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The radioactive decay of rubidium 87 Rb to strontium 87 Sr was the first widely used dating system that utilized the isochron method. Because rubidium is concentrated in crustal rocks, the continents have a much higher abundance of the daughter isotope strontium compared with the stable isotopes.

A ratio for average continental crust of about 0. This difference may appear small, but, considering that modern instruments can make the determination to a few parts in 70, it is quite significant. Dissolved strontium in the oceans today has a value of 0. Thus, if well-dated, unaltered fossil shells containing strontium from ancient seawater are analyzed, changes in this ratio with time can be observed and applied in reverse to estimate the time when fossils of unknown age cost of k ar dating deposited.

The rubidium—strontium pair is ideally suited for the isochron dating of igneous rocks. As a liquid rock cools, first one mineral and then another achieves saturation and precipitates, each extracting specific elements in the process. Strontium is extracted in many minerals that are formed early, whereas rubidium is gradually concentrated in the final liquid phase.

In practice, rock samples weighing several kilograms each are collected from a suite of rocks that are believed to have been part of a single homogeneous liquid prior to solidification. The samples are crushed and homogenized to produce a fine representative rock powder from which a fraction of a gram is withdrawn and dissolved in the presence of appropriate isotopic traces, or spikes.

Strontium and rubidium are extracted and loaded into the mass spectrometer, and the values appropriate to the x and y coordinates are calculated from the isotopic ratios measured. Once plotted as R1 p i. Using estimates of measurement precision, the crucial question of whether or not scatter outside of measurement error exists is addressed.

Such scatter would constitute a geologic component, indicating that one or more of the underlying assumptions has been violated and that the age indicated is probably not valid. For an isochron to be valid, each sample tested must 1 have had the same initial ratio, 2 have been a closed system over geologic time, and 3 have the same age. Well-preserved, unweathered rocks that crystallized rapidly and have not been subjected to major reheating events are most likely to give valid isochrons.

Weathering is a disturbing influence, as is leaching or exchange by hot crustal fluids, since many secondary minerals contain rubidium. Volcanic rocks are most susceptible to such changes because their minerals are fine-grained and unstable glass may be present. Cost of k ar dating the other hand, meteorites that have spent most of their time in the deep freeze of outer space can provide ideal samples. Potassium -bearing minerals including cost of k ar dating varieties of mica, are ideal for rubidium—strontium dating as they have abundant parent rubidium and a low abundance cost of k ar dating initial strontium.

When minerals cost of k ar dating a low-rubidium or a high-strontium content are analyzed, the isochron-diagram approach can be used cost of k ar dating provide an evaluation of the data.

As discussed above, rubidium—strontium mineral ages need not be identical in a rock with a complex thermal historyso that results may junge sexy asian models sex meaningful in terms of dating the last heating event but not cost of k ar dating terms of the actual age of a rock.

Article Media. Info Print Print. Table Of Contents. Submit Feedback. Thank you for your cost of k ar dating. Load Previous Page. Rubidium—strontium method The radioactive decay of rubidium 87 Rb to strontium 87 Sr was the first widely used dating system that utilized the isochron method. Dating simple igneous rocks The rubidium—strontium pair is ideally suited for the isochron dating of igneous rocks.

Dating minerals Potassium -bearing minerals including several varieties of mica, are ideal for rubidium—strontium dating as they have abundant parent rubidium and a low abundance of initial strontium.

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