 Look in your notes for the definition of half-life. Write it down.  You have 12g of radioactive material. How much material will be radioactive after 2 half-lives?  How much time has gone by if each half life is 2 hours?

 The amount of time it takes for ½ of a radioactive sample to decay.  12g after 1 half-life = 6g  After 2 half lives = 3g  After 2 half-lives, 4 hours would have gone by.

Parent Decay  Daughter Formation Curve Start 100 parents; 0 daughters 1 Half-Life 50 parents; 50 daughters 2 Half-Lives 25 parents; 75 daughters And so on… Total # of Atoms remains same

Radiometric Dating  Every radioactive isotope has a unique half-life  If you know how much radioactive material you start with, you can determine the age of the sample.  Two common isotopes  Carbon-14 Has half life of 5,730 years Used to detect up to about 60,000 years old  Uranium-238 Half-life = 4.5 billion years. Can detect the really old.

How much do you start with?  For C-14 dating, the object must have carbon in it.  There is always the same amount of C-14 in living things..  When you die, you stop getting this new C-14  For U-238 dating,  The object must have uranium in it… you get the idea

Practice If a sample contains an isotope with a half-life of 20,000 years, how old would the sample be if:  ½ the original isotope remain?  20,000 years  1/8 the original isotope remain?  60,000 years  What percent of the sample would be left if the sample was 40,000 years old? 25% (or ¼) Hint: Always start by figuring out how many half-lives there were.

 Worksheet  If you finish early there is a game online you can play. Check the SWIFT blog.

Radioactive dating game  Linked to my web page, or go to:  dating-game dating-game

WHOT 3/22  Dewium has a half-life of 5000 years.  When the sample was created it had 40g of radioactive material in it.  It now has 5g of radioactive material in it.  How long ago was this sample formed? Show all Work.

 Define Half-life  How many boxes should be shaded?  X-ed out?

 1. The amount of time it takes for ½ of a radioactive sample to decay.  2. a. 6 boxes (shaded), b. 3 boxes (x-ed).

3. At 25% K-40 remaining…  A. How many half-lives did it go through?  B. How old is the basalt?

 2 half-lives  2.6 billion years old.

4. Start with 100g, now 25g of C-14  How many half-lives?  How many years ago did the sample die?

 2 half-lives  11,460 years old

5. C-14 Sample is 17,190 years old.  A. How many half-lives did it go through?  B. What percent of the C-14 is left?

 3 half-lives  12.5% of sample left.

If a rock is 1.3 billion years old, using K-40 dating  A. How many half-lives did it go through?  B. What % of the K-40 would be left?

 1 half-life  50% left.

More practice.

WHOT 3/23.  Mooglium has a half-life of 100 years.  When the sample was created it had 80g of radioactive material in it.  It now has 5g of radioactive material in it.  How long ago was this sample formed? Show all Work.

3/24 WHOT Put these events in order from oldest to youngest. Now suppose Layer D has been dated at 400,000 years old. A large earthquake caused the fault (F) Make a statement about when the earthquake happened? F D E C B A

1 & 2 A.Shale and siltstone B.Volcanic Ash C.Basalt D.Limestone E.Sandstone F.Pegmatite G.Slate H.Granite A.Triceratops B.100 myo C.500 myo D.trilobites E.Unknown F.713 myo G.Bacteria H.1426 myo

3. A. The bacteria is between 713 and 1426 million years old. We haven’t aged the rock. B. between myo. There is an unknown layer. At least 100myo. You can be more precise because it is the newest layer.

1. Watch the HHMI short film The Day the Mesozoic Died. As you watch, pay attention to the key scientific evidence for or against the asteroid- impact hypothesis. 2. At the end of each act, your teacher will stop the film. You should pair up with your table partner and record the evidence and what the evidence means in the “Evidence of an Asteroid Impact” table at the end of this document. Each item should be no more than one or two lines in length. Also record the disciplines of the scientists mentioned in the film at the bottom of the table. To illustrate what is expected, the table has already been filled in with some pieces of evidence and what they mean.

3. After the film, be prepared to share with the class some of the facts you and your partner discussed and which ones you think represent the most critical pieces of evidence. Other students might have listed facts that you and your partner did not think of; add them to your list if you think they are relevant to the asteroid hypothesis. 4. After completing the table, answer the questions at the end of this worksheet.

History of life on Earth

Unconformity Break in the geologic record Frequently old layers of rock are eroded before new ones laid down

Relative Dating Exercises E (oldest) C B A D F (youngest) F D E C B A

Assignment

WHOT Q Missoula floods.

Relative Dating Practice.

Relative Dating Exercises Always start with the oldest rock and work toward the present. List the letters in order, with the oldest at the bottom T

Relative Dating Exercises F (Youngest) J B R Erosion A S M K P (oldest) T

Relative Dating Exercises Use colors to represent each layer

Relative Dating Exercises Yellow (youngest) Orange Brown Erosion N Folding A Green Blue Green Blue Red Green Blue Red Green (Oldest