Notes: Radiometric Dating

What is an atom? The smallest unit of matter All atoms with the same characteristics = an element

The Structure of Atoms Atoms have neutrons, protons, and electrons.

What is decay? Not all elements are stable. Unstable elements break down or decay over time. When atoms decay they release particles and energy. In radioactive decay, atoms break down to form stable elements (parent material >> daughter material)

Radioactive Decay

What is an atom’s half-life? The half-life is the time it takes for half of the radioactive element to decay. After each half-life there is half of the material we started with.

Iodine 131: half-life= 8days # of Half-lives # of Days Passed Amount Remaining 10 grams 1 8 5 grams 2 16 2.5 grams

How can we use it? Since the rate of decay is constant, we can use it like we use a clock! By measuring the amount of parent material and comparing it to the daughter material in the rock, the number of half-lives can be counted Geologists use radiometric dating to determine the absolute ages of rocks!

What rocks can we date with this method? Sed. and Met. rocks? No… they are both made of other rocks Ign. rocks? Yes! Scientists date extrusions and intrusions when possible.

The Age of the Earth The oldest rocks indicate that the earth is 4.6 billion years old!