Absolute Dating 8.3

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Text of Absolute Dating 8.3

  • 1. Absolute Dating Chapter 8, Section 3

2. Think About It . . . How old is Earth? What are some tools or methods that scientists could use to figure out the age of Earth? 3. Remember . . .

  • Geologists userelative datingto figure out if a rock is older or younger than another rock.
  • The older rocks are onbottom .
  • The younger rocks are ontop .

4. But What If You Want to Knowthe Exact Age?

  • Geologists often also need to know theexact ageof a rock or fossil.
  • Finding the exact age of an object is calledabsolute dating .
  • Remember absolute meansexactordefinite .

O 5. Atoms

  • Everything is made ofatoms .
  • Over time, some of these atoms maychangeinto adifferenttype of atom.
  • The original atom is called the parent .
  • The new form of the atom is called the daughter .

6.

  • Halfof theparentatomsturnintodaughteratoms once the object has reached a certainage .
  • Like howevery yearon your b-dayyouturnadifferentage .

Parents and Daughters 7. ParentsandDaughters

  • Scientists can learn the age of a rock bycountingthenumberofparentanddaughteratoms.
  • Like how I can learn your age bycountingthenumberof birthdays you have had.

8. Example

  • A scientist knows thathalfof theparentatoms will turn intodaughteratoms every 10,000 years.
  • Originally, there is16mgof parent atoms
  • 10,000 years go by . . .
  • Halfof the16mgof parent atoms turn into daughter atoms.
  • 16 2 =8
  • So there are8mgof daughter atomsnow
  • And there are8mgof parent atomsleft .
  • Check your math:8+8= 16 mg

9.

  • Then another 10,000 years go by . . .
  • Halfof the8mgof parent atoms turn into daughter atoms.
  • 8 2 =4
  • Now there are4mg moredaughter atoms.
  • Add this to the8mgthat has already formed
  • 8+4=12 mgof daughter atoms
  • And there are only4mgof parent atomsleft .
  • Check your math:12+4= 16 mg

Parent: 168 Daughter:08 10.

  • Then another 10,000 years go by . . .
  • Halfof the4mgof parent atoms turn into daughter atoms.
  • 4 2 =2
  • Now there are2mg moredaughter atoms.
  • Add this to the12mgthat has already formed
  • 12+2=14 mgof daughter atoms
  • And there are only2mgof parent atomsleft .
  • Check your math:14+2= 16 mg

Parent: 1684 Daughter:0812 11.

  • Scientists compare the number ofparentatoms to the number ofdaughteratoms.
  • The moredaughteratoms there are, the older the rock is.
  • This tells them how many times half theparentatoms turned intodaughteratoms.

12.

  • In this example, each time this happened,10,000 yearshad gone by.
  • So if it happened3 times , then the object is:
  • 3 x 10,000 = 30,000 yrs old

Parent: 168 4 2 Daughter:081214 13. Half-Life

  • Ahalf-lifeis the time needed for one-half of theparentatoms to turn intodaughteratoms.
  • Different atoms havedifferenthalf-lives.
  • Some have half-lives are more than 4 billion years; others have half-lives of only 6,000 years.
  • Scientists figure out which atom would be best to use to determine the exact age of a rock.

14. Half-Lives of Two Atoms

  • Potassium-40 has a half-life of1.3 billionyears. It can be used to date rocks older than 100,000 years.
  • Uranium-238 has a half life of4.5 billionyears. It can be used to date rocks older than 10 million years.

15. Age of Earth

  • Scientists have usedabsolute datingto figure out theage of the earth .
  • By counting theparentanddaughteratoms in some very old rocks, scientists say that the solar system (including Earth) is about4.6 billion years old !
  • (4,600,000,000 years old!)
  • Thats a lot of birthdays!
  • Before this method wasinvented, people believedEarth was only6,000yrs old.

16. Pop Quiz

  • 1) What method is used to figure out if a rock isolder or youngerthan other rocks?
  • RELATIVE DATING
  • 2) What methods has helped scientists determine theexact ageof Earth?
  • ABSOLUTE DATING
  • 3)Fill in thistable :

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