Inside Mars - Differentiation Demonstration

Overview

In this 10 minute demonstration or 30 minute activity, children, ages 8 to 13, observe a mode of planetary differentiation, the organization of planetary interiors into layers of different densities, to illustrate why Mars and other planets have cores, mantles, and outer crusts.

What's the Point?

• The interiors of the inner, rocky planets are organized into layers of different densities. Each has a dense core, a mantle of intermediate density, and a crust that is comprised of the least dense materials.
• Planetary differentiation is the process by which planetary interiors organize into layers of different densities.
• The planets originally were a mixture of materials; a major period of planetary differentiation occurred early in their history.

Materials

For each child:

• One GSI Journal: Mars Inside and Out Or One GSI Journal Part 2: Inside Mars
• One pencil

For the group, or for each group of 3 to 4 children:

• 1 clear plastic 2-liter soda or water bottle with a cap and with the label removed
• 3 1/2 cups (a little over 3 pounds) small aquarium gravel, preferably metallic colored
• 3 ounces of plastic (pony) beads
• Close to 6 1/4 cups (50 oz.) of corn syrup
• 4 ounces of water
• A funnel
• Measuring cups
• Three clear plastic cups

For the Facilitator:

• Background information
• Shopping list

Preparation

• Prepare a Differentiation Demonstration bottle. If the group is large, consider making more than one Differentiation Demonstration bottle before you start, so that the children can examine what happens in smaller groups.

Using the funnel, pour the gravel, corn syrup, and beads into the 2-liter bottle. Seal the bottle tightly! Put a few beads in one of the clear cups. Put some Karo syrup in another cup. Put some gravel in the third cup. Alternatively, have groups of children create their own differentiation bottles. While messy, the children enjoy this activity.

Activity

1. Invite the children to gather in a central location to share their ideas about the interiors of Earth and Mars.

• Is Mars — or Earth — composed of only one, or several different, layers? Mars and the Earth each are composed of several layers.
• What are the names of those layers? Crust, mantle, and core.
• How might these layers be different?
• Why might Mars and Earth have layers?

2. Share with the children how Mars and Earth and the other inner rocky planets formed. A little over four and a half billion years ago, dust and gas and tiny particles, mostly made of iron and rock, were in a disk surrounding our early Sun in the region where the inner, rocky planets of Mercury, Venus, Earth, and Mars eventually would be. This material began to clump together, or accrete. With time, the small clumps grew larger and larger. The largest ones swept up the smaller clumps (through gravitational attraction), eventually becoming the planets of the inner solar system. These planets did not have any layers — all the materials that made them were mixed up together.

3. Show the materials in the cups to the children, and share that you have all of these ingredients mixed together in a big bottle.

• What do the children think will happen when you mix them together?
• Will they stay mixed?
• Will some sink to the bottom? Which? Why?
• Will some float? Which? Why?

4. Show the children the Differentiation Demonstration bottle. Shake the bottle vigorously — be careful as it is heavy and takes vigorous shaking, and then set it on the table.

• What happens? The materials separate. The gravel sinks, the beads float.
  
• Were the children's predictions correct?

Conclusion

Invite the children to record their observations in their GSI Journals..

• What might the model represent when the materials have settled? How might this relate to what we may see inside Mars? The layers in the bottle represent the layers in Mars.
• What might this model represent in the story of how Mars and Earth developed? How all of the materials that made up Mars or the Earth first started — all mixed together.
• Why does the gravel sink and the beads float? The materials in the water have different densities. The "heavier" gravel sinks because it is more dense than the water, and the "lighter" straws float because they are less dense than the water. Sometimes some of the materials get "caught" in the wrong layers. This also happens inside planets.
  
  

How does this model help us understand what might have happened inside Mars and Earth to create layers? The materials separated. The most dense materials (probably mostly iron and nickel) sank to the center of the planets to make their cores. The least dense materials make up the crusts, and the material in between makes up the mantles.

Facilitator Note: The process of differentiation is much more complex than this model shows. While the cores of the planets probably differentiated early and quickly in their history, the process of differentiation of the core, mantle, and crust continue today. Volcanism is part of this process! Volcanism forms new crust, and further differentiates the mantle.