Radioactive Dating Worksheet Answers | ВКонтакте
Radon fraction (eeA') remaining after radioactive decay for specified times -. 2. Recommended 2. TECHNIQUES. OF WATER-RESOURCES. INVESTIGATIONS when possible. proximately 30 d starting as close to zero time as possible. A secondary school revision resource for OCR Gateway GCSE Additional Science about radiation and uses of radioisotopes. 2. 2 All the C will be gone after. Class. Radioactive Dating. Study the diagram below. obtained from the potassium/argon dating method (the most cited method)?. Some examples use negative values of ctive dating - worksheet pd.
This temperature is what is known as closure temperature and represents the temperature below which the mineral is a closed system to isotopes. Thus an igneous or metamorphic rock or melt, which is slowly cooling, does not begin to exhibit measurable radioactive decay until it cools below the closure temperature. The age that can be calculated by radiometric dating is thus the time at which the rock or mineral cooled to closure temperature.
This field is known as thermochronology or thermochronometry. The age is calculated from the slope of the isochron line and the original composition from the intercept of the isochron with the y-axis.
Radiometric dating - Wikipedia
The equation is most conveniently expressed in terms of the measured quantity N t rather than the constant initial value No. The above equation makes use of information on the composition of parent and daughter isotopes at the time the material being tested cooled below its closure temperature. This is well-established for most isotopic systems. Plotting an isochron is used to solve the age equation graphically and calculate the age of the sample and the original composition.
Modern dating methods[ edit ] Radiometric dating has been carried out since when it was invented by Ernest Rutherford as a method by which one might determine the age of the Earth.
In the century since then the techniques have been greatly improved and expanded. The mass spectrometer was invented in the s and began to be used in radiometric dating in the s.
It operates by generating a beam of ionized atoms from the sample under test. The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as " Faraday cups ", depending on their mass and level of ionization. On impact in the cups, the ions set up a very weak current that can be measured to determine the rate of impacts and the relative concentrations of different atoms in the beams.
Uranium—lead dating method[ edit ] Main article: Uranium—lead dating A concordia diagram as used in uranium—lead datingwith data from the Pfunze BeltZimbabwe. This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years. Zircon has a very high closure temperature, is resistant to mechanical weathering and is very chemically inert. Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of the event.How Carbon Dating Works
This can be seen in the concordia diagram, where the samples plot along an errorchron straight line which intersects the concordia curve at the age of the sample. Samarium—neodymium dating method[ edit ] Main article: Samarium—neodymium dating This involves the alpha decay of Sm to Nd with a half-life of 1. Accuracy levels of within twenty million years in ages of two-and-a-half billion years are achievable.
Potassium—argon dating This involves electron capture or positron decay of potassium to argon Potassium has a half-life of 1. Rubidium—strontium dating method[ edit ] Main article: Rubidium—strontium dating This is based on the beta decay of rubidium to strontiumwith a half-life of 50 billion years. This scheme is used to date old igneous and metamorphic rocksand has also been used to date lunar samples.
Closure temperatures are so high that they are not a concern. Rubidium-strontium dating is not as precise as the uranium-lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample. Uranium—thorium dating method[ edit ] Main article: Uranium—thorium dating A relatively short-range dating technique is based on the decay of uranium into thorium, a substance with a half-life of about 80, years.
It is accompanied by a sister process, in which uranium decays into protactinium, which has a half-life of 32, years. While uranium is water-soluble, thorium and protactinium are not, and so they are selectively precipitated into ocean-floor sedimentsfrom which their ratios are measured.
The scheme has a range of several hundred thousand years. The basic principle Carbon has three naturally occurring isotopeswith atoms of the same atomic number but different atomic weights. They are 12C, 13C and 14C. C being the symbol for carbon and the isotopes having atomic weights 12, 13 and The three isotopes don't occur equally either, The radiocarbon dating method is based on the rate of decay of the radioactive or unstable 14C which is formed in the upper atmosphere through the effect of cosmic ray neutrons upon nitrogen The reaction is as follows: The carbon dioxide mixes throughout the atmosphere, dissolves in the oceans, and via photosynthesis enters the food chain to become part of all plants and animals.
In principle the uptake rate of 14C by animals is in equilibrium with the atmosphere. As soon as a plant or animal dies, they stop the metabolic function of carbon uptake and with no replenishment of radioactive carbon, the amount of 14C in their tissues starts to reduce as the 14C atoms decay.
Like carbon, the shorter-lived uranium-series isotopes are constantly being replenished, in this case, by decaying uranium supplied to the Earth during its original creation. Following the example of carbon, you may guess that one way to use these isotopes for dating is to remove them from their source of replenishment. This starts the dating clock. In carbon this happens when a living thing like a tree dies and no longer takes in carbonladen CO2.
For the shorter-lived uranium-series radionuclides, there needs to be a physical removal from uranium. The chemistry of uranium and thorium are such that they are in fact easily removed from each other. Uranium tends to stay dissolved in water, but thorium is insoluble in water.
So a number of applications of the thorium method are based on this chemical partition between uranium and thorium. Sediments at the bottom of the ocean have very little uranium relative to the thorium. Because of this, the uranium, and its contribution to the thorium abundance, can in many cases be ignored in sediments. Thorium then behaves similarly to the long-lived parent isotopes we discussed earlier. It acts like a simple parent-daughter system, and it can be used to date sediments.
On the other hand, calcium carbonates produced biologically such as in corals, shells, teeth, and bones take in small amounts of uranium, but essentially no thorium because of its much lower concentrations in the water. This allows the dating of these materials by their lack of thorium. A brand-new coral reef will have essentially no thorium As it ages, some of its uranium decays to thorium While the thorium itself is radioactive, this can be corrected for.
Comparison of uranium ages with ages obtained by counting annual growth bands of corals proves that the technique is page. The method has also been used to date stalactites and stalagmites from caves, already mentioned in connection with long-term calibration of the radiocarbon method.
In fact, tens of thousands of uranium-series dates have been performed on cave formations around the world.
Previously, dating of anthropology sites had to rely on dating of geologic layers above and below the artifacts. But with improvements in this method, it is becoming possible to date the human and animal remains themselves. Work to date shows that dating of tooth enamel can be quite reliable. However, dating of bones can be more problematic, as bones are more susceptible to contamination by the surrounding soils. As with all dating, the agreement of two or more methods is highly recommended for confirmation of a measurement.
If the samples are beyond the range of radiocarbon e. Non-Radiometric Dating Methods for the PastYears We will digress briefly from radiometric dating to talk about other dating techniques. It is important to understand that a very large number of accurate dates covering the pastyears has been obtained from many other methods besides radiometric dating.
We have already mentioned dendrochronology tree ring dating above. Dendrochronology is only the tip of the iceberg in terms of non-radiometric dating methods. Here we will look briefly at some other non-radiometric dating techniques. One of the best ways to measure farther back in time than tree rings is by using the seasonal variations in polar ice from Greenland and Antarctica.
There are a number of differences between snow layers made in winter and those made in spring, summer, and fall. These seasonal layers can be counted just like tree rings.
The seasonal differences consist of a visual differences caused by increased bubbles and larger crystal size from summer ice compared to winter ice, b dust layers deposited each summer, c nitric acid concentrations, measured by electrical conductivity of the ice, d chemistry of contaminants in the ice, and e seasonal variations in the relative amounts of heavy hydrogen deuterium and heavy oxygen oxygen in the ice.
These isotope ratios are sensitive to the temperature at the time they fell as snow from the clouds. The heavy isotope is lower in abundance during the colder winter snows than it is in snow falling in spring and summer.
So the yearly layers of ice can be tracked by each of these five different indicators, similar to growth rings on trees. The different types of layers are summarized in Table III.
Page 17 Ice cores are obtained by drilling very deep holes in the ice caps on Greenland and Antarctica with specialized drilling rigs. As the rigs drill down, the drill bits cut around a portion of the ice, capturing a long undisturbed "core" in the process.
These cores are carefully brought back to the surface in sections, where they are catalogued, and taken to research laboratories under refrigeration. A very large amount of work has been done on several deep ice cores up to 9, feet in depth. Several hundred thousand measurements are sometimes made for a single technique on a single ice core.
A continuous count of layers exists back as far asyears. In addition to yearly layering, individual strong events such as large-scale volcanic eruptions can be observed and correlated between ice cores.
A number of historical eruptions as far back as Vesuvius nearly 2, years ago serve as benchmarks with which to determine the accuracy of the yearly layers as far down as around meters. As one goes further down in the ice core, the ice becomes more compacted than near the surface, and individual yearly layers are slightly more difficult to observe.
For this reason, there is some uncertainty as one goes back towardsyears. Recently, absolute ages have been determined to 75, years for at least one location using cosmogenic radionuclides chlorine and beryllium G. These agree with the ice flow models and the yearly layer counts.
Note that there is no indication anywhere that these ice caps were ever covered by a large body of water, as some people with young-Earth views would expect. Polar ice core layers, counting back yearly layers, consist of the following: Visual Layers Summer ice has more bubbles and larger crystal sizes Observed to 60, years ago Dust Layers Measured by laser light scattering; most dust is deposited during spring and summer Observed toyears ago Layering of Elec-trical Conductivity Nitric acid from the stratosphere is deposited in the springtime, and causes a yearly layer in electrical conductivity measurement Observed through 60, years ago Contaminant Chemistry Layers Soot from summer forest fires, chemistry of dust, occasional volcanic ash Observed through 2, years; some older eruptions noted Hydrogen and Oxygen Isotope Layering Indicates temperature of precipitation.
Heavy isotopes oxygen and deuterium are depleted more in winter. Yearly layers observed through 1, years; Trends observed much farther back in time Varves. Another layering technique uses seasonal variations in sedimentary layers deposited underwater.
The two requirements for varves to be useful in dating are 1 that sediments vary in character through the seasons to produce a visible yearly pattern, and 2 that the lake bottom not be disturbed after the layers are deposited.
These conditions are most often met in small, relatively deep lakes at mid to high latitudes. Shallower lakes typically experience an overturn in which the warmer water sinks to the bottom as winter approaches, but deeper lakes can have persistently thermally stratified temperature-layered water masses, leading to less turbulence, and better conditions for varve layers. Varves can be harvested by coring drills, somewhat similar to the harvesting of ice cores discussed above. Overall, many hundreds of lakes have been studied for their varve patterns.
Each yearly varve layer consists of a mineral matter brought in by swollen streams in the spring. Regular sequences of varves have been measured going back to about 35, years. The thicknesses of the layers and the types of material in them tells a lot about the climate of the time when the layers were deposited.
For example, pollens entrained in the layers can tell what types of plants were growing nearby at a particular time. Other annual layering methods. Besides tree rings, ice cores, and sediment varves, there are other processes that result in yearly layers that can be counted to determine an age.