Absolute Dating Radioactive Dating

Radioactivity Almost all of the elements contain radioactive isotopes Isotopes are atoms of the same element with different atomic weights This is due to different numbers of neutrons in the nucleus.

Radioactivity The rate at which radioactive elements break down is predictable and specific to different isotopes. The rate of decay is not affected by external factors such as temperature, heat or pressure

Radioactivity We measure time of decay in Half-Life A Half-Life is the time it takes for the mass of one half of the radioactive element to decay into its daughter product.

A graph of radioactive decay looks like this: How many half-lives have occurred when only 12.5% of the parent material is left? 3

B D 13 X 10^9 YEARS

Absolute Dating By comparing the ratio of Parent product to daughter product you can calculate the number of half-lives that have passed Materials with long half-lives are used to date old materials (Uranium, Thorium, Plutonium) Materials with short half-lives are used to date young materials (Carbon)

Absolute Dating The age of the Earth was determined by the breakdown of different isotopes of uranium.

Absolute Dating Carbon 14 (C14) is often used to date materials that were once alive. While the organism is living the amount of C14 remains constant because of the exchange of carbon

Absolute Dating When the organism dies the C14 breaks down into N 14 Due to the relatively short half-life of 5700 years C14 is not useful for dating very old objects

6 grams

Brain Dump: The following fossil starts with 24 grams of carbon. It loses ½ of that every 1000 years. How old is it when it has: 24 grams: 0 years old 12 grams: 1,oo0 years old 6 grams: 2,000 years old

Brain Dump: The following fossil starts with 48 grams of carbon. It loses ½ of that every 2 million years. How old is it when it has: 48 grams: 0 years old 24 grams: 2 million years old 12 grams: 4 million years old