A Fossil. Any method of measuring the age of an event or object in years.

A Fossil

Any method of measuring the age of an event or object in years.

Radioactive decay Radiometric dating

Radioactive – unstable isotope

Atoms of the same element have the same # of protons but different # of neutrons.

Not having the same number of protons and neutrons in an element.

Stable- same number of protons and neutrons in an element.

Tend to break down into stable isotopes of the same or other elements in a process.

Proton (p+)

Neutron (n◦)

Electron cloud – holds the electrons

Nucleus – center of an atom.

Radioactive decay – when some unstable isotopes decay, a neutron is converted into a proton. In the process, an e- (electron) is released.

Parent Daughter

(6 protons and 8 neutrons) (7 protons and 7 neutrons)Unstable isotope Stable Isotope

Scientist compare the amount of parent material (p & n) with the amount of daughter material (p & n). The more daughter material there is, the older the rock.

Based on the ratio of parent material to daughter material.

The ratio is determined by the number (#) of half-life.

(Half – life - the time it takes 1 half-life of radioactive sample to decay).

Unstable isotope to stable isotope

Potassium-Argon Method Potassium 40 has a half-life of 1.3 billion years. Decays to Argon and calcium. Argon is measured as the daughter isotope. Used to date rocks older than 100,000 years.

Uranium-Lead Method Uranium 238 decays to Lead 206. Half-life of Uranium 238 is 4.5 billion years. The older the rock, the more daughter material (lead 206)

there will be. Younger rock does not have enough daughter material to be measured using this method.

Uranium –Lead can be used to date rocks more than 10 million years old.

Rubidium-strontium Method – The unstable parent isotope Rubidium 87 forms the stable

daughter Strontium 87. Half-life of Rubidium 87 is 49 billion years. Used to date rocks older than 10 million years.

Carbon 14 method – Half-life of Carbon 14 is only 5,730 years. Used mainly for dating things that lived within the last

50,000 years.

During radioactive decay, an unstable isotope decays at a constant rate and becomes a stable isotope of the same or a different element.

Radiometric dating, based on the ratio of parent to daughter material, is used to determine the absolute age of a sample.

Methods of radiometric dating include potassium-argon, uranium-lead, rubidium-strontium, and carbon-14 dating.