Do Now: Think about this… If you were standing 10 feet from the wall, and I asked you to walk half the distance to the wall, how close would you be? If I asked you to repeat this process, would you ever reach the wall? Aim: How can the decay of an organism tell us its age?

Basic Atomic Structure  Electrons – Orbit the nucleus (negative electrical charges).  Atomic number is the number of protons in the atom’s nucleus.  Mass number is the number of protons plus neutrons in an atom’s nucleus. DO NOT COPY

I. Isotopes - the unstable form of an element. - The atoms have the same number of protons and different number of neutrons.

EXAMPLE Stable Element, Carbon-12: -6 Protons -6 Neutrons Unstable Element (Isotope), Carbon-14: -6 Protons -8 Neutrons DO NOT COPY

II. Radioactivity refers to energy and particles emitted from unstable isotopes. This is known as radioactive decay (Isotope)

III. Absolute Age : (Radioactive dating) - Using precise numbers to tell when an organism lived or an event occurred. - This can be done by using radioactive isotopes. cover of your ESRT.

IV. Radioactive Decay Continues at a regular rate (not affected by outside factors). The first isotope is called the parent nuclei. (unstable) When it decays, it turns into the daughter nuclei. (stable isotope)

A. Half – Life: - time required for half of the atoms in a sample of radioactive element to decay. **The parent nuclei (Red) changes to the daughter nuclei (Blue)

V. Dating with Carbon-14 -Used to date most recent organic material. (organisms and plants) -Shortest half-life. -Found in people

Examples: Use your ESRT How many years will it take for two half- lives to pass of C14? What % of C14 will remain at this point? Which isotope has the longest half life? What is it? 11,400 yrs 25% C14 will remain Rubidium-87 ( 87 Rb)

Example 1: Use your ESRT If you can see in a rock sample there is 1/4 C 14 and 3/4 N 14, the sample must have gone through how many half-lives? Two half-lives. How old is this sample? 11,400 yrs old.

EXAMPLE A student found a fossil and by looking at the radioactive decay of C14 she found there to be 1/16 th of C 14 remaining in the fossil. How many half lives has this sample gone through? The sample has gone through 4 half- lives

22,8001/164 17,1001/83 11,4001/42 5,7001/21 01/10 Number of years % Parent Remaining Half-Life

Closure: Obtain the worksheet form the back, we are going to work on it together.