Scratching the Surface - Carving Channels

Overview

Carving Channels is a 20-30 minute activity for children ages 8–13 in which they create channel features with flowing water. Their observations of the ways in which flowing water alters the surrounding terrain will be used as clues to draw conclusions about Mars' geologic past.

What's the Point?

• Channels are surface features carved by a flowing liquid, like water.
  The types of features formed by flowing water indicate elevation of the terrain.
• The presence of channels on a planet or moon is evidence that liquid once flowed on its surface.
• Scientists are interested in knowing if water is — or was — present on other planets and moons because all life as we know it requires water. If there is or was water, life might be — or have been — present.
• Models — such as the children are using here — can be tools for understanding the natural world.
  Geologists use features on Earth to help them understand how similar features may have formed on other planets, like Mars.

Materials

For each child:

• One GSI Journal: Mars Inside and Out Or One GSI Journal Part 1: Scratching the Surface
• One pencil.

For each team of 3 to 5 children:

• About 25 pounds of clean playground sand
• 5 pounds of pesticide-free diatomaceous earth (from a home improvement or pool supply store), Cool tip: Sand and diatomaceous earth can be dried out and reused!
  
• 4 to 5 1 to 3 inch rocks
  
• 4 to 6 2-liter bottles, without lids, filled with water).
  
• Access to water to refill the bottles as needed
  
• 2 plastic wallpaper trays (from home improvement or hardware stores)
  
• 4 standard bricks
  
• 2 5 gallon or larger trash cans or buckets (rectangular shaped is best)
  
• 2 large trash bags to line the buckets or trash cans
  
• Images of channels on Mars and Earth (from the Setting the Scene activity).
  

For the facilitator:

• Background information
  
• Scissors or other tool to poke holes through thin plastic
• Shopping list

Preparation

• Prepare an area large enough to accommodate the stream tables for the number of teams participating. Each team will use two stream tables, side by side, to create and compare different types of stream features.
  
• Prepare the stream tables for Carving Channels:

Poke 3 pea-sized holes on the bottom of each wallpaper tray, about 1 inch from the end. Place the trays so that the children can easily group around them. In one of the wallpaper trays, pour one inch of sand. On top of the sand pour two inches of diatomaceous earth. Add a thin layer of sand across the surface of the diatomaceous earth. For the top layer, sprinkle just enough diatomaceous earth to cover the sand. In the other wallpaper tray, pour two to three inches of sand. Have the sand along the edges be a little higher than in the center so that water will flow down the center. Dampen the sand. As much as possible, leave the holes at the ends of both trays uncovered so the water can drain. Bury two or three rocks in each tray just beneath the surface in different locations. Position each wallpaper tray so that the end with the holes hangs over the table edge about 6 inches. Place a lined trash can or bucket under the part of the tray that extends over the edge to catch excess water as it drains from the tray. Place three bricks under the other end of the wallpaper tray with the diatomaceous earth, so it is tilted about 20 degrees. You may want to recruit help with positioning the trays on the bricks. Place one brick under the tray with the sand only, so that it is tilted about 5 degrees. Place 2 or 3 two-liter bottles beside each tray, so that each child may have one Place copies of the Mars/Earth channel images near the stream tables.

Activity

1. Introduce the children to Carving Channels. Ask the children to recall their observations of the long, narrow, wiggly features on Mars and Earth.

• What did the features look like?
  
• Did they have a name for the features? Scientists call them "channels."
  
• How were the channels different on Earth and Mars?
  
• Did the channels in both trays look the same? If not, how were the different? Some channels were narrow and winding, and others were more straight and wide.
  
• How might channels have formed on Earth?
  
• What do they think created the channels on Mars?
  

2. Divide the children into groups of 3 to 5 and have each group go to a set of trays. Ask them to observe the trays and their contents. Share with the children that these are called stream tables and they contain diatomaceous earth and sand.

• What do they notice about the way in which the trays are positioned? The trays are positioned at an angle; one tray at a steeper angle than the other.
  
• Which way does fluid, like water, flow? Water — or any fluid — flows downhill
  
• What do they predict will happen when they pour water onto the surface at the top of the tray? The water will flow downhill. It will create channel features much like the ones they observed in the images of Earth and Mars.
  
• Do they think the features in the steeply dipping tray will differ from the features in the tray tilted 5 degrees? If so, in what way(s)? Answers may vary, but may include that in the tray with a low slope, the water will travel more slowly. The size of the material may also cause a difference. Perhaps the sand will drain more.
  
• What do they think will happen when the water meets an obstacle, like a buried rock? Answers will vary, but may include that the water will stop, or go around the obstacle.
  

3. Invite one child from each team to take a water bottle, hold it at the high end of the tray and slowly pour gently and steadily into the tray with the sand.

• What features do they observe? At a slow rate and a low gradient or angle of tilt, a gently meandering stream may form. This stream will have an "s-shape" and is called a "meandering stream."
  
• Have the children observe what happens along the stream edges. Can they detect sand building out some parts of the meanders and eroding others?
  
• Do the channels they created look anything like those in the images of Mars and/or Earth? What is the same? What is different?
  
• What happens if they increase the flow rate of the water? Do the features change?
  

4. Next, invite the children to repeat the experiment with the stream table that is at a higher angle of tilt.

• What features do they observe forming? At the steep tilt and high flow rate, the flowing water will create braided streams — multiple channels — with teardrop shaped islands between the channels. The water will undercut the channel edges making slumps. At even higher rates of flow, the whole surface may flood.
  
• Do the channels they created look anything like those in the images of Mars and/or Earth? What is the same? What is different?
  
• What happened when the water met an obstacle?
  

5. After they have made their features, ask the children to carefully examine and compare the channel features in both trays. Did different features form?

• How are the features different?
  
• How do you think the angle of the landscape changes the features formed by flowing water? If the landscape tilts at a gentle angle and the flow rate is low,, the flowing water will create more organized — and fewer — channels that may form gently curving meanders. Erosion of the channel edges will be less catastrophic. At a steeper tilt — or a high flow rate- the flowing water will flood across the surface and create braided streams with teardrop shaped islands between the channels. The water will undercut the channel edges making slumps.
  
• Do these features look similar to any in the images? Yes. Both Mars and Earth have features that look like meandering channels. Mars also has some features that look like the braided channels and teardrop-shaped islands.
  

6. If you have time, smooth the surface and invite the children to experiment with squirting and pouring at various rates.

• Do different features form?
• How do the features change
• Do these features look similar to any in the images?

Conclusion

Have the children reflect on what they observed and the images from Mars and Earth. Invite them to record what they learned in their GSI Journals.

• What caused the channels in the stream tables to form? Water flowing across the surface cut into the surface and carried some of the material away.
  
• Do they observe flowing water in the images of Earth's channels? What do they conclude about how Earth's channels formed? Flowing water carved Earth's channels.
  
• Do they observe water flowing in the channels on Mars? No. What do they conclude about how those channels formed? Water carved the channels but the water is no longer there.

Facilitator Note: you may want to bring the children's attention to the fact that the water is no longer present in the channels in the stream table, but the channels are still there — the channels offer evidence that water flowed across the surface in the past. It also is possible that another fluid — rather than water — carved the channels, although there is other evidence on Mars that water is the most likely option (water exists in the ice caps, and is suspected to exist in the soil).

• What can they infer about the elevation of a terrain based on the way the channels are shaped? If the channels are gentle meanders, they can infer that the tilt of the landscape is relatively gentle. If there are braided streams and significant erosion, the gradient of the landscape is much steeper.
  
• If they observe channels on a planet, based on their model, what do they conclude about how those channels formed? Water — or another fluid! — created the channels. What does this tell them about that planet? Water was once present.
  
• What do the channels on Mars tell us about the history of Mars? Mars once had flowing water that carved the channels, but there is no evidence of water on the surface today.
  
• Why might scientists be interested in water on other planets? All life as we know it needs water. If water is — or was — present, there may be — or have been — life!