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RAP 3/14 pg. 42 1.How old is the Earth? 2.How do we know?
RAP 3/14 pg. 42
1.How old is the Earth?2.How do we know?
TOPIC: Geologic History
29.1 Fossils29.2 Relative Time29.3 Absolute Time
Paleontology The study of life
that existed in prehistoric times
I. Fossils -Preserved remains or traces of once living organisms
1. Original Remains-preserved in its
entirety
Ex:
Wooly mammoths in ice and soilInsect in amber
A. Types
2. Replaced remains-Soft parts
replaced by minerals
Ex: Petrified wood
3. Molds and Casts-Mold: hollow depression
(cupcake pan)-Cast: copy of original fossil
(cupcake)
4. Trace-indirect evidence of
life
Ex: trailsfootprints
bite marksburrows
Trace fossilsAnd one more example...
coprolite
5. Carbonaceous Remains-thin carbon film
Ex. Fern print
What do we know about this animal?
Fossil FormationFossil formed? Type Why/Why not?
1
432
567
No not deep enoughYes Original Remains frozen
No too deepNo too much pressureYes replaced remains fused with minerals
Yes mould cast minerals filled in Yes trace uplifted
Fossil Formation Burying Bodies
Making Fossils
Who dung it?
RAP 3/15 pg. 421. What type of rock do most fossils
occur in?2. What is one method of preserving
a fossil?3. In the picture, which
letter represents the mold? Which letter represents the cast?
A B
II. Relative Time- placing events in the sequence in which they occurred
**Does not identify actual **dates
A. Principle of Uniform Processes
1. processes that occurred in past produce same results as today
B. Principle of Superposition Deposited sediments are
compressed into layers, or strata
1. Oldest layer at ; youngest at
bottomtop
Deciphering relative time is like detective work...
Who Dunnit?! Someone took the last cookie in the cookie jar last night.
The last person to leave is the culprit!
Clues: The Butler walks to work The Handyman rides a
bike The Cook rides a
motorcycle The Maid drives a car The Nephew has a
seeing-eye dog
1
3
2
Sequences on pg. 44
12
3
4
C. Principle of Cross-Cutting Relationships
1. intrusion is always than rock it intrudesIgneous younger
12
3
4
5
Gaps in Relative TimeD. Unconformity
1. indicates where layers of rock are missing
a. Exist because-Lack of deposition-Erosion
Example
1. Four characteristicsa. Easily recognizableb. Abundantc. Widespread in occurrenced. Existed only for a brief period
E. Index Fossils
When did I live?
Who’s On First?: Period 6 GroupsLab Table 1ShannonJakeJenny
Lab Table 2Chase Brice
Lab Table 3AlexDanielDylan S.
Lab Table 4Mitchell
Devin
Jordan C.
Kaitlin Bennett
Lab Table 5Davon
Ashtyn
Trey
Lab Table 6Josue
Yony
Ben
Luke
With Ms. RenwickGroup 7ChrissyKaitlyn BishopDylan WimerAnandhu
Group 8ZachRobertJordan B.
Put it all together... Decoding geologic history... And…
RAP 3/19 pg. 42 1. Select the fossil
you think would be the best index fossil and explain why.
2. Put the following events in the correct order.
A
D
CB
F. Correlation1. Matching of rock layers from one
area to another
Practice!
unconformity
Section 1 Section 2
Which layers are the same?Of layers E and F, which is oldest?What is the sequence of rock layer from oldest to youngest?An unconformity (buried erosional surface) is represented by the interface between which two layers?
III. Absolute TimeA. Use ACTUAL dates to order events
B. Methods1. Tree rings2. Varves- layer of sediment representing summer and winter
RAP 3/20 pg. 46
1. What is the difference between relative and absolute time?
2. What type of fossil shows evidence of an organism but not the organism itself?
RAP 3/21 pg. 46**QUIZ ON FOSSILS, Relative and Absolute Time1. What is the
relative age of layer C and D?
2. What two things can cause an unconformity?
3. Which letter to the right represents an unconformity?
3. Radiometric dating
Compares ratio of naturally occurring unstable isotope (parent) and its decay products (daughter)
Pb
Ur
Parent = original element Daughter = the product of the decay
• Example: uranium-238 decays to lead-206
i. Half-life-Time it takes for half the radioactive atoms to decay
=1 half-life
=2 half-lives
In each half-life, the amount of atoms gets cut in half.
=parent
=daughter
One half-life.
=parent
=daughter
Two half-lives.
=parent
=daughter
Three half-lives.
=parent
=daughter
Four half-lives.
=parent
=daughter
Don’t worry about the last atom. You start with so many trillions that you never really get there. (It will just decay and then they’re all gone.)
=parent
=daughter
About how many students would have had to sit down if we started with twice as many students? What about if we only had half as many in this class? What does that tell you about how the quantity of "radioactive isotopes" affects the number that decay?Can you predict which of you is going to be the first to sit down? Why or why not?
Keys to radioactivity **Decay at constant rates regardless of time or
climate** **Decay begins as soon as rock crystallizes or
organism dies** **Ratio of amount of radioactive element left to
the amount of stable product is used to determine the absolute age**
RAP 3/22 pg. 461. What is the definition of a half life?
Since you don’t know how many atoms you started with, a ratio between parent to daughter will tell you how many half-lives have gone by.
100% parent0% daughter0 half lives
One half-life.
50% parent50% daughter1 half-life
Two half-lives.
25% parent75% daughter2 half-lives
Three half-lives.
12.5% parent87.5% daughter3 half-lives
Four half-lives.
6.25% parent93.75% daughter4 half-lives
Half-lives range from a fraction of a second to billions of years• Protactinium-234 has
half-life of ~1 min• Uranium-238 has
half-life of 4.5 by
Radiocarbon limitations Only for once living organisms Half-life=5730 years meaning the limit to
dating is about 70,000 years
17190
RAP 3/14 pg. 451.
2.
3.
RAP 3/13 pg. 431. What is a half life?2. You find a piece of wood and use
carbon dating to determine the age. The ratio of parent to daughter is 1:1. How many half lives have passed?
3. How do varves help geologists understand the past?
Quiz Relative Time, Fossils and Absolute Time
Web quest
Let’s get a little more complicated…
