# 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 .

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.
• 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.
• 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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