionary, in the Paleozoic pulses of three or four orogenies. Now, for the last hundred and fifty million years, the East had been stable and conservative. The far-out stuff was in the Far West of the country - wild, weirdsma, a leather-jacket geology in mirrored shades, with its welded tuffs and Franciscan melange (internally deformed, complex beyond analysis), its strike-slip faults and falling buildings, its boiling springs and fresh volcanics, its extensional disassembling of the earth.

There was, to be sure, another side of the page -full of geological language of the sort that would have attracted Gilbert and Sullivan. Rock that stayed put was called autochthonous, and if it had moved it was allochthonous. "Normal meant "at right angles." "Normal" also meant a fault with a depressed hanging wall. There was a Green River Basin in Wyoming that was not to be confused with the Green River Basin in Wyoming. One was topographical and was on Wyoming. The other was structural and was under Wyoming. The Great Basin, which is centered in Utah and Nevada, was not to be confused with the Basin and Range, which is centered in Utah and Nevada. The Great Basin was topographical, and extraordinary in the world as a vastness of land that had no drainage to the sea. The Basin and Range was a realm of related mountains that coincided with the Great Basin, spilling over slightly to the north and considerably to the south. To anyone with a smoothly functioning bifocal mind, there was no lack of clarity about Iowa in the Pennsylvanian, Missouri in the Mississippian, Nevada in Nebraskan, Indiana in Illinoian, Vermont in Kansan, Texas in Wisconsinan time. Meteoric water, with study, turned out to be rain. It ran downhill in consequent, subsequent, obsequent, resequent, and not a few insequent streams.

As years went by, such verbal deposits would thicken. Someone developed enough effrontery to call a piece of our earth an epieugeosyncline. There were those who said interfluve when they meant between two streams, and a perfectly good word like mesopotamian would do. A cactolith, according to the American Geological Institute Glossary of Geology and Related Sciences, was "quasi-horizontal chonolith composed of anastomosing ductoliths, whose distal ends curl like a harpolith, thin like a sphenolith, or bulge dscordantly like an akmolityh or ethmolith." The same class of people who called on rock serpentine called another jacupirangite. Clinoptilolite, eclogite, migmatite, tincalconite, szaibleyite, pumpellyite. meyerhofferite. The same class of people who called one rock paracelisian called another despujolsite. Metakirchheimerite, phlogopite, katzenbuckelite, mboziite, noselite, neighborite, samsonite, pigeonite, muskoxite, pabstite, aenigmatite. Joesmithite.

With the X-ray diffractometer and the X-ray fluorescence spectrometer, which came into general use in geology laboratories in the late ninteen-fifties, and then with the electron probe (around 1970), geologists obtained ever closer examinations of the components of rock. What they had long seen through magnifying lenses as specimens held in the hand -or in thin slices under microscopes - did not always register identically in the eyes of these machines. Andesite, for example, had been given its name for being the predominant rock of the high mountains of South America. According to the machines, there is surprisingly little andesite in the Andes. The Sierra Nevada is renowned throughout the world for its relatively young and absolutely beautiful granite. There is precious little granite in the Sierra. Yosemite Falls, Half Dome, El Capitan - for the most part the "granite" of the Sierra is granodiorite.

It has always been difficult enough to hold in the mind that a magma which hardens in the earth as granite will - if it should flow out upon the earth - harden as rhyolite, that what hardens within the earth as diorite will harden upon the earth as andesite, that what hardens within the earth as gabbro will harden upon the earth as basalt, the difference from pair to pair being a matter of chemical composition and the differences within each pair being a matter of texture and of crystalline form, with the darker rock at the gabbro end and the lighter rock the granite. All of that - not to mention such wee appendixes as the fact that diabase is a special texture of gabbro - was difficult enough for the layman to remember before the diffractometers and the spectrometers and the electron probes came along to present their multiplex cavils. What had previously been described as the granite of the world turned out to be a large family of rock that included granodiorite, monzonite, syenite, adamellite, trondhjemite, alaskite, and a modest amount of true granite. A great deal of rhyolite, under scrutiny, became dacite, rhyodacite, quartz latite. Andesite was found to contain enough silica, potassium, sodium, and aluminum to be the fraternal twin of granodiorite. These points are pretty fine. The home terms still apply. The enthusiasm geologists show for adding new words to their conversation is, if anything, exceeded by their affection for the old. They are not about to drop granite. They say granodiorite when they are in church and granite the rest of the week.

Picture credits: "Research" pictures are from us. Mineral pictures are from "Simon and Schuster's Guide To Rocks & Minerals," edited by Prinz et al., 1978. Astronomical pictures are from NASA (http://antwrp.gsfc.nasa.gov/apod/). Other pictures are from the USGS (http://www.usgs.gov/).