• This principle states that sedimentary layers are originally laid down horizontally.

STARTER

Relative-Age Dating

• absolute age

• isotope

• radioactive decay

• half-life

Absolute-Age Dating

• Scientists use the term absolute age to mean the numerical age, in years, of a rock or object.

Absolute Ages of Rocks

• Scientists have been able to determine the absolute ages of rocks and other objects since the beginning of the twentieth century, when radioactivity was discovered.

• Radioactivity is the release of energy from unstable atoms.

Absolute Ages of Rocks (cont.)

How is absolute age different from relative age?

All atoms of a given element have the same number of protons.

• Isotopes are atoms of the same element that have different numbers of neutrons.

• Stable isotopes do not change under normal conditions.

Atoms

Radioactive decay is the process by which an unstable element naturally changes into another element that is stable.

• The rate of decay is constant for a given isotope and measured in time units called half-lives.

• An isotope’s half-life is the time required for half of the parent isotopes to decay into daughter isotopes.

• Half-lives of radioactive isotopes range from a few microseconds to billions of years.

Atoms (cont.)

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• Because radioactive isotopes decay at a constant rate, they can be used to measure the age of the material that contains them.

• Radiometric dating is the process in which scientists measure the ratio of the amount of parent isotope to daughter product in a sample of the material they want to date.

Radiometric Ages

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Homework:

Read pg. 344-350 and complete worksheet

Extra Credit:

Ancient Mysteries and Carbon-14 Dating

• Absolute age is the age in years of a rock or object.

• The radioactive decay of unstable isotopes occurs at a constant rate, measured as half-life.

• To date a rock or object, scientists measure the ratios of its parent and daughter isotopes.

Lesson 3: Absolute-Age Dating

A. an isotope

B. a neutron

C. a stable element

D. a proton

Radioactive decay is the process by which an unstable element naturally changes into which of these?

A. age

B. radiometric date

C. rate of decay

D. half-life

Which of these refers to the time required for half of the parent isotopes to decay into daughter isotopes?

A. neutrons

B. atoms

C. protons

D. parent isotopes

Isotopes are atoms of the same element that have different numbers of what?