8.3 Radioactive Dating. Lesson Objective 4d Today, we will learn that evidence from geologic layers and radioactive dating indicates Earth is approximately.

8.3 Radioactive Dating

Lesson Objective

4d

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

Key Terms atomelementradioactive decayhalf-life

Radioactive Radioactive DecayDecay

AtomsAtoms = tiny particles that = tiny particles that make up all mattermake up all matter

ElementElement = matter that = matter that contains atoms of only one contains atoms of only one type; current elements type; current elements found in found in Periodic Table of Periodic Table of ElementsElements

Radioactive decay Radioactive decay = the = the process by which process by which unstable unstable atomsatoms break down break down releasing particles and releasing particles and energyenergy

Radioactive Radioactive DecayDecay

Atoms of one element Atoms of one element break downbreak down or or decaydecay to to form the atoms of another form the atoms of another element.element.

Radioactive elements Radioactive elements occur naturally in occur naturally in

igneous rock.igneous rock.Scientists use the Scientists use the rate of rate of decaydecay of elements within a of elements within a rock to determine the rock to determine the absolute age of a rockabsolute age of a rock

Rate of DecayRate of Decay• The composition of rock The composition of rock containing radioactive containing radioactive elements changes slowly elements changes slowly over time.over time.

• The amount of radioactive The amount of radioactive element goes down while the element goes down while the amount of new element goes amount of new element goes up.up.

• The rate of decay for a The rate of decay for a specific element is constant.specific element is constant.

The The hhalf-lifealf-life of an element is of an element is the time it takes for half of the time it takes for half of the radioactive atoms to the radioactive atoms to decay.decay.

Half-LifeHalf-LifeExample:Example: Potassium-40 Potassium-40 has a has a half-life of 1.3 billion half-life of 1.3 billion yearsyears

After 3 half-lives, how After 3 half-lives, how much of the radioactive much of the radioactive element remains?element remains?

Calculating the Calculating the Absolute Age of a Absolute Age of a

RockRock

1.1. Measure the amount of Measure the amount of radioactive element in a radioactive element in a rock.rock.

2.2. Measure the amount of Measure the amount of stable element in a rock.stable element in a rock.

3. Calculate ratio to 3. Calculate ratio to determine age.determine age.

Radioactive ElementsRadioactive Elementsuseful in dating rocksuseful in dating rocksand fossils:and fossils:Potassium-Argon:Potassium-Argon:

Potassium-40 useful in Potassium-40 useful in dating the most ancient dating the most ancient rocks because of its long rocks because of its long half-life.half-life.

Carbon-14:Carbon-14:

Carbon-14 decays to Carbon-14 decays to Nitrogen-14 with a half-life Nitrogen-14 with a half-life of 5,730 years. Useful in of 5,730 years. Useful in dating fossils that lived up dating fossils that lived up to about 50,000 years ago.to about 50,000 years ago.

The Age of EarthThe Age of EarthRadioactive dating of Radioactive dating of oldest rocks found indicate oldest rocks found indicate earth to be about 4.0 earth to be about 4.0 billion years old.billion years old.

Scientists determined the Scientists determined the age of rocks brought back age of rocks brought back from the moon to be about from the moon to be about 4.6 billion years old.4.6 billion years old.

Since Earth is slightly older Since Earth is slightly older than moon, Earth is than moon, Earth is considered to be slightly considered to be slightly more than 4.6 billion years more than 4.6 billion years old.old.

The EndThe End