1. Geological Time - really, really, really long!
Motion pictures are generally projected at 32 frames per second. Therefore, each frame (image) is on the screen for only split second- let each frame represent 100 years.
Start movie at present and go back in time.
The Declaration of Independence would show up 1/16 of a second into the movie.
The Christian era (BC-AD boundary) would be 3/4 of a second into the movie.
The most recent Ice Age would be 7 seconds into it.
The movie would run about 6 hours before we got to the end of the Mesozoic era (extinction of the dinosaurs).
We'd have to watch the movie for about 2 days to see the beginning of the Paleozoic era (macroscopic life).
The whole movie (to the beginning of geologic time on Earth) would be approximately 16 days long!

3. Geologic Time • • Two ways to relate time in geology: > >
Relative
Relative
: Placing events in a
: Placing events in a
sequence based on their positions
sequence based on their positions
in the geologic record.
in the geologic record.
>
>
Chronologic
Chronologic
: Placing a specific
number of years on an event or rock
sample.
sample.

4. Geologic Time Scale • a combination of the two types of age
determinations
> a
relative
sequence of lithologic units -
established using logical principles
>
measured against a framework of
chronologic
dates.

5. Still being refined as more information becomes available
Geologic Time and the "geologic column"
Geologic Time and the "geologic column" • •
Developed using logical rules to establish
relative sequences of events
Developed using logical rules to establish relative
sequences of events - -
superposition - -
cross-cutting relationships - -
original horizontality - -
lateral continuity
Added to as new information is obtained and
data is refined • •
refined
Use of fossils for correlation and age determination - - • •
Numerical Dates attached to strata after the
development of Radiometric techniques - -
Still being refined as more information
becomes available

6. The Geologic Time Scale (1:2)

7. The Geologic Time Scale (2:2)

8. Relative Dating Methods•
determines the relative sequence of events.
>
which came first, which came last.
>
no numeric age assigned •
6 Relative age principles:
>
Superposition
>
Original Horizontality,
>
Lateral continuity
>
Cross-cutting Relationships
>
Inclusions
>
Fossil succession.
Those in yellow are most useful

10. Law of Superposition • •
In undisturbed strata, the layer on the bottom is
In undisturbed strata, the layer on the bottom is
oldest, those above are younger.
oldest, those above are younger.

11. Original Horizontality• •
Sediments are generally deposited as
horizontal layers.
Lateral Continuity • •
Sediment layers extend laterally in all
direction until they thin & pinch out as
they meet the edge of the depositional
basin.

12. included description and use of
Charles Lyell
Charles Lyell • •
1st Principles of Geology text - -
included description and use of
>
>
principles of cross-cutting relationships
principles of cross-cutting relationships
>
>
principles of inclusions
principles of inclusions • •
relative time tools
relative time tools

13. Cross-cutting Relationships
That which cuts through is younger than the
Object that is cut
dike cuts through
granite is cut

14. Relative Ages of Lava Flows and Sills

15. Principle of Inclusions•
Inclusions (one rock type contained in another rock type) are
older than the rock they are embedded in. That is, the younger
rock contains the inclusions

16. Principle of Inclusions

17. Faunal/Floral Succession• •
Fossil assemblages (groupings of fossils)
succeed one another through time.

18. relating rocks in one location to those in
• Correlation-
relating rocks in one location to those in
another using relative age stratigraphic
principles - -
Faunal Succession - -
Superposition
Lateral Continuity - - - -
Cross-cutting

19. Unconformities • • surfaces represent a long time. Hiatus
a time when rocks were not
deposited or
a time when rocks were
eroded
Hiatus
the gap in time represented
in the rocks by an uncon-
formity
3 kinds
Angular Unconformity
Nonconformity
Disconformity

20. Disconformities A surface of erosion or non-deposition between
Parallel sedimentary rock beds
of differing ages.

21. Angular Unconformities Angular Unconformities• An
angular unconformity
is an erosional surface on tilted
or folded strata, over which younger strata have been deposited.

22. Nonconformities A nonconformity is an erosional surface on igneous or
metamorphic rocks which are overlain by sedimentary rocks.

23. Breakout in to groups and discuss the sequence observed here

24. Age Estimates of Earth Counting lifetimes in the Bible
Comparing cooling rates of iron pellets.
Determine sedimentation rates & compare
Estimate age based on salinity of the ocean.
all age estimates were off by billions of years
some were more off than others!

25. Absolute Dating Methods
Radioactive
Decay sequences
acts as an atomic clock
we see the clock at the end of its cycle
analogous to starting a stopwatch
allows assignment of numerical dates to
rocks.
>
>
decay
) into
Radioactive isotopes change (
daughter isotopes at known rates.
rates vary with the isotope
e.g., U , K , C, etc. + +
235 40 14

26. unstable nuclei in parent isotope emits
Decay
unstable nuclei in parent isotope emits
subatomic particles and transform into
another isotopic element (daughter).
does so at a known rate, measured in the
lab
Half-life
The amount of time needed for one-half of a
radioactive parent to decay into daughter
isotope. •
Assumptions?-you bet
Cross-checks ensure validity of method.

27. Rate of Decay t All atoms are parent isotope or some1 3
All atoms are parent isotope or some
known ratio of parent to daughter
1 half-life period has elapsed, half of the
material has changed to a daughter
isotope (6 parent: 6 daughter) 2
2 half-lives elapsed, half of the parent
remaining is transformed into a daughter
isotope (3 parent: 9 daughter)
3 half-lives elapsed, half of the parent
isotope (1.5 parent: 10.5 daughter)
We would see the rock at this point.

28. 100 % parent remaining Parent Parent Daughter Daughter 50 25 13
Radioactive Isotopes
Radioactive Isotopes • •
analogous to sand in an hour glass
analogous to sand in an hour glass - -
we measure how much sand there is
we measure how much sand there is
>
>
represents the
represents the
mass of elements
mass of elements - -
we measure the ratio of sand in the bottom to sand in the top
we measure the ratio of sand in the bottom to sand in the top - -
at the end (present)
at the end (present)
>
>
daughter (b) and parent (t)
daughter (b) and parent (t) - -
we know at what rate the sand falls into the bottom
we know at what rate the sand falls into the bottom
>
>
the half life of the radioactive element
the half life of the radioactive element - -
how long would it take to get the amount sand in the observed
how long would it take to get the amount sand in the observed
ratio starting with all of it in the top?
ratio starting with all of it in the top?
100
Parent
Parent
% parent remaining
Daughter
Daughter 50 25 13
time >

29. Five Radioactive Isotope Pairs Five Radioactive Isotope Pairs
Effective
Dating Range
Minerals and
Isotopes
Half-Life
of Parent
(Years)
Rocks That Can
Parent
Daughter
(Years)
Be Dated
Uranium 238
Lead 206
4.5 billion
10 million to
Zircon
4.6 billion
Uraninite
Uranium 235
Lead 207
704 million
Muscovite
Thorium 232
Lead 208
14 billion
48.8 billion
Biotite
Potassium feldspar
Rubidium 87
Strontium 87
4.6 billion
10 million to
Whole metamorphic
4.6 billion
or igneous rock
Potassium 40
Argon 40
1.3 billion
100,000 to
Glauconite
4.6 billion
Muscovite
Biotite
Hornblende
Whole volcanic rock

30. Carbon-14 dating is based on the Carbon-14 dating is based on the
Radiocarbon and Tree-
Ring Dating Methods
Carbon-14 dating is based on the
Carbon-14 dating is based on the • •
ratio of C-14 to C-12
ratio of C-14 to C-12
in an organic
sample.
sample.
>
>
Valid only for samples less than 70,000
Valid only for samples less than 70,000
years old.
years old.
>
>
Living things take in both isotopes of
Living things take in both isotopes of
carbon.
carbon.
>
>
When the organism dies, the "clock" starts.
When the organism dies, the "clock" starts.
Method can be validated by cross-checking with tree rings

31. Carbon 14 Cycle