Radioactive Dating

Open your notebooks to page 46 10.28.2014 Open your notebooks to page 46 Which type of dating is useful for dating young, once living things? What information can scientists gather form ice cores? What would keep scientists from using carbon dating on modern fossils? What 2 characteristic of fossils would make them good index fossils? Carbon 14 –Radioactive dating Information about climate changes from the past, and gases that were found in the atmosphere Nuclear bombs and nuclear activity interfers with carbon dating, so anything after 1940 can not be used for dating They have to be from a specific time period and found all over the world

Radioactive Decay…47 Used to find the absolute age The rate of decay is measured in half-lives. A half-life is the amount of time it takes for half of the atoms to change into another form.

2 Common Methods Uranium-238 Carbon -14 Half Life: 4.468 billion years Half Life: 5730 years Good for: Determining the age of the “younger” fossils Note: dating objects up to 40,000 years old Only works on things that were once alive (not rocks) Decays rapidly Uranium-238 Half Life: 4.468 billion years Good for: Determining the age of the “older” fossils Note: Used for dating older material (up to 4 billion years) Decays slowly

Parent material 50 % 75 % 87.5 % 93.75% 1st half life 2nd half life Daughter Material 50 % 75 % 87.5 % 93.75% 1st half life 2nd half life 50 % 3rd half life 25 % 4th half life 12.5 % 6.25 %

Carbon-14 has a half life of 5730 years If you find a fossil that has been through 3 half lives, how old is it? (5730 x 3 = 17,190)

ICE CORE Ice forms layers similar to that of rock Follows law of superposition Provides information about climate (thickness of ice layers) Analysis of the ice tells about the atmosphere (CO2, oxygen, volcanic ash) An ice core from Antarctica 3km long showed 740,000 years of history and 8 ice ages!!! ICE CORE