1. The actual age of a fossil or rock formation
Absolute Age
The actual age of a fossil or rock formation

2. The smallest unit of matter that makes up everything on Earth.
What are atoms?
The smallest unit of matter that makes up everything on Earth.
What are elements?
Matter that is made up of the same atoms.

3. What is a radioactive element?
The atoms of many elements exist in different forms.
Most of these forms are stable and do not change.
But some of these forms are said to be unstable elements.
It’s these unstable elements that are called radioactive.

4. What are some examples of radioactive elements?
Carbon -12 (stable): Carbon-14 (unstable)
Potassium – 39 (stable) : Potassium-40 (unstable)

5. What is radioactive decay?
Radioactive (unstable) elements want to be stable.
The unstable element (parent material) breaks down to become another element (daughter material).
This is called RADIOACTIVE DECAY

7. What is radioactive dating?
Radioactive dating is how scientists use radioactive elements to determine the absolute age of fossils & rocks.

8. Why are radioactive elements used to determine the absolute age?
The radioactive decay always happens at the same rate (speed).
If you know how fast it breaks down, then you can figure out how much time has passed by.

9. What is a half-life?
The amount of time it takes for half of the radioactive atoms (unstable atoms) to change into a stable element.
Different radioactive elements have different half-lives.

10. What are some examples of radioactive elements’ half-lives?
Carbon-14 –changes into Nitrogen-14
half-life of 5,730 yrs
Potassium-40 – changes into Argon-40
Half-life of 1.3 billion yrs
Urianium-235– eventually changes into Lead-207
Half-life of 704 million yrs
Urianium-238– eventually changes into Lead-206
Half-life of 4.5 billion yrs

12. Half-life Example The half-life of C-14 is about 5700 years.
(Every 5700 years, HALF of the C-14 changes!)
You have 60 grams of Carbon-14.
After 5700 years pass, how much C-14 would you have? N-14?
Now you have 30g of C-14 & 30g of N-14
Another 5700 years go by.
How much C-14 would you have? N-14?
15g of C-14 & 45g of N-14
This would continue until all the unstable element becomes stable.

13. How is absolute age found from radioactive dating?
In radioactive dating, scientists first find out how much radioactive element is in the sample.
Then, they compare the radioactive amount to the stable amount.
The ratio between stable and unstable lets scientists know how many half-lives the fossil or rock has gone through, and therefore, how old they are.

14. YouTube:
Carbon Dating

15. Radioactive dating can only be used on what?
Absolute age can only be determined for igneous rocks
Any fossils that have some organic parts remaining
for example: original remains, carbon film, bones that are only partially petrified.

16. When does radioactive decay begin?
In non-living things, radioactive decay starts as soon as the magma or lava hardens. OR
In living things, every time an organism dies a stopwatch starts ticking.
Death starts the stopwatch.
Science can read it.

17. Why can’t we find the absolute age of sedimentary rocks or of fossils made from sediments?
Sedimentary rocks and fossils made from sediments are formed from millions of pieces of particles that come from rocks of all different ages.
Radioactive dating would find the ages of the particles not the age of the whole rock.
We’d never know how old the rock really is!

18. How do scientists date sedimentary rocks?
To date sedimentary rocks, scientists find the age of any intrusions or extrusions that are near the sedimentary rock.
So, any layer of sedimentary rock above an intrusion or extrusion, is YOUNGER! Any sedimentary layer found below an extrusion is older.
(RELATIVE AGE!!!)

19. How old is the Earth?
The oldest rocks ever found on the Earth have been dated at about 4.0 billion years old, but scientists believe the Earth is really…
4.6 billion years old.

20. How do we know how old the Earth is?
Scientist believe the Earth and the moon formed at the same time.
Scientist have dated moon rock brought back to Earth by astronauts.
Therefore the Earth is believed to be at least as old as the moon rocks.