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Table of Contents. Titles: Age and Time Page #: 13 Date: 9/12/12. Objective. Students will be able to describe the method that scientists use to date the age of the earth. Students will be able to define the half life of a molecule. Words of the Day.

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Presentation Transcript

• Titles: Age and Time

• Page #: 13

• Date: 9/12/12

• Students will be able to describe the method that scientists use to date the age of the earth.

• Students will be able to define the half life of a molecule.

• Isotope: Molecules with unstable nuclei that give off particles at a constant rate.

• Half Life: The time over which 1/2 of the atoms in a radioactive isotope decay.

### Age and TimeAge of Earth:

Earth is between 4.5 and 4.6 Billion years old.

Early scientists had dated Earth from being ~ 4000 years old to 1.64 Billion years old.

They were WRONG! Very Wrong.

Radiometric Dating - This is the technique that modern scientists use to estimate the age of the earth.

This technique uses the radioactive nature of rocks to calculate their age.

### Age and Time

Radiometric Dating uses the radioactive nature of rocks to calculate their age.

Some rocks contain isotopes - molecules with unstable nuclei, that give off particles at a constant rate (radioactive decay.)

Example:

An isotope has 7 particles in its nucleus on day 1.

On day 2 the isotope only has 6 particles.

On day 3 the isotope only has 5 particles.

### Age and Time

7 particles

5 particles

As particles leave the “parent element” it changes into a “daughter product.”

Half Life: The time over which 1/2 of the atoms of a radioactive isotope decay

Examples: The half life of Carbon-14 is 5730 years.

The half life of Uranium-235 is 740 Million years.

The half life of Potassium-40 is 1.3 Billion years.

### Age and TimeHalf life model:

14 particles

7 particles

Carbon-14.

Year 0:

Year 5730

Year 11460

Earth is believed to be between 4.5 and 4.6 Billion years old based on isotopes found in meteorites and in lead minerals in rocks.

3 and 1/2 particles