Warm-Up 11/15 1.What is an index fossil? 2.How are fossils relevant to your daily life? 3.What are some limitations of relative dating? 4.What is radiation?

TO THE LIBRARY! Walk to library in an orderly and quiet fashion! 10 min to pick out a book 5 min to read Return to class in a quiet and orderly fashion! I have a lab planned for today that we can only get to if we don’t waste time! Worksheets are back-up plans!

1.What is a parent atom? 2.What is a daughter atom? 3.What is a half life? 4.If you have 10 grams of a radioactive element how many grams of that element will you have after one half life? Warm-Up 11/16 WARM-UPS DUE TODAY! TURN IN AFTER NOTES.

Absolute Dating Absolute dating is simply the actual age of a rock layer. The 3 ways of absolute dating we will examine are: Varve count, radioactive decay/half-life, and carbon dating.

1. Varve Count Sort of like counting the rings in a tree trunk to determine tree age. Varves: annual layer of sedimentary deposit on a lake bed. Usually a glacial lake. Sediments are brought in during summer and settle during winter, giving a yearly ring, just like the rings on a tree trunk.

True or False… Varve count can be compared to rings in a tree trunk.

True or False… Varves are usually found in glacial lakes.

2. Radioactive Decay Radioactive elements  unstable elements Unstable means the elements break down into isotopes to try and become stable. Once they reach a stable state this isotope is called the daughter element.

True or False… The stable isotope is referred to as the “sister” element.

2. Radioactive Decay Con’t Example of radioactive decay of an element: U-238  emits 2 protons and 2 neutrons Th-234  one neutron changes into a proton and an electron then electron is emitted Pa-234  still unstable, energy is emitted Pb-206  finally reach daughter element

2. Half-life Refer back to previous example…Let’s pretend we started with 10 grams of U Scientists have found a way to calculate the length of time that it takes for HALF of that amount to radioactively decay to Pb-206 (daughter element)

2. Half-life Con’t Half-life: the time it takes for HALF the mass of a given amount of a radioactive element to decay into its daughter element.

True or False… For a half-life to exist in an element the element must be radioactive.

3. Carbon Dating A common isotope of Carbon is C-14. We know the half-life of this isotope is about 5,730 yrs. C-14 is present in CO2(Carbon Dioxide) which means all things exposed to CO2 will have some amount of C-14 in them. We use C-14 and our knowledge of C-14’s half-life to determine approximate age

True or False… The half-life of C-14 is about 3,750 years.