1. Table of Contents Titles: Age and Time Page #: 13 Date: 9/12/12

2. 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.

3. 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.

4. Age and Time Age 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.

5. 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.

6. Age and Time 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. 7 particles 5 particles

7. Age and Time Half life model: 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. 14 particles 7 particles 3 and 1/2 particles