1. Absolute Dating

2. Bellwork
Someone tells you he is older than you – is this his relative or absolute age?
Someone tells you they are 25. Is this an relative or absolute age?
What is an atom
Draw a sketch of an atom and label the parts

3. EQ: how is the absolute age of rock measured?
SC.7.E.6.3
Objective:
Describe How Scientists measure the absolute age of rock layers using radiometric dating.

4. What is absolute dating?
absolute dating - Determining the age of an event or object in years.
Scientists often use radioactive isotopes to find the absolute age of rocks and other materials.
An isotope is an atom of an element that has a certain number of neutrons. 4

5. Quick review: What are atoms?
All matter is made up of ATOMS.
Rocks and fossils are made of atoms since they are types of matter.

6. atom review
Particles

7. Do all atoms look the same?
NO !!!
There are over 110 ways that atoms can look

8. What are radioactive isotopes?
Atoms in most elements are STABLE – they don’t change
some elements are UNSTABLE or RADIOACTIVE – they decay (or break down) over time.

9. What are radioactive isotopes?
Radioactive isotopes are isotopes that are unstable and break down into other isotopes. –
radioactive decay – During Radioactive Decay, atoms from one element break down to form atoms of another element.
Radioactive elements occur in rocks and organic matter

10. How do unstable elements decay?
Over time the atoms inside of the element give off:
Particles
Energy
This is called
RADIOACTIVE DECAY

11. Example : Carbon 14 is radioactive, it decays into Nitrogen 14.
Carbon 14 = the parent isotope
Nitrogen 14 = the daughter isotope

12. How fast do elements decay?
Each radioactive element decays at a constant speed. The speed never changes.
HALF-LIFE = the amount of time it takes for half of the radioactive element to decay into the new element.
After 1 half-life has passed Half (50%) of the parent isotope has changed into daughter isotopes.

13. Radioactive decay

14. After one half-life has passed, one-half of the parent isotope has changed into daughter isotopes.14

15. How fast do elements decay?
A given element will decay at a constant speed. The speed never changes.
This rate of decay is known as the element’s HALF-LIFE.
HALF-LIFE = the time it takes for half of the radioactive element to decay into the new element.

16. How do we use radiometric dating to determine absolute age
Scientists use many different isotopes for radiometric dating.
Determine the amount of radioactive element still left in the parent rock or fossil
Compare that with the amount of stable daughter element the radioactive element decays into.

17. How is radiometric dating used to date the age of the earth?
Igneous rocks. Cannot be used Because their birthdays are when the lava hardens.
Sedimentary rocks cannot be dated because they are made of old rocks. Their birthdays would not be right.

18. Why not Sedimentary Rocks?
Radioactive Dating would say these rock particles are 50 million years old
Radioactive Dating would say these rock particles are 100 million years old
Do you see the problem???
Let’s say this Sedimentary rock is actually 20 million years old.

19. How do we use radiometric dating to determine the age of the earth?
To find the age of the earth we use the age of Meteorites - small rocky bodies that travel through space and have fallen to earth’s surface. Radiometric dating on moon rocks and metiorites show that the solar system is about 4.6 billion years old

20. practice

21. Here are the elements used in radioactive dating

22. Radiocarbon Dating Carbon 14 decays to Nitrogen 14:
It is used to find ages of fossils, wood, and bone. All plants and animals contain Carbon 14 (radioactive element).
When an organism dies, the Carbon 14 starts to decay into Nitrogen 14 (stable element).
Half life is only 5730 years so you can only use it to date things that lived in the past years (otherwise the C-14 would all be gone)

23. If you find a bone in a layer of rock that is 500,000 years old could you use radiocarbon to find the absolute age of this bone? Why or why not

24. Potassium – Argon Dating
Potassium-40 to Argon
Useful for dating the older rocks because of the long half-life
It takes potassium (radioactive element) 1.3 billion years for half of it to turn into argon (stable element).
Can date things 100,000 yrs-billions of years old
Potassium
Argon
ROCK
Potassium
ROCK
1.3 billion years
(half-life)

25. Uranium-Lead Dating Uranium-228 decays to Lead-206
Used to determine age of igneous rocks
Half life of 4.5 billion years
For rocks 100,000 million years – a few billion years old. It cannot be used to find the age of younger rocks because not enough decays to measure.

26. Radiometric Dating
We can date the intrusion and extrusion and use their absolute ages to tell about how old the other layers are.

27. Exit
The breakdown of a radioactive isotope into a stable isotope is called _______________
______________ is the time needed for half of a sample of a radioactive isotope to break down to daughter isotopes
Name 3 methods of radiometric dating
Which of the following types of fossils can be dated using carbon-14? molds and casts, trace fossils, frozen in ice, asphalt. Explain your answer

28. exit
1. Describe the process of radioactive decay