ADDING IT ALL UP
Introduction:
Time can be expressed using a time line. In this activity, you will make a time line that will
go all the way back to the time when scientists think that the earth was formed,
approximately 4.6 billion years ago.
Certain isotopes have suitable half-lives to be used as geological clocks to determine the
age of rocks that contain these elements. Complex laboratory procedures can be used to
determine the amount of the parent and daughter elements present, and relate this
information and the constant half-life to geologic time. Radiometric dating using various
sets of isotopes, such as Uranium-Lead, Potassium-Argon, and others, has lead
scientists to estimate the age of the earth to be over 4 billion years.
In addition to dating rocks, scientists can use Carbon 14 to date organic materials such
as wood, charcoal, or bone (not mineralized). All living things contain the element carbon
and have a constant proportion of radioactive Carbon 14 to the more common Carbon-12
isotope. The date of organic remains can be estimated by comparing the ratio of these
two isotopes. In addition to being limited to organic remains, this method is applicable
only in dating events within the past 100,000 years since the half-life of Carbon-14 is only
5,730 years.
The dates given in this activity were determined by using various radiometric dating
methods. All of the dates have been rounded off to even numbers since the time span is
so great and these dates indicate major changes on the earth.
Objectives:
After completing this activity, you will be able to:
1. identify the major geologic eras representing the earth’s history;
2. use the visual representation of the time line to compare the lengths of each era;
and
3. identify major events (mountain building, appearance of major groups of plants
and/or animals, changing oceans, etc.) which are associated with each time period
of earth’s history.
Grading: Periods and eras labeled _________ 2 pts
Major geologic events
__________ 3 pts
Timeline to scale
__________ 2 pts
Representative plants and animals
__________ 4 pts
Mix of fossil and illustrations
__________ 3 pts
eras color coded
__________ 1 pts
5 examples from Evolving Planet
__________ 5 pts
Materials: metric ruler, scissors, glue or tape, colored pencils or markers, adding
machine tape, Geologic Time Scale (Figure 2-H), Prehistoric Plant and Animal Picture
Sheet (Figures 2-I), and resource books of geologic events.
Procedure:
1. Using 1mm to represent 1,000,000 years, cut a length of adding machine tape to
represent all 4,600,000,000 years of earth’s history. How long will the adding machine
tape be?
2. Fold your adding machine tape into sixteen equal parts by folding the length in half
and repeating the process until you have sixteen equal parts. Then, refold the tape
along the same fold lines so that the tape opens up accordion style.
3. Use a three- hole punch along the length of the tape while it is still folded. This will
allow you to place the tape in a three ring binder for easy transport or storage.
4. Draw a horizontal line along the entire length of the tape about one centimeter from
the top of the tape as shown in Figure 2-G. Then divide this small section in half by
drawing another horizontal line parallel to the first one about 0.5 centimeter from the
top of the tape.
(Figure 2-G)
Sample Time Line
5. To use the table calculate the difference between when the tertiary began and when
the quarternary began. This will give you the length of time of the tertiary period.
6. Starting from the present time at one end of the tape and using figure 2-G as a guide,
measure and mark the length of the Cenozoic, Mesozoic, Paleozoic, and
Precambrian Eras by drawing a vertical line on the adding machine tape to separate
each era (remember that 1mm equals 1,000,000 years).
7. Use the small sections along the top of the tape within the first 0.5 centimeter of the
width to label each era. Color code the Cenozoic, Mesozoic, and Paleozoic Eras by
shading the top sections lightly(2pts). Be sure to choose unique colors for each era.
(do not color the Precambrian because it takes too long!)
8. Use the sheet I gave you to calculate how long each period was. Then convert this
into mm. Remember 1 million years (my) equals 1 mm. Measure and mark off period
divisions within eras by drawing vertical lines across the top to create small sections
beneath the color coded eras. Label each period and then color code each section
with light shading. Use a unique color so that no two periods have the same color.
Make sure you have plants and animals for each period. (2pts)
9. To get representative flora and fauna (plants and animals) you have 2 options. You
can use the image sheet I gave you and cut and paste those on your timeline or you
can to the Field Museums “Evolving Planet” website to get information and images for
your timeline. You can go to other websites, but this site will give you both fossil and
representative images. (4pts) Figure 2-I shows pictures of major plants that flourished
during various times in the Earth’s past. Cut them out and attach them within the
correct time periods. You need to have 5 of these on your time line. (5 pts) Also, you
need to have a mixture of artistic representations and fossils pictures. (3 pts)
10. Use your earth science textbook and other reference books to research major
geological and climatic events that happened in the past. Label these events at the
appropriate position on your time line. A few have been listed on Figure 2-H to get
you started. I gave you a sheet with these listed. (3pts)
11. Answer the Interpretation Questions. (5 pts)
Interpretation Questions:
1. About how long did each era last?
2. Compare the length of the Cenozoic Era with the Precambrian.
3. How many years ago did the first organisms appear on earth?
4. What changes mark the end of the Mesozoic Era and the beginning of the Cenozoic
Era?
5. What changes mark the end of the Paleozoic Era and the beginning of the Mesozoic
Era?
6. Which era and period are we living in?
7. Geologic time units (eras, periods, epochs) are not regular in length like other units of
time such as decades, centuries, and millienia. What are the divisions of geologic
time based upon. (Hint: look at your answer to questions 4-5?
8. Do you think that human beings or dinosaurs have been the most successful life form
to live on earth to date? Explain and justify your answer.
1mm = 1 million years
10mm =1cm
Time line breakdown of eras
ERA
PERIOD
Quarternary
CENOZOIC
Tertiary
Cretaceous
MESOZOIC
Jurassic
Triassic
Permian
Pennsylvanian
Mississipian
PALEOZOIC
Devonian
Silurian
Ordovician
Cambrian
Proterozoic
PRECAMBRIAN
Archean
TIME IN MILLION YEARS LENGTH
1.6 my
65-1.6 = 63.4 my
1.6 mm
63 mm