Transcript Rock Notes

Dating Rocks!
Figure 7
How old is stuff?
• Law of superposition:
•Gives relative age of fossils/rock based on
it’s depth.
The Law of Superposition
 Relative Age – age compared to rocks above or
below.
 If rock layers are undisturbed, younger rocks lie
above older rocks and the oldest rocks are at the
bottom.
Index Fossils and Relative Dating
 Relative Age
 Examine fossils found in them
 Index fossils – you know the fossil age, so assume
the rock formed during the same time the organism
lived.
Figure 7
How old is stuff?
•Index fossils:
•Common fossils that occurred over a large
area – can be used to determine the relative
age of rock.
Figure 7
How old is stuff?
•Radioactive dating:
•Determines the absolute age of rock or fossil
•It is the amount of time that has passed
since it was formed…looking at half-life.
Radioactive Dating
 Absolute Age – time passed since the rock formed.
 Common radioisotope used: potassium-40 (1/2 life
of 1.3 billion years)
 Read/Skim pages 732-734
 Using complete sentences answer
the following questions found on
page 738:
1, 2, 6, 7, 8, 9