Physical Geology: Geologic Time Review Questions

Radiometric Dating Radiometric Dating – A Brief Explanation Radiometric dating is the primary dating scheme employed by scientists to determine the age of the earth. Radiometric dating techniques take advantage of the natural decay of radioisotopes. An isotope is one of two or more atoms which have the same number of protons in their nuclei, but a different number of neutrons. Radioisotopes are unstable isotopes: They continue to decay going through various transitional states until they finally reach stability. For example, Uranium U is a radioisotope. It will spontaneously decay until it transitions into Lead Pb The numbers and represent these isotopes’ atomic mass. In this instance, Uranium is called the “parent” and Lead is called the “daughter”. By measuring how long it takes for an unstable element to decay into a stable element and by measuring how much daughter element has been produced by the parent element within a specimen of rock, scientists believe they are able to determine the age of the rock.

Relative Vs. Absolute Dating: The Ultimate Face

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Radiohalos in the Shap Granite, Lake District, England huge thickness of sediments would have been the sediments on the pre-Flood ocean floor The conventional Ordovician age assigned to these Skiddaw Group between these ages for the Shap Granite obtained by three radioisotope dating methods (K-Ar, Rb-Sr, and U-Pb), it has been.

This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. July The Cheesewring , a granite tor A granite peak at Huangshan , China Granite containing rock is widely distributed throughout the continental crust. Outcrops of granite tend to form tors and rounded massifs.

Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels. Small dikes of granitic composition called aplites are often associated with the margins of granitic intrusions. In some locations, very coarse-grained pegmatite masses occur with granite. Origin[ edit ] Granite has a felsic composition and is more common in recent geologic time in contrast to Earth’s ultramafic ancient igneous history.

Felsic rocks are less dense than mafic and ultramafic rocks, and thus they tend to escape subduction , whereas basaltic or gabbroic rocks tend to sink into the mantle beneath the granitic rocks of the continental cratons. Therefore, granitic rocks form the basement of all land continents. Geochemical origins[ edit ] Granitoids have crystallized from magmas that have compositions at or near a eutectic point or a temperature minimum on a cotectic curve.

Magmas will evolve to the eutectic because of igneous differentiation , or because they represent low degrees of partial melting.

Radiometric Dating Methods

These are K-Ar data obtained on glauconite, a potassium-bearing clay mineral that forms in some marine sediment. Woodmorappe fails to mention, however, that these data were obtained as part of a controlled experiment to test, on samples of known age, the applicability of the K-Ar method to glauconite and to illite, another clay mineral. He also neglects to mention that most of the 89 K-Ar ages reported in their study agree very well with the expected ages.

Evernden and others 43 found that these clay minerals are extremely susceptible to argon loss when heated even slightly, such as occurs when sedimentary rocks are deeply buried. As a result, glauconite is used for dating only with extreme caution.

RADIOMETRIC TIME SCALE research has been the development and continuing refinement of the various methods and techniques used to measure the age of Earth materials. Precise dating has been accomplished since Conway Granite Samples collected from Redstone Quarry in the White Mountains of New Hampshire.

Equal Time for the Origin of Granite Introduction Creationists continue to push for equal time in science classrooms to teach that the Genesis stories in the Bible are valid scientific interpretations of earth history. Equal time for creationists’ interpretations is not likely to occur in secular universities and schools, but if the creationists are serious about equal time, then they should be open to granting equal time in their private Christian schools for presentations of both sides of a scientific issue — a literalist biblical view and the modern science view.

The origin, age, and other characteristic features of granite are such issues deserving equal time. However, Gentry , p , says that granite was formed both on Day 1 and Day 3 and that granite from both days can be mixed. He also claims that after Day 3, granite magmas must crystallize as rhyolite the fine-grained volcanic equivalent of granite , rather than coarse-grained granite, and that granites penetrating the Flood deposits result from upheavals of solids but not magma.

Austin states that the majority of conservative Christian scholars, including Henry Morris, believe that the earliest rocks formed on Day 1. He interprets these to include the Vishnu schists of the Grand Canyon into which the Proterozoic Zoroaster granites were intruded on Day 3, when land and sea were separated. If I were given equal time in a science classroom at a private, fundamentalist, Christian college or secondary school which advocated young-earth creationist views, I would provide the following material and information regarding the formation of granite.

This would allow students to compare a modern scientific interpretation of granite with the corresponding creationist biblical interpretation of granite being formed primarily in the Genesis Week.


Carbon , Radiometric Dating and Index Fossils Carbon dating is used to determine the age of biological artifacts up to 50, years old. This technique is widely used on recent artifacts, but educators and students alike should note that this technique will not work on older fossils like those of the dinosaurs alleged to be millions of years old. This technique is not restricted to bones; it can also be used on cloth, wood and plant fibers.

Carbon dating has been used successfully on the Dead Sea Scrolls, Minoan ruins and tombs of the pharaohs among other things.

absolute age dating exercise 1 2) If one metamorphic rock (that was a granite before metamorphism) gives a K/Ar date of million years and a U/Pb date of 1 billion years, what is each date telling us?

Unlike the radioactive isotopes discussed above, these isotopes are constantly being replenished in small amounts in one of two ways. The bottom two entries, uranium and thorium , are replenished as the long-lived uranium atoms decay. These will be discussed in the next section. The other three, Carbon , beryllium , and chlorine are produced by cosmic rays–high energy particles and photons in space–as they hit the Earth’s upper atmosphere.

Very small amounts of each of these isotopes are present in the air we breathe and the water we drink. As a result, living things, both plants and animals, ingest very small amounts of carbon , and lake and sea sediments take up small amounts of beryllium and chlorine

Multiple choice

Glossary Terms Introduction Stratigraphy is the study of rock layers and reconstruction of the original sequence in which they were deposited. The stratigraphy of an area provides the basis for putting together the geologic history of an area. The details of a region’s stratigraphic story are revealed by:

The rubidium-strontium dating method is a radiometric dating technique used by scientists to determine the age of rocks and minerals from the quantities they contain of specific isotopes of rubidium (87 Rb) and strontium (87 Sr, 86 Sr).

The principle states that in a sequence of undeformed sedimentary rocks the oldest beds are at the bottom and the youngest ones are at the top. Underlying assumptions are 1 that layers were originally deposited horizontally, 2 and that beds are not overturned sedimentary structures can be used to dermine whether a sedimentary succession is overturned or not. More on index fossils here. Faunal Succession is based on the observation that animals and animal communities that are preserved in sedimentary rocks change noticeably as geologic time passes evolution.

It was first recognized by William Smith, a British Surveyor, who while working on open cuts of canals, railroads, and roads, noticed that the fossils change systematically from the older towards the younger rocks. This principle has in the meanwhile been established to be true for all sediments worldwide, and is the basis of worldwide correlation of sedimentary rock units and one of the underpinnings of the theory of evolution. The image at left illustrates faunal succession.

In location A we have rock layers that successively have different types and combinations assemblages of fossils. If in location B we find the same fossil assemblage Assemblage 2 in a rock unit, we may assume that they are of essentially the same age as in location A. Obviously, the sedimentary rocks had to be there prior to emplacement of the igneous rocks, and thus they are older than the igneous rocks.

Conversely, the igneous rocks are younger than the sedimentary rocks. Other examples of cross crutting relationships can be related to faults fault has to be younger than the rock it is found in and unconformities see below.

Radiometric Dating Methods

His calculations did not account for heat produced via radioactive decay a process then unknown to science or, more significantly, convection inside the Earth, which allows more heat to escape from the interior to warm rocks near the surface. For biologists, even million years seemed much too short to be plausible. In Darwin’s theory of evolution , the process of random heritable variation with cumulative selection requires great durations of time. According to modern biology, the total evolutionary history from the beginning of life to today has taken place since 3.

Huxley , attacked Thomson’s calculations, suggesting they appeared precise in themselves but were based on faulty assumptions.

The nitty gritty on radioisotopic dating. Radioisotopic dating is a key tool for studying the timing of both Earth’s and life’s history. This suite of techniques allows scientists to figure out the dates that ancient rock strata were laid down — and hence, provides information about geologic processes, as well as evolutionary processes that acted upon the organisms preserved as fossils in.

Therefore RATE must propose that almost all of this decay occurred during the one-year flood, because for some unknown reason the decay rate for some atoms but not others was extremely high but only for a year, not before or after. This amount of decay would produce an immense amount of heat quickly, in less than a year. This would be a “super-catastrophic flood” producing results far beyond anything we actually observe in the geological record of the earth.

In addition to this heat-producing radioactive decay, young-earth explanations for flood geology require other heat-producing processes — volcanic magma, limestone formation, meteor impacts, biological decay, plus more heat with any of the models Vapor Canopy, Hydroplate, Comet, Runaway Subduction proposed to answer the question, “Where did the Flood water come from, and where did it go? Is there a young-earth solution? No known thermodynamic process could account for the required rate of heat removal nor is there any known way to protect organisms from radiation damage.

Yet they are so confident that these problems will be resolved that they encourage a message that the reliability of [their young-earth interpretation of] the Bible has been confirmed.

Practice questions: Geologic Time

And a Parisian-inspired central courtyard with a three-story-high green wall, studded with orchids, bromeliads and other tropical plants. Overlooked by an infinity pool. And rimmed by a sequence of airy, open-plan spaces. After three years of work, involving the same techniques and materials used to erect skyscrapers, it is now an occupied house again — if you can call a sprawling 17, square-foot urban villa a house.

This data is reproduced from Dalrymple, The Age of the Earth * Note that 40 K also decays to 40 Ca with a decay constant of x yr-1, but that decay is not used for half-life is for the parent isotope and so includes both decays.

The event took place at Macalester College in St. Paul, and was led by Jeff Thole , laboratory supervisor and instructor in the college’s Geology Department. Jeff is extremely knowledgeable and enthusiastic about geology, and in the course of cramming a semester’s worth of geology into the two hour lab, he mentioned that he had in his office one of the oldest rocks in the world: After finishing his talk about the rock cycle, and as everyone began examining the variety of rock types spread out on lab tables in several rooms, Jeff brought out the chunk of ancient gneiss for everyone to see.

Found on an island in the extreme and very isolated northern regions of Canada’s Northwest Territories, the Acasta gneiss has been radiometrically dated to be upwards to 4. That’s a number that’s not very easy to comprehend. The Earth itself is estimated to be just a half-billion years older, so the Acasta gneiss pronounced nice is some of the very earliest crustal rock still existing on Earth’s ever-changing surface.

For a rock unit to withstand 4 billion years of the rock cycle – where the forces of erosion and plate tectonics are constantly at work wearing down, reworking and remelting rocks – that’s quite a feat if you think about it. To give you a better idea of the vast amount of time we’re talking about here, let’s first reduce it to a more comprehendible time-frame.

localhost:81 #18 – Absolute radiometric age dating of rocks and geologic materials