Background
The Earth has changed dramatically and repeatedly over a history that spans nearly 5 billion years. Such immense spans of time are difficult for most of us to comprehend. They fall outside our range of human experience. We normally deal with much shorter time intervals, like the time of our next class or the number of days until the next test, or even the number of years until graduation!
It is important for students of geology to expand their sense of time. Extremely slow geologic processes, considered only in terms of human experience, have little meaning. To appreciate the magnitude of geologic time and the history of our incredible planet, you will be creating a timeline of important geologic events scaled to a size more tangible and familiar.
Procedure
Part 1: Follow instructions below to create a geologic timeline on a strip of adding machine paper.
You will be making a timeline of Earth’s history on a long strip of adding machine paper. The timeline should be done to scale. A scaled representation requires that 10 cm on your timeline represent the same amount of time anywhere along the timeline and each amount of time, say 5 million years, be represented by the same distance throughout the timeline. To do this you will:
a) Measure out a strip of adding machine tape 4.6 meters long using a tape measure. .

b) Select one end of the tape to represent the Present. Beginning at that end, mark off each billion years (1 billion, 2 billion, etc.)

c) Starting with the oldest event (Event #1), mark off all of the important events in Earth’s history shown in the “Some Important Events in Earth’s History” Figure on the next page. In each case you should write the date and event directly on the timeline.

d) Add in these divisions of geologic time to your timeline: Precambrian Era, beginning of the Paleozoic Era, beginning of the Mesozoic Era, and beginning of the Cenozoic Era. Use the geologic timescale included with this lab to determine dates.

Part 2: Scaling Geologic Time
Always remember to show math work, if appropriate and always, always, always include units with your final answer.
Conversions
1 billion years = 1000 million years
1 meter = 100 centimeters
1 centimeter = 10 millimeters

1. How many millions are there in a billion?
2. In lab, you will make a timeline 4.6 meters long to represent the 4.6 billion years of Earth’s history:

a) How long would 1 billion years be on the timeline?

b) How many years would 100 cm represent?

c) How many years would 10 cm represent?

d) How many years would 1 cm represent?
e) How many years would 1 mm represent?

Some Important Events in Earth’s History
Event # Date in years before present Event
1 4.6 billion Earth forms
2 4.4 billion Oldest mineral grain found
3 4.1 billion Oldest piece of rock ever found
4 3.9 billion Oldest evidence of a continent
5 3.8 billion First evidence of life
6 3.5 billion First fossils (algae and bacteria)
7 1.8 billion Free oxygen in atmosphere
8 1.1 billion First fossil of a complex organism (a worm)
9 540 million First abundant complex life in rock record
10 460 million First fish
11 440 million First land plants
12 410 million First land animals
13 250 million Largest mass extinction occurs
14 247 million First dinosaurs
15 240 million First mammals
16 220 million Breakup of super-continent Pangaea begins
17 145 million First flowering plants
18 65 million Dinosaurs and other animals go extinct
19 30 million Mammals/flowering plants become abundant
20 5 million Beginning of Cascade Volcanic Arc
21 1.8 million First primate in genus Homo
22 40,000 Homo sapiens reach Europe
23 13,000 Humans first inhabit North America
24 10,000 End of last Ice Age
25 8,000 Founding of Jericho, the first known city
26 2,000 Roman domination of the world
27 500 European rediscovery of the Americas
Part 3: Percent Calculations. Use your timeline to answer the following questions.

1. What percentage of geologic time is represented by the following subdivisions?
   Precambrian _ %
   Phanerozoic Eon _ %
   Paleozoic Era _ %
   Mesozoic Era _ %
   Cenozoic Era __ %
   Show one of your calculations here.
2. What percentage of geologic time have the following organisms been on Earth?
   Life _ %
   Fishes _ %
   Flowering plants _ %
   Humans _ %
   Show one of your calculations here.
3. Suggest a reason for how the boundary between the Precambrian and Phanerozoic Eon was decided.

Sample Solution

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