Name: ______________________________
THE ATMOSPHERE AND LIVING THINGS
INTRODUCTION
The Gaia hypothesis proposes that Earth is one huge organism. The parts of Earth consist
of living things and environmental factors, existing in a balanced state. If one part changes, the
other parts will also change to maintain this balance, as longs as the changes are relatively small.
However, large changes in one part of Earth can greatly alter the biosphere. The perception of
Earth as one giant living being is highly controversial, but the idea that it maintains a balance
between living and nonliving parts is widely accepted. This interaction between living and
nonliving things can be observed in Earth’s changing atmosphere. Life on this planet has adapted
to a changing atmosphere. These life forms have, in turn, altered the atmosphere. Read page 78
in your textbook for more information about the Gaia hypothesis.
In this investigation, you will plot the percentages of various gases present in Earth’s
atmosphere. You will then construct a graph depicting changes in the atmosphere through time,
and identify major geological events on the same graph. You will then interpret the graph,
relating the events to the atmospheric changes.
WARM UP
A useful way to show change through time is to plot data on a graph. Scientists use graphs to
visualize trends they cannot readily observe from raw data acquired in their research. A cumulative graph
shows data of several different types. A cumulative graph is especially useful when showing the
composition of something, or the amounts of different parts that make up the whole.
Suppose a scientist is studying how the bird population on a small island has changed over the
last 150 years. To visualize the data, the scientist might use a cumulative graph (Figure 1.1). Notice that
each portion of the bird population is built upon the previously graphed data. The blackbird percentages
are graphed first, by plotting the actual percentages in the population. The bluebird percentages are built
upon the blackbird. For the year 1900, for example, the percentage of bluebirds in the population was
50% minus 30%, or 20%. For the same year the percentage of redbirds in the population was 85% minus
50%, or 35%, and the remainder of the population (100% minus 85%, or 15%) was composed of other
species of birds. For any given year, the sum of the percentages of all categories is always 100%.
Percent of total bird population
Figure 1.1 Cumulative graph of bird population on island
100%
Other
80%
Redbird
60%
40%
Bluebird
Blackbird
20%
0%
1850
1900
1950
Year
2000
Page 2
PROCEDURE
1. Figure 1.2 illustrates the composition of Earth’s atmosphere at different times in the planet’s
history. Plot the percentages of the gases on the graph provided. Your graph should be a
cumulative graph; use the graph from Figure 1.1 on the front of this sheet as a guide. First
observe that the amount of carbon dioxide in the atmosphere 4.5 billion years ago was 80
percent. Plot that number in the appropriate space on the graph.
2. The next gas in the chart is nitrogen. Using a different color, plot a point 10 percentage
points higher on the graph, at 80 + 10, or 90% of the total atmosphere. Proceed with the other
gases in this manner. Use a different color to plot the points for each graph.
3. After all the points are plotted, connect the points plotted for each gas, producing a curve for
each. This curve represents gradual change over time.
4. Colors the areas representing different gases. For example, the area beneath the line drawn
for carbon dioxide represents the proportion of carbon dioxide in the atmosphere. Shade this
space with the color you used when plotting the points for carbon dioxide. Label all gases.
5. Figure 1.3 lists some important events in Earth’s history. Write the events underneath your
graph next to the times they occurred.
Figure 1.2 Composition of Earth’s atmosphere from Earth’s formation until present
Gas
Carbon dioxide
Nitrogen
Hydrogen
Oxygen
Other gases
4.5
80%
10
5
0
5
4.0
20%
35
3
0
42
3.5
10%
55
1
0
34
Billions of years before present
3.0
2.5
2.0
1.5
1.0
8%
5%
3%
1% 0.07%
65
72
75
76
77
0.5
0
0
0
0
0
0
1
5
10
26
23
21
18
13
Figure 1.3 Major geological events in Earth’s history
Geological Event
Billions of Years Ago
Origin of Earth
4.5
Formation of oldest known rock
3.9
First evidence of organic matter in rocks
3.7
Photosynthesis evolves in plants
3.0
Limestone deposits become common
1.8
Many fossils of marine invertebrates
0.55
Earliest land plants
0.44
Earliest land animals
0.40
Dinosaurs dominant
0.17
0.5
0.04%
78
0
15
7
Present
0.025%
78
0
21
1
Page 3
OBSERVATIONS
Evolution of Earth’s atmosphere
100
% of total atmosphere
80
60
40
20
0
4.5
4.0
3.5
3.0
2.5
2.0
Billions of years
before present
1.5
1.0
0.5
Present
Page 4
DATA ANALYSIS
Answer the following in complete sentences.
1. What gas has made up the largest proportion of Earth’s atmosphere for most of Earth’s history?
What about this particular gas explains why its proportion in Earth’s atmosphere has increased?
2. How does the appearance of photosynthetic plants relate to the increase in atmospheric
oxygen and the decrease in carbon dioxide?
3. Limestone is composed of calcium carbonate (CaCO3). Protists use free calcium ions (Ca+) from
the sea to form calcium carbonate shells. Which gas appeared in the atmosphere about the time
when limestone deposits became common? Why might this be so?
4. If the trends seen in the graph continue, how will Earth’s atmosphere change in the next 500
million years?
5. The changes in the atmospheric levels of oxygen gas and carbon dioxide gas were due to life
processes. In the case of carbon dioxide, recent human activities have also influenced its
atmospheric proportion. What was the cause of the elimination of hydrogen gas in Earth’s
atmosphere? Research this question and summarize your findings below.