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 do scientists read rocks for an exact age?

Basic Atomic Structure  Electrons – orbit the nucleus.  Protons – are in the atom’s nucleus.  Neutrons - are in the atom’s nucleus. DO NOT COPY

I. Isotopes - the unstable form of an element (more neutrons than it should which makes it Radioactive) UNSTABLE STABLE

II. Radioactivity refers to energy and particles (neutrons) emitted from unstable isotopes. This process is known as Radioactive Decay. (makes the element stable) (Isotope)

III. Radioactive Decay Not affected by outside factors! Isotopes (unstable) decay into new stable elements. These Isotopes and their new elements are found in rocks and can be measured. -We call the Radioactive Isotopes, Parents. -Decayed elements are called Daughters.

IV. Using Radioactive Decay: (Radioactive dating, Radiometric Dating, Carbon dating, Absolute Dating) cover of your ESRT. - Knowing the rate of decay and the ratio of Parent Isotopes to Daughter elements, we can figure out how old the object is. A.Half – Life - time required for 50% of the Parent Isotopes to decay into daughter elements.

Which color dot represents the Parent elements? Which represents the Daughters?

V. 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)

If you can see in a rock sample there is 25% (1/4) C 14 and 75% (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.

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

What is the half life of Strontium 90? 25 years

22,8001/164 17,1001/83 11,4001/42 5,7001/21 01/10 Number of years % Parent Remaining Half-Life THE CHART THAT MAKES HALF-LIFE EASIER

Closure: Take out the worksheet you took from the back