Laboratory Exercise: Geologic Time

Name __________________________________________ ESC 101
Laboratory Exercise: Geologic Time
Part A: Understanding Geologic Time.
As you learn about past events in Earth history you may be surprised when you hear that something occurred
“only” a million years ago. In the context of a human lifetime this is an enormous amount of time. Yet, geologists may
consider this to be a short time ago when compared to Earth’s age. The enormity of geologic time is difficult to
understand. One way to help visualize geologic time is to create a time-line.
To illustrate the enormity of geologic time the length of football field will be used as a time-line for geologic
events (Figure 1). Because distances in American football are measured in yards, this analogy will not use metric units of
measure.
The present will be placed on the goal line near the “Geologists” end zone. As we move away from the goal line
towards the “Astronomers” end zone we are moving further into the past. As you move back towards the “Geologists”
goal line you are moving closer to the present. On this scale, one yard is equal to 46 million years. Using this scale the
estimated time of origin of Earth and solar system (4.6 billion years) is 100 yards away, at the “Astronomers” goal line.
You can see that on this scale the extinction of the dinosaurs occurred only 1.4 yards from the present (the “Geologists”
goal line). It must be noted that many scientists believe that not all dinosaurs became extinct. There is evidence that
birds are the last surviving branch of the dinosaurs! Earliest humans lived 2.4 million years ago. This would be only
0.05 yards (1.8 inches) from the present. This illustrates that even a million years isn’t a long time in terms of Earth’s
age. On this scale the length of a football field from goal line to goal line is equal to the entire time Earth has existed.
One million years is equal to only 0.7 inches!
Figure 1: Geologic Time-Line © Brian Vorwald (2009)
ESC 101: Professor Vorwald Geologic Time Page 1 of 6

Part A: Understanding the Geologic Time Scale
In Laboratory One in your lab manual read the section, Part 1A on pages 2 and 3, up to the section titled, “Processes and
Cycles of Change.” Also study the Geologic Time Scale, Figure 1.3 on page 4. All Earth history has been organized into
what is called the geologic time scale, which like a calendar. In this calendar we can refer to many events and rock units.
As in a calendar, the geologic time scale has subdivisions with longer time periods being broken into smaller time
periods. The basis for these subdivisions is the fossil record and extinctions.
1. The Precambrian the an informal name for geologic time from Earth’s origin up to 542 million years ago.
a. List the names of the eons that comprise the Precambrian, starting with the oldest eon.
____________________ ___________________ ____________________
Age decreases (closer to the present)
b. The graph below (Figure 2) represents the percentage of time for each of the major eons.
Figure 2 - The Eons of Geologic Time
Find the percent of total Earth History represented by the geologic time units using the directions listed
below. Record your answers in Table 1.
# The angular measure of each time interval in the pie graph has been determined and is listed in
Table 1.
# Find the percentage of the circle for each eon using the following equation:
Percentage = Measured Angle in degrees X 100
360 degrees
Table 1
Time Unit Measured Angle Calculations Percent
Cenozoic Era 5 o
Mesozoic Era 14 o
Paleozoic Era
22 o
Precambrian Eon 319 o
c. Explain why Geologic Time Scale shown in Figure 1.3 is not accurately constructed.
ESC 101: Professor Vorwald Geologic Time Page 2 of 6

2. Which is the largest subdivision of time? (Eon, era, period, epoch)
3. What is the name for the oldest eon? _____________________________
4. List the periods of the Mesozoic Era starting with the oldest period. _____________________________
5. Which period ended 416 Ma?
6. Which period started 200 Ma?
7. Eons, eras, periods, and epochs of time are used to group events and relationships of geologic time. What do
enothems, erathems, systems, and series rock represent?
________________________________________________________________________________________
8. Determine the total duration of time for the Paleozoic Era. ____________________
Show work here
9. Based on Table 1 and Figure 1.3, what percentage of Earth history is well documented by fossils? _______ %
Show work here
Part B: Historical Time Grid Model for Geologic Time
Figure 3 is a grid representing the last millennium. In this model, you will determine how many pieces of paper, each
representing 1,000 years it would take to represent all of Earth history. Then if you were to place each piece of paper
representing 1,000 years of Earth history one on top of the other, you will find how high the stack of paper would be.
1. On the “Historical Time Grid”, each box represents one year and the entire grid represents 1,000 years.
# Plot each of the historical events listed in Table 2 on the gridsheet by placing an X in the appropriate box.
# Note that the millennium starts with the year 1001 and the box is labeled with an S. The millennium ends
with 2000 (labeled with an E). When determining the date for each box count from right to left.
Table 2
Column 1 Column 2
Date Event Date Event
Your birth date 1776 Declaration of Independence signed
1976 Viking I land on Mars 1620 Pilgrims land in New England
1969 First Men landed on the Moon 1453 Hundred Years War ended
1963 President John F. Kennedy Assassinated 1337 Hundred Years War began
1945 End of World War II 1215 Magna Carta signed
1918 End of World War I 1095 Pope Urban II called for the Crusades
1865 End of the Civil War 1066 William of Normandy conquered England
2. The height of gridsheets stacked one on another for selected events
Table 3 shows several important geologic events. Because they will not fit on one gridsheet, it will be necessary
to calculate the number of gridsheets that will represent the number of years before the present for each event
using the following steps. Record all data in Table 3.
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a. Determine the number of gridsheets for each event. Since one gridsheet represents 1,000 years divide the
number of years by 1,000.
b. Paper Height: Because the thickness of each piece of paper is so small, we will measure the paper height
using reams (packages) of paper. Each ream has 500 gridsheets and is 5.0 cm thick.
# Determine how many reams of paper would be needed for each event by dividing the number of
gridsheets by 500.
# Find the height of the reams by multiplying the number of reams by 5.
# Convert the ream height to meters. Since one meter is equal to 100 cm, divide the height in
centimeters by 100.
Table 3
Events Time in
Years Before
the Present
Farthest advance of last glacial ice 22,000
st 1 Pleistocene glacial advance 1,000,000
First ancestral human, Homo
Habilis (First member of the genus
Homo)
Extinction of “non-avian”
dinosaurs
2,400,000
65,000,000
Earliest Dinosaurs 232,000,000
Beginning of Cambrian Period 544,000,000
Oldest rocks found on Earth 4,280,000,000
Age of Earth 4,600,000,000
Number of
Gridsheets
Reams
of Paper
Ream Height
centimeters meters
Questions:
1. For about what percent of Earth’s total history have humans (represented by the genus Homo) been in
existence. Show your calculations below.
_________ %
2. Compare Earth’s age to the age of the oldest Earth rocks found.
3. How many reams of paper would be needed for the total time non-avian dinosaurs _______reams
existed on Earth? Show your calculations below.
4. How does the existence of humans compare with Earth’s age?
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E
Historical Time Grid
From Explorations in Earth Science by Osmun R, Vorwald B, and Wegner S., UPCO: ©2007.
Preprinted with permission
ESC 101: Professor Vorwald Geologic Time Page 5 of 6
S

Part C: Radiometric Dating
Complete Activity 8.3 in Laboratory Eight of your laboratory manual. It is found on page 190. Use the lab manual page
as a draft and copy your final answers into the spaces shown below. Activity 8.2 is on the other side of the page and you
will need it for a future lab. Consequently, leave it in your lab manual.
A. 1. __________________
2. __________________ yr
Calculations:
3. ____________________________________________________________________________________
4. ____________________________________________________________________________________
B. Earth’s Age: ____________
Reasoning:___________________________________________________________________________________
C. 1. ______________
Explanation: ______________________________________________________________________________
2. _________________________________________________________________________________________
D. 1. _________
_________________________________________________________________________________________
2. (Hint: This is the problem with dating sedimentary rocks.)
_________________________________________________________________________________________
E. 1. _________________________________________________________________________________________
2. _________________________________________________________________________________________
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