# Radiometric dating and half life

Knowing about half-lives is important because it enables you to determine when a sample of radioactive material is safe to handle. Remember, the half-life is the time it takes for half of your sample, no matter how much you have, to remain. Of course, the mathematics are completely wrong. Strontium is a stable element that does not undergo radioactive change.

This date agrees with the age of the pyramid as estimated from historical records. Charcoal Sample, recovered from bed of ash near Crater Lake, Oregon, is from a tree burned in the violent eruption of Mount Mazama which created Crater Lake. This eruption blanketed several States with ash, providing geologists with an excellent time zone. Charcoal Sample collected from the "Marmes Man" site in southeastern Washington.

This rock shelter is believed to be among the oldest known inhabited sites in North America.

SQUISHY FACE FLIRT POLESpruce wood Sample from the Two Creeks forest bed near Milwaukee, Wisconsin, dates one of the last advances of the continental ice sheet into the United States. If the amount of carbon 14 is halved every 5, years, it will not take very long to reach an amount that is too small to analyze.

When finding the age of an organic organism we need to consider the half-life of carbon 14 as well as the rate of decay, which is —0. How old is the fossil? We can use a formula for carbon 14 dating to find the radiometric dating and half life. So, the fossil is 8, years old, meaning the living organism died 8, years ago.

WOMEN SEEKING MEN ELMIRA NYMath Central - mathcentral. In old rocks, there will be less potassium present than was required to form the mineral, because some of it has been transmuted to argon. The decrease in the amount of potassium required to form the original radiometric dating and half life has consistently confirmed the age as determined by the amount of argon formed.

Carbon dating: See Carbon 14 Dating in this web site. Rubidium-Strontium dating: The nuclide rubidium decays, with a half life of Strontium is a stable element; it does not undergo further radioactive decay.

Do not confuse with the highly radioactive isotope, strontium Strontium occurs naturally as a mixture of several nuclides, including the stable isotope strontium If three different strontium-containing minerals form at the same time in the same magma, each strontium containing mineral will have the same ratios of the different strontium nuclides, since all strontium nuclides behave the same chemically.

## RADIOMETRIC TIME SCALE

Note that this does not mean that the ratios are the same everywhere on earth. It merely means that the ratios are the same in the particular magma from which the test sample was later taken.

## 5.7: Calculating Half-Life

As strontium forms, its ratio to strontium will increase. Strontium is a stable element that does not undergo radioactive change. In addition, it is not formed as the result of a radioactive decay process.

Radiometric or Absolute Rock DatingThe amount of strontium in a given mineral sample will not change. It turns out to be a straight line with a slope of The corresponding half lives for each plotted point are marked on the line and identified.

MAN FINDS WOMAN LIVING IN HIS ATTICIt can be readily seen from the plots that when this procedure is followed with different amounts of Rb87 in different mineralsif the plotted half life points are connected, a straight line going through the origin is produced. These lines are called "isochrons". The steeper the slope of the isochron, the more half lives it represents. When the fraction radiometric dating and half life rubidium is plotted against the fraction of strontium for a number of different minerals from the same magma an isochron is obtained.

If the points lie on a straight line, this indicates that the data is consistent and probably accurate. An example of this can be found in Strahler, Fig However, if strontium 87 was present in the mineral when it was first formed from molten magma, that amount will be shown by an intercept of the isochron lines on the y-axis, as shown in Fig Thus it is possible to correct for strontium initially present.

Comparing figures The age of the sample can be obtained by choosing the origin at the y intercept.

## Nuclear Chemistry: Half-Lives and Radioactive Dating

In Fig Note that the amounts of rubidium 87 and strontium 87 are given as ratios to an inert isotope, strontium However, in calculating the ratio of Rb87 to Sr87, we can use a simple analytical geometry solution to the plotted data. Again referring to Fig. Since the half-life of Rb87 is