Do Now!Do Now!

1. 1. What are the 4 time units of the Geologic What are the 4 time units of the Geologic Time Scale from longest to shortest?Time Scale from longest to shortest?

2. What does the law of superposition state?2. What does the law of superposition state?

3. What does the principle of cross cutting 3. What does the principle of cross cutting state?state?

4. What concept states that the forces and 4. What concept states that the forces and processes that we observe today are the processes that we observe today are the same as they were in the past?same as they were in the past?

Radiometric DatingRadiometric Dating RadioactivityRadioactivity: The decay : The decay

((breakingbreaking apart) of an unstable apart) of an unstable isotope (nuclei) to a more stable isotope (nuclei) to a more stable isotope.isotope.

HalfHalf-Life: The time it takes for -Life: The time it takes for 5050% (1/2) of the nuclei in a % (1/2) of the nuclei in a radioactive sample to decay to radioactive sample to decay to its stable isotopeits stable isotope

Ex. Carbon-14 decays to carbon-Ex. Carbon-14 decays to carbon-12 (ALWAYS)12 (ALWAYS)

Radiometric DatingRadiometric Dating

RadiometricRadiometric Dating: Calculating Dating: Calculating the the ageage of rocks and minerals of rocks and minerals that contain certain radioactive that contain certain radioactive isotopes. isotopes.

Radiometric DatingRadiometric Dating

The fraction of original The fraction of original isotopesisotopes indicates the number of half-indicates the number of half-lives. lives.

Multiply the Multiply the numbernumber of half-lives of half-lives by the half-life by the half-life timetime to get the to get the age of the age of the fossilfossil..

Radiometric DatingRadiometric Dating

This method is possible because each This method is possible because each radioactive isotope has been radioactive isotope has been decayingdecaying at a at a CONSTANTCONSTANT rate since rate since the formation of rocks in which it the formation of rocks in which it occurs. occurs.

Cannot be used for Cannot be used for sedimentarysedimentary rocks because they are formed from rocks because they are formed from many pieces of many pieces of older older rocks. rocks.

FormativesFormatives

Work quietly and independently.Work quietly and independently.

When you complete your exam, raise When you complete your exam, raise your hand, and I will collect it.your hand, and I will collect it.

Begin silently and independently Begin silently and independently working on your radiometric dating working on your radiometric dating practice sheet.practice sheet.

*This is homework if you do not *This is homework if you do not complete it in class today.complete it in class today.

Exit TicketExit Ticket

1.1. What is radiometric dating?What is radiometric dating?

2.2. What is a half-life?What is a half-life?

3.3. How is radiometric dating used How is radiometric dating used to determine the age of a fossil?to determine the age of a fossil?