 Hand in any work needed.  Get out a small piece of paper, PUT YOUR NAME ON IT.  When bell rings the quiz will start and you will have 1 minute per question to answer.

 When were the earliest birds?

 When did dinosaurs go extinct?

 Give me the LAT/LONG of Old Forge and what kind of fossils are there?

 When was the “peak development of eurypterids”

 1.) When were the earliest birds? Jurassic  2.) When did dinosaurs go extinct? 65 MYA  3.) Give me the LAT/LONG of Old Forge  and what kind of fossils are there?  43 o 45’ N 74 o 45’ W no fossils  4.) When was the “peak development of eurypterids”  Silurian

 Radiometric isotope (parent isotope) The original element.  Daughter isotope The new element after decay.  Half-life

 What is this?  Radioactive decay means to: Break down over time.  Certain elements decay over time. They release electrons which changes element.  By looking at what and how much of an element there is, you now how old it is.

2 half lives 1 half life 0 half life 100% Carbon 14 50% Carbon 14 25% Carbon 14 25% Nitrogen 14 50% Nitrogen 14 50% Nitrogen 14

 A half life is how long it takes for ½ (50%) of the amount to decay into its daughter isotope.

 Carbon (C) good for short time periods. Thousands of years. Dates humans, things from last ice age.  Potassium (K) good for long periods millions of years  Uranium (U) good for long terms millions of years. Oldest rocks on Earth.

 All elements will decay over time. Eventually there will be so little left that it cannot be dated.  After 175 years there is less than 1% left of the original.  All elements graphs look the same!

 Carbon (half live = 5700 years) so, ½ the amount is left after 5700 years, ¼ the amount is left after 5700 x 2 = years 1/8 the amount is left after 5700 x 3 = years

Try this:  If I start with 100 grams of sugar. And I know that sugars half life is 2 years.  So in 2 years I will have 50 grams of sugar left…  In 4 year I have  In 6 years I have Every 2 years is one half life, so how many did I go through here? OR

3 half lives 2 half lives 1 half life 0 half life 100% Sugar 50% Sugar 25% Sugar 25% 50% 12.5%25%50% 12.5% Sugar 2 Years4 Years6 Years

 How many half lives did the element carbon go through if there is only 6.25g left of the original sample of 100g? 100 -> 50 -> 25 -> > 6.25 So, 4 half lives

 How long does it take Carbon-14 to decay 2 half lives?  One HL = 5.7 x10 3 years or 5700 years  Two HL = (5700 x 2) 11,400 years  And so on..

 Uranium-238 is taken from a rock. It is found to be 10g. Over 5 Half lives what was the original amount and how old is it?  DRAW IT OUT ON CHART!! First, HL of U-238 is 4.5x 10 9 years or 4,500,000,000 years. How many half lives are there needed? 55  (5 times 4,500,000,000) 2.25x10 10 or 22,500,000,000 years 10 -> 20 -> 40 -> 80 -> 160 -> 320 grams started