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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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Table of contents

Table of Contents

  • Titles: Age and Time

    • Page #: 13

    • Date: 9/12/12


Objective

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

Words of the Day

  • 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 time age of earth

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

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 time1

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 time half life model

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


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