1. 8.3 Radioactive Dating

2. Lesson Objective 4d
Today, we will learn that evidence from geologic layers and radioactive dating indicates Earth is approximately 4.6 billion years old.

3. Key Terms
atom
element
radioactive decay
half-life

4. Radioactive Decay Atoms = tiny particles that make up all matter
Element = matter that contains atoms of only one type; current elements found in Periodic Table of Elements
Radioactive decay = the process by which unstable atoms break down releasing particles and energy

5. Radioactive elements occur naturally in igneous rock.
Radioactive Decay
Atoms of one element break down or decay to form the atoms of another element.
Radioactive elements occur naturally in igneous rock.
Scientists use the rate of decay of elements within a rock to determine the absolute age of a rock

6. Rate of Decay
The composition of rock containing radioactive elements changes slowly over time.
The amount of radioactive element goes down while the amount of new element goes up.
The rate of decay for a specific element is constant.
The half-life of an element is the time it takes for half of the radioactive atoms to decay.

7. Half-Life Example: Potassium-40 has a half-life of 1.3 billion years
After 3 half-lives, how much of the radioactive element remains?

8. Calculating the Absolute Age of a Rock
Measure the amount of radioactive element in a rock.
2. Measure the amount of stable element in a rock.
3. Calculate ratio to determine age.

9. Radioactive Elements useful in dating rocks and fossils:
Potassium-Argon:
Potassium-40 useful in dating the most ancient rocks because of its long half-life.
Carbon-14:
Carbon-14 decays to Nitrogen-14 with a half-life of 5,730 years. Useful in dating fossils that lived up to about 50,000 years ago.

10. The Age of Earth
Radioactive dating of oldest rocks found indicate earth to be about 4.0 billion years old.
Scientists determined the age of rocks brought back from the moon to be about 4.6 billion years old.
Since Earth is slightly older than moon, Earth is considered to be slightly more than 4.6 billion years old.

11. The End