Absolute DatingEstablishing the Age of

Objects

1. Which best explains how geologic time scales can help scientists study the evolution of life on Earth?

A They describe the existence of rocks before there was life on Earth.B They show that geological features have evolved at the same rate as

organisms.C They compare the life histories of species that have used rocks as

habitats.D They correlate the existence of life on Earth with geological events.

2. Which source of water pollution includes oil and gasoline discharge from automobiles and storm sewer drainage?

A agricultureB bacteriaC sedimentationD urban runoff

What is it?• Establishing the age of an object by the

number of years it has existed• Remember what an isotope is?

– Unstable isotopes are radioactive

• Radioactive decay-isotopes breaking down from unstable to stable isotopes

• See Figure 1 on page 442

Parent Isotope

Radioactive Isotope of one Element

Daughter Isotope

Stable Isotope of one or more Elements

Constant Rate of Change

The More Daughter Material, the Older the Rock is.

http://www.inspiration.com/diagrams/up_images/radioactive_big.gif

Radiometric Dating

• Half-life-the time it takes one-half of a radioactive sample to decay

• Types of Radiometric dating– Potassium-Argon Method

– Uranium-Lead Method

– Rubidium-Strontium Method

– Carbon-14 Method

•How long would it take to spend one million dollars?On each day you can only spend half of what you start the day with.•If on January 1 you start with 1 million dollars, on what day will you end up with only one dollar or less?•Using the same rule, how long will it take to spend one hundred dollars?

•How old would an object be if the following fractions of carbon-14 remained;

•1/4, 1/8, 1/32, 1/64

•The half-life of carbon-14 is 5,730 years

Half-life Lab• What does your graph

look like?• Compare your results

with some one sitting next to you.

• What can you explain about half-life?

http://www.uwgb.edu/dutchs/GRAPHIC0/GenGeology/Halflife.gif