Module 3 Assignment Geologic Time-1
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University of Texas, Permian Basin *
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1301
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Geology
Date
Feb 20, 2024
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docx
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Uploaded by JudgeSnowEagle23
1
Module Assignment– 3: Geologic Time
(40pts)
In this module assignment you will identify and use relative age dating principles and
rock relationships and reconstruct parts of geologic history using rock strata and fossils. You will calculate the absolute ages of layers utilizing index fossils and isotopic half-life ages. This laboratory evaluates your understanding of deep time and how it is computed.
Deep Time
Geologic Time
is vast. It is hard to wrap the human mind around 4.5 billion years ago. We humans have only been living on earth for about 0.0003% of geologic time, making our existence here rather unimportant in terms of “deep time”. To better comprehend this enormous time scale, geologist use metaphors to illustrate the history of our dynamic planet. Before understanding geologic time, remember geologists measure events on the planet in years before present, and use “Ka” to represent 1,000 years and “Ma” to represent one million years, and “Ga”, for one billion years. Imagine this calendar below is the framework of the entirety of earth’s history. Circle the dates on the calendar on the next page. A few have been done for you.
Origin of the solar system and Earth: January 1
st
Formation of the moon: January 4
th
Oldest mineral grain (zircon, 4.4 Ga) : January 12th
Oldest rock (Acasta Gneiss, 4.0 Ga): February 13th
Oldest evidence (chemical) for life (3.8 Ga) : March 1st
Oldest known fossil evidence (bacteria, 3.5 Ga): March 25
th
Oldest animal fossils (600 Ma): November 13
th
Oldest terrestrial fungi (440 Ma): November 26th
Worst mass extinction (there have been at least five large mass extinctions):
December 11
th
Oldest known mammal fossils (180 Ma): December 17th
Extinction of the dinosaurs (65 Ma): December 26th
Humans: December 31
st
o
12:25 Humans and chimpanzees lineage diverge (6 Ma)
o
11:25 Origin of Homo sapiens (300,000 years ago)
o
11:58 Domestication of the dog (14,700 years ago)
o 11:59 PM
22 seconds the oldest writing (5,518 years ago)
29 seconds the Great Pyramid of Giza was built (4,578 years ago)
57 seconds the Roman Empire
59 seconds the last 150 years or post-Industrial Revolution
Please provide all written answers in bold if you are typing so they are clear and easy to read.
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3
Figure 3.1
9. What type of uniformities is
B (Fig. 3.2)?
Disconformity
10.
What type of unconformity
is A (Fig. 3.2)?
Nonconformity
Figure
3.2
List the following letters of geologic layers or structures from youngest to oldest from Figure 3.1. There is one unconformity and one fault.
1.A
2.D
3.C
4.B
5.E
6.F
7.G
8.H
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4
Absolute Time
On the next page is a blank half-life graph, follow the directions to first to create a complete graph and then use it to calculate absolute ages. (
5pts)
11. Draw over neatly in red the parent percentage curve. Note: This curve is
exponential. It decreases by a half, every interval or half-life. There are four
intervals on this particular graph.
12. Label the four intervals, T1, T2, T3, T4, T5 on the x-axis. These represent the half-
lives.
13. Label the y-axis. This is the percentage; label 50, 25, 12.5, 6.35.
14. At the point on the graph where the two indices meet to create a point and write:
a.
write ½ where 50% and T1 meet
b.
write ¼ where 25% and T2 meet
c.
write 1/8 where 12.5% and T3 meet
d.
write 1/16 where 6.25 and 4T meet
15. Draw in blue of the approximate curve of daughter percentage atoms on the half-
life graph (hint: this should mirror the parents curve).
Calculate the ages of the metamorphic and igneous layers using their parent to daughter
atom ratios. You will need resources from the online access point from Kendall Hunt to do calculations.
16. A mineral sample from rock unit B has 150,000 atoms of uranium-235 and 50,000 atoms of lead-207. The age of the rock is:
17. A mineral sample from rock unit C has 50,000 atoms of uranium-235 and 150,000 atoms of lead-207.
The age of the rock is:
18. A mineral sample from rock unit G has 100,000 atoms of potassium-40 and 100,000 atoms of argon-40. The age of the rock is:
Example to calculate:
I.
Get the percentage of parent isotope remaining (c) by taking parent atoms divided by the total of the parent plus
the daughter atoms. (
a/a+b=c
)
a.
parent atoms
b.
daughter atoms
c.
percent of parent isotope remaining
II.
Go to Half-life Graph and use the Y axis (% of parent isotope remaining which is variable c above) to then move across and down using the figure to collect the correct number of half-lives at the X axis which corresponds to the % remaining. (e.g., 2 half-lives)
III.
To calculate the time or absolute date for each of the igneous or metamorphic rock layers:
a.
Multiply the half-life value from X axis (e.g., 2 half-lives) with the number of Half- Life in Years (
Common
isotope elemental pairs chart
) for those isotope series (e.g., uranium-235 decays to Lead-207 in
704,000,000 years)
b.
Time=half-lives * isotope half-life in years
c.
Time = 2*704,000,000 million years ago
d.
=1,408,000,000 or 140.8 million years ago
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Half-Life Graph
© MilanB/Shutterstock.com
6
Relative Time
List the following letters of geologic layers or structures from youngest to oldest in Figure 3.3
.
19.A
20.H
21.C
22.D
23.D
25.F
26.I
Figure 3.3
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Index Fossils
Refer to your Fossil Chart. These layers are the layers illustrated and labeled in Figure 3.3. Note: mya = millions of years ago
27.This fossil was found in Layer A:
Layer A was formed 2.58___
mya during the _quartenary______
Period.
28.This fossil was found in Layer B
: Layer D was formed 251.9___
mya during the _triassic_____
Period.
29.This fossil was found in Layer D
: Layer D was formed 358.9___
mya during the Caboniferous_______
Period.
30.This fossil was found in Layer E
: Layer E was formed 485.4___
mya during the _Ordovician_____
Period.
31.The following fossils were found in Layer F:
Layer F was formed
485.4__________
mya during the________Devonian_____
Period.
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32.
What is the least amount of time that could have passed during the hiatus represented by youngest unconformity seen in Figure 3.3?
150.4 million years
33.
What is the least amount of time that could have passed during the hiatus represented by the older unconformity seen in Figure 3.3?
708 million years
34.
A geologist finds this outcrop in the field and take photos, a GPS point, descriptions, and samples of the green and black rocks in the image below. The geologists brings back the samples to the laboratory. Using geochemical data, the geologist concludes the rocks are different in composition and one is much younger than the other. The green rock is olivine, and the black is basalt. Which of the rocks is older? Why?
(2pts)
basalt would be older. It is older because the Olivine formed inside basalt which was there first
35.What is the name of this principle?
The law of superposition
36.Why can’t
radiometric dating used to determine the age of sedimentary rocks? (2pts)
Because the radiometric elements will decay the sedimentary rocks
37.
How have fossils contributed to the organization of the geologic time scale? (2 pts)
The species found inside the fossil help determine time because the can tell the beginning and ending of ages because of the species
SergeyVIvanov/Shutterstock.com