The "goldilocks" principle

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.

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  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. 

  
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  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.

  
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  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.

• 
  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.
  

Bean models of the atmosphere on the three planets (Earth, Venus and Mars)

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?
   

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?
   

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).

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).

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).

• 
  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!