3.1.6 Goldilocks Activity
THE “GOLDILOCKS” PRINCIPLE
Materials:
Atmosphere models of beans in baggies
Resource Cards 1-5
Task Card
Recording Sheets (one per student)
Background
On Earth, two molecules, nitrogen (N2) and oxygen (O2), make up almost 99% of the
volume of clean, dry air. Most of the remaining 1% is accounted for by the inert gaseous
element, argon (Ar). Argon and the tiny percentage of remaining gases are referred to as trace
gases. Certain trace atmospheric gases help to heat up our planet because they appear
transparent to incoming visible (shortwave) light but act as a barrier to outgoing infrared (long
wave) radiation. These special trace gases are often referred to as "greenhouse gases" because
a scientist in the early 19th century suggested that they function much like the glass plates
found on a greenhouse used for growing plants.
The earth's atmosphere is composed of gases (for example, CO2 and CH4) of just the
right types and in just the right amounts to warm the earth to temperatures suitable for life.
The effect of the atmosphere to trap heat is the true "greenhouse effect."
We can evaluate the effect of greenhouse gases by comparing Earth with its nearest
planetary neighbors, Venus and Mars. These planets either have too much greenhouse effect or
too little to be able to sustain life as we know it. The differences between the three planets
have been termed the "Goldilocks Principle" (Venus is too hot, Mars is too cold, but Earth is
just right).
Mars and Venus have essentially the same types and percentages of gases in their
atmosphere. The atmospheres of both of them are primarily CO2 and they are very different
from the Earth. However, they have very different atmospheric densities.
Venus has an extremely dense atmosphere, so this density combined with the concentration
of CO2 (96.5% of the atmosphere) is responsible for a "runaway" greenhouse effect and
a very high surface temperature. Mars has almost no atmosphere; therefore the amount of CO2 (95% of the atmosphere)
although similar to that of Venus is not sufficient to supply a warming effect and the
surface temperatures of Mars are very low.
Mars is much further away from the Sun than is Venus.
Adapted from The Goldilocks Principle: A Model of Atmospheric Gases
http://www.ucar.edu/learn/1_1_2_1t.htm
TASK CARD: GOLDILOCKS PRINCIPLE
Without greenhouse gases, what would happen to the Earth? We will look at Earth’s two
closest planets to see what is happening in their atmospheres.
Greenhouse gases are invisible molecules in the atmosphere. They let sunlight energy into the
atmosphere, but they are able to trap it so it can’t get back out. In the earth, there are several
important greenhouse gases. Table 3 lists the main gases and their sources.
Our neighboring planets either have too much greenhouse gases or not enough. Mars and
Venus have very similar types of GHGs in their atmospheres, but they are different in the
density of gas.
 Venus has an extremely dense atmosphere, so this density combined with the concentration
of CO2 (96.5% of the atmosphere) is responsible for a "runaway" greenhouse effect and a
very high surface temperature.  Mars has almost no atmosphere; therefore the amount of CO2 (95% of the atmosphere)
although similar to that of Venus is not sufficient to supply a warming effect and the surface
temperatures of Mars are very low.
 Mars is much further away from the Sun than is Venus.
Materials:
Bean models of the atmosphere on the three planets (Earth, Venus and Mars)
Resource Cards 1-5
As a group, discuss the following questions.
1. Do the bags all look the same? Why or why not?
2. Using the tables on the three planet resource sheets, complete the table on your
worksheet.
3. What would the temperature on each of the three planets be like without greenhouse
gases?
4. Why is it so much colder on Mars than on Venus, even though they have similar
amounts of carbon dioxide?
5. Name at least two ways that the atmospheres of Venus and Mars are similar to each
other, and one way that both differ from Earth's.
6. Why do we call this the “Goldilocks” principle?
RECORDING SHEET: Why is Earth the GOLDILOCKS planet?
Temperature and Pressure
Comparison
Surface Pressure Relative to Earth
VENUS
EARTH
MARS
VENUS
EARTH
MARS
Major Greenhouse Gases
Estimated Temperature if No
Greenhouse Gases (°C)
Actual Temperature (°C)
Temperature Change Due to
Greenhouse Gases
Atmospheric Concentrations of
Greenhouse Gases (%)
Carbon Dioxide (CO2)
Nitrogen (N2)
Oxygen (O2)
Argon (Ar)
Methane (CH4)
1. Why is it so much colder on Mars than on Venus, even though they have similar
amounts of carbon dioxide?
2. Name at least two ways that the atmospheres of Venus and Mars are similar to each
other, and one way that both differ from Earth's.
3. Why do we call this the “Goldilocks” principle?
RESOURCE CARD 1: GOLDILOCKS
VENUS
Too much greenhouse effect:
The atmosphere of Venus, like Mars, is
nearly all carbon dioxide. But Venus has
about 300 times as much carbon dioxide
in its atmosphere as Earth and Mars do,
producing a runaway greenhouse effect
and a surface temperature hot enough
to melt lead.
The atmosphere on Venus is much
denser than the ones on Mars or Earth.
If we represented the density with
beans, Venus would have 9000 beans
compared to 100 on Earth.
Surface Pressure Relative to Earth
90
Atmospheric Concentrations of Greenhouse
Gases (%) on Venus
Carbon Dioxide (CO2)
96.5
Major Greenhouse Gases
CO2
Nitrogen (N2)
3.5
Estimated Temperature if no
Greenhouse Gases (°C)
Actual Temperature (°C)
-46
Oxygen (O2)
Trace
477
Argon (Ar)
0.007
Temperature Change Due to GHG
+523
Methane (CH4)
Temperature and Pressure Comparison
0
The relative distance from the Sun has some influence on planetary temperature, but the
greenhouse gases and atmospheric density have more of an impact on temperature. Venus has
an extremely dense atmosphere (with a surface pressure 90 times that relative to Earth's
atmosphere). Conversely, Mars has an extremely thin atmosphere (with a surface pressure less
than 1/100th of that relative to Earth's atmosphere).
RESOURCE CARD 2: GOLDILOCKS
MARS
Not enough greenhouse effect: The
planet Mars has a very thin
atmosphere, nearly all carbon
dioxide.
Because of the low atmospheric
pressure, and with little to no
methane or water vapor to reinforce
the weak greenhouse effect, Mars
has a largely frozen surface that
shows no evidence of life.
Temperature and Pressure Comparison
Surface Pressure Relative to Earth
0.007
Atmospheric Concentrations of Greenhouse
Gases (%) of Mars
Carbon Dioxide (CO2)
95
Major Greenhouse Gases
CO2
Nitrogen (N2)
2.7
Estimated Temperature if No
Greenhouse Gases (°C)
Actual Temperature (°C)
-57
Oxygen (O2)
0.13
-47
Argon (Ar)
1.6
Temperature Change Due to GHG
+10
Methane (CH4)
0
The relative distance from the Sun has some influence on planetary temperature, but the
greenhouse gases and atmospheric density have more of an impact on temperature. Mars has
an extremely thin atmosphere (with a surface pressure less than 1/100th of that relative to
Earth's atmosphere).
RESOURCE CARD 3: GOLDILOCKS
EARTH
The right amount of greenhouse
effect?
The Earth has small amounts of
carbon dioxide and other
greenhouse gases, but working
together they create a balanced
system that helps to support life.
US!
This model does not take into
account the importance of water
vapor as a greenhouse gas.
Water vapor both helps warm the
planet, when it is in the form of a
gas, and cool the planet, when it
is in a reflecting cloud.
Temperature and Pressure Comparison
Surface Pressure Relative to earth
Major Greenhouse Gases
1
H2O,
CO2
Atmospheric Concentrations of Greenhouse
Gases (%) on Earth
Carbon Dioxide (CO2)
0.03
Nitrogen (N2)
78
Estimated Temperature if No
Greenhouse Gases (°C)
Actual Temperature (°C)
-18
Oxygen (O2)
21
15
Argon (Ar)
0.9
Temperature Change Due to
Greenhouse Gases
+33
Methane (CH4)
0.002
The relative distance from the Sun has some influence on planetary temperature, but the
greenhouse gases and atmospheric density have more of an impact on temperature. Venus has
an extremely dense atmosphere (with a surface pressure 90 times that relative to Earth's).
Conversely, Mars has an extremely thin atmosphere (with a surface pressure less than 1/100th
of that relative to Earth's).
RESOURCE CARD 4: GOLDILOCKS
Major Greenhouse Gases and their Sources
Greenhouse Gas
Water Vapor (H20)
Main sources
Water in the air as clouds or vapor.
Carbon Dioxide (CO2)
Burning fossil fuels, deforestation, land use changes,
respiration, volcanic eruption
Methane (CH4)
Decomposition of wastes in landfills, agriculture
(especially rice production), cattle digestion, manure
management
Nitrous Oxide (NO2)
Soil cultivation practices (how we grow plants) use of
fertilizers, burning fossil fuels, biomass burning.
Chloroflorocarbons
(CFCs)
Human made compound originally made to use as a
coolant in refrigerators and air conditioners. Now
regulated in production and atmosphere release
because of international agreements to limit use.
RESOURCE CARD 5: GOLDILOCKS
Beans in a Bag Models
Scientists use models to help describe a complex system. Sometimes you need to simplify
the system for the model. These bags contain very different colored beans, but they all have
the same total number of beans. That's not the way it is on the real planets. Venus has an
atmosphere 90 times thicker than Earth's and Mars has an atmosphere more than 100 times
thinner! If you made a bag with 100 beans to represent Earth's atmosphere, then to show the
correct density of the atmosphere, your Venus bag would have 9000 beans, and your Mars bag
would have less than 1 bean!
Bean Bags for Atmosphere Concentration Models
To make the bags of atmosphere, you can use this table to help you. This is to demonstrate the
relative proportions of each gas in the total atmosphere. Each bag or atmosphere should have
100 beans in it. If you were to simulate the actual amount of each gas, you would multiply the
proportion by the relative amount to Earth (for Venus, X 90; for Mars X 0.6).
Gas
Concentration
CO2
N2
O2
CH4
Ar
Total Number
of beans
Total in
Atmosphere
Venus
Earth
Mars
96
3
95
3
1
1
100
1
76
21
1
1
100
2
100
9000
100
0.6