# Radioactive Dating

Dating techniques are procedures used by scientists to determine the age of a specimen. 2 types of Dating:

*Relative Dating

*Absolute Dating

Relative Dating

-methods tell only if one sample is older or younger than another sample. -They do not provide an age in years.

Stratigraphy

-Main Relative Dating Method

-is the study of layers of rocks or the objects embedded within those layers. -based on the assumption that deeper layers were deposited earlier, and thus are older than more shallow layers. Seriation

is the ordering of objects according to their age.

James Ford - used seriation to determine the chronological order of American Indian pottery styles in the Mississippi Valley. Absolute dating

* any method of measuring the age of an event or object in years. * To determine the absolute ages of fossils and rocks,

* scientists analyze isotopes of radioactive elements. Isotopes

* atoms of the same element that have the same number of protons but different numbers of neutrons. * Most isotopes are stable, meaning that they stay in their original form. * Other isotopes are unstable.

* Scientists call unstable isotopes radioactive.

Radioactive decay

* Radioactive isotopes tend to break down into stable isotopes of the same or other elements. * Refers to the process in which a radioactive form of an element is converted into a decay product at a regular rate. - This dating is not a single method of absolute dating but instead a group of related methods for absolute dating of samples. * Because radioactive decay occurs at a steady rate,

* Scientists can use the relative amounts of stable and unstable isotopes present in an object to determine the object’s age. Dating Rocks — How Does It Work?

* In radioactive decay, an unstable radioactive isotope of one element breaks down into a stable isotope. * The stable isotope may be of the same element or of a different element. Parent isotope

* The unstable radioactive isotope.

Daughter isotope

* The stable isotope produced by the radioactive decay of the parent isotope. * The rate of radioactive decay is constant so scientists can compare the amount of parent material with the amount of daughter material to date rock. The more daughter material there is the older the rock is.

Absolute Dating Methods

* Cation-Ratio Dating – used to date rock surfaces such as stone artifacts and cliff and ground drawings. -this technique can only be applied to rocks from desert areas, where the varnish is most stable. *Thermoluminescence Dating – very useful for determining the age of pottery. Has the advantage of covering the time interval between radiocarbon and pottasium-argon dating or 40,000,000 years. *Optically Stimulated Luminescence (OSL) - very similar to thermoluminescence dating, both of which are considered “clock setting”. * This technique can be used to determine the age of unheated sediments les than 500,000 years old. * a disadvantage to this technique is that in order to get accurate results, the sediment to be tested cannot be exposed to light, making sampling difficult. Radiometric Dating

Determining the absolute age of a sample, based on the ratio of parent material to daughter material. If you know the rate of decay for a radioactive element in a rock you can figure out the absolute age of the rock.

Half-life

* the time needed for half of a sample of a radioactive substance to undergo radioactive decay. After every half-life, the amount of parent material decrease by one-half. Types of Radiometric Dating

* Scientists use different radiometric-dating methods based on the estimated age of an object. * There are four radiometric-dating techniques.

1. Potassium-Argon Method

* Potassium-40 has a half-life of 1.3 billion years, and it decays leaving a daughter material of argon. * This method is used mainly to date...

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