This document discusses key concepts in geology including the difference between a timeline and timescale, relative and absolute dating, fossils, index fossils, rock layers, and unconformities. It explains that timelines show events in order while timescales assign numerical ages. Relative dating compares rock layers while absolute dating assigns numerical ages. Most fossils are preserved in sedimentary rock. Index fossils found in specific rock layers worldwide can help correlate rock sequences. The oldest rock layers are on the bottom according to the law of superposition, though layers can be disturbed by folding, faulting, or volcanic intrusions creating unconformities.

1. Relative Time
Fossils and rock layers

2. Remind me again…
What is the
difference
between a
timeLINE
and a
timeSCALE?

3. Remind me again…
What is the difference
between relative-age
dating and absolute-age
dating?

4. What is a fossil?
Fossil: The trace or
remains of an organism
that lived long ago.
 Are all organisms
preserved as fossils?
 There are three types
of rocks, do you
remember their
names?

Which type of
rock do you
think most
fossils are
preserved in?
Why?

5. If fossils are organisms of the
past, how can they help us tell
about the history of the earth?

6. Index Fossils

A fossil that is found in the
rock layers of only one
geologic age

They are found in rock
layers around the world

7. For example:
Which fossil is a good index
fossil?

9. Rock Layers

12. Almost one half
(approximately 2 billion
years) of earth’s history
can be seen at the Grand
Canyons National Parks
through the different rock
layers found there
It is one of the best places
in America to see this
much history

13. If you’re looking at a rock
sample, which layer would be
the oldest?

14. This is the law of SUPERPOSITION: in sedimentary rock
layers, the rocks are laid out fairly flat, where the oldest is on
the bottom and the youngest is on the top.

15. If nothing disturbs the rock layers they will
remain the same. If the rock layers are
disturbed, they may end up like this:

16. What things that can disturb rock layers?
•Folding or tilting from shifting plate tectonics
•Volcanic intrusions
•Faults

17. Volcanic Intrusions

18. Faults and plate tectonics

19. UNCONFORMITY
An unconformity is a gap in the
geologic record.
How could this happen?

20. Lets practice…

21. Lets practice…

22. How about a harder one?