1. ABSOLUTE-AGE DATING: A MEASURE OF GEOLOGIC TIME

2. THINK ABOUT IT… How old is the Earth? Can it be determined? What are some tools or methods that scientists could use to figure out the age of the Earth?

3. THE RELATIVE AGE DATING METHOD IS NOT AN EXACT SCIENCE Relative-Age Dating techniques use the layering of rocks (and fossils contained within them) to determine age. The older rocks are on bottom, the younger rocks are on top. This is an “estimate” of geologic age.

4. WHAT IF YOU WANT TO KNOW THE EXACT AGE OF ROCKS OR FOSSILS? Finding the exact age of an object is called absolute dating. Remember, absolute means “exact” or “definite”.

5. RADIOACTIVE DECAY Radioactive decay is an absolute-age dating technique. To determine the absolute ages of fossils and rocks, scientists analyze isotopes of radioactive elements. Unstable isotopes decay, or break down, over time. The original atom is called the parent isotope. The new form of the atom is called the daughter element.

6. RADIOACTIVE DECAY CONTINUED The parent is the unstable atom The daughter is the new atom

7. RADIOACTIVE DECAY CONTINUED This occurs at a constant rate and can be analyzed to determine exact age The more daughter element there is, the older a rock is.

8. HALF-LIFE The amount it takes for one half of the parent isotope to decay into the daughter element is called a half-life.

9. RADIOMETRIC DATING Radiometric dating determines the age of rocks and fossils that undergo radioactive decay. If you know the rate of decay for a radioactive isotope in a rock, you can figure out the absolute age of that rock or fossil. Common types of radiometric dating include: Uranium-Lead Method potassium-Argon Method Rubidium-Strontium Method Carbon-14 Method

10. URANIUM-LEAD METHOD POTASSIUM-ARGON METHOD RUBIDIUM-STRONTIUM METHOD These methods are used to determine the age of rocks from 100,000 years to 10 million years old.

11. CARBON-14 METHOD The carbon-14 method can be used to determine the age of anything that lived within the last 50,000 years.

12. ABSOLUTE AGE DATING AND EARTH By counting the number of parent isotopes and daughter elements in some very old rocks, scientists have determined the age of the Earth to be 4.6 billion years.