5. What is Dating?
When geologists date rocks, they are
determining how long ago they were
formed.
Two ways to do this:
Relative Dating
Absolute Dating
6. Relative Dating
Determining how old
something is
compared to
something else
Use words like
“older” or “younger”
instead of exact
numbers
7. I. Relative Dating
Relative Dating is
when you give the
age of a rock or
fossil compared to
another rock or
fossil.
Example: Rock A is
OLDER than Rock B.
An actual age in years
is not determined.
8. II. Rules of Relative Dating
1. Law of Superposition: When sedimentary
rock layers are deposited, younger layers
are on top of older deposits.
9. Rules of Relative Dating
2. Law of Original Horizontality: Sedimentary
rock layers are deposited horizontally. If
they are tilted, folded, or broken, it
happened later.
10. Rules of Relative Dating
3. Law of Cross-Cutting Relationships: If an
igneous intrusion or a fault cuts through
existing rocks, the intrusion/fault is
YOUNGER than the rock it cuts through
15. Absolute Dating
Determines the specific age of a fossil
Looks at chemical properties
2 types:
Carbon-14 (radiocarbon)
Potassium-Argon
16. Carbon-14 Dating
Also known as Radiocarbon dating
Used to date organic substances
Scientists measure the radiocarbon in the
fossil to determine its age
Can only date specimens up to about
60,000 years old
17. Potassium-Argon Dating
Scientists determine the age of the rock
surrounding the fossil to determine the
fossil’s age.
Used only for inorganic substances (rocks
and minerals)
Scientists measure the amount of argon in
the rock to determine its age
Dates rock 60,000 years old and older
18. How Absolute Dating Works
When magma/lava cools, radioactive elements
are incorporated into the minerals
Examples:
-- Potassium 40
-- Uranium 235
19. How Absolute Dating Works
These elements begin to decay at a known rate
starting when the rock cools
We can measure how much of the element is
left
Tells us how much time has passed since the
rock formed.
20.
21. What can we learn from this?
T-Rex Fossil
Geologist
Basalt, dated to 80
mya
Basalt flow, dated
to 100 mya
Sandstone
So when did this T-Rex live?
Between 100 and 80 mya
This may not seem very accurate, but compared to
the 4,500 million years the earth has been around it
gives us a lot more information than we had before
22. What can we learn from this?
Absolute Dating
Helps us determine the age of the earth
Helps us determine when specific events in the
history of the earth happened (ex. Extinction of
the dinosaurs)
Relative Dating
Can help us estimate the time span between
major earthquakes, storms, tsunamis etc
Can help us determine the order that life forms
developed on earth
26. If you wanted to figure out the
exact age of a rock, what
technique would you use?
a.Relative Dating
b.Carbon-14 Dating
c.Law of Superposition
d.Potassium-Argon Dating
27. If you were looking to find the
exact age of a fossil that is at
least 1 million years old, what
technique would you use?
a. Carbon-14 Dating
b. Potassium-Argon Dating
c. Relative Dating
d. You can’t; it is impossible
28. If you wanted to figure out the
exact age of a fossil that is less
than 40,000 years old, what
technique would you use?
a. Carbon-14 Dating
b. Potassium-Argon Dating
c. Relative Dating
d. You can’t; it is impossible