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The "goldilocks" principle


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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

VENUS

EARTH

MARS

Surface Pressure Relative to Earth










Major Greenhouse Gases










Estimated Temperature if No Greenhouse Gases (°C)










Actual Temperature (°C)










Temperature Change Due to Greenhouse Gases













Atmospheric Concentrations of Greenhouse Gases (%)

VENUS

EARTH

MARS

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?



  1. 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.





  1. 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.




Temperature and Pressure Comparison

Atmospheric Concentrations of Greenhouse Gases (%) on Venus

Surface Pressure Relative to Earth

90

Carbon Dioxide (CO2)


96.5

Major Greenhouse Gases

CO2

Nitrogen (N2)


3.5

Estimated Temperature if no

Greenhouse Gases (°C)



-46

Oxygen (O2)


Trace

Actual Temperature (°C)

477

Argon (Ar)


0.007

Temperature Change Due to GHG

+523

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. 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

Atmospheric Concentrations of Greenhouse Gases (%) of Mars

Surface Pressure Relative to Earth

0.007

Carbon Dioxide (CO2)


95

Major Greenhouse Gases

CO2

Nitrogen (N2)


2.7

Estimated Temperature if No Greenhouse Gases (°C)

-57

Oxygen (O2)


0.13

Actual Temperature (°C)

-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

Atmospheric Concentrations of Greenhouse Gases (%) on Earth

Surface Pressure Relative to earth

1

Carbon Dioxide (CO2)


0.03

Major Greenhouse Gases

H2O, CO2

Nitrogen (N2)


78

Estimated Temperature if No Greenhouse Gases (°C)

-18

Oxygen (O2)


21

Actual Temperature (°C)

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

Main sources

Water Vapor (H20)

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

Venus

Earth

Mars

CO2

96

1

95

N2

3

76

3

O2




21

1

CH4




1




Ar

1

1

2

Total Number of beans

100

100

100

Total in Atmosphere

9000

100


0.6


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