UNIT 11
EARTH SCIENCE
CAVES ARE UNDERGROUND PASSAGES AND CAVERNS CARVED BY WATER AND LAVA. In their relatively undisturbed interiors, dripping water and volcanic activity deposit minerals that can form stalactites, stalagmites, and crystals.
Mexico’s unearthly Cave of Crystals looks like the inside of a geode. The hot, crystallized cavern lies deep underground, near a magma chamber, and some of its transparent crystals are more than 35 feet (11 m) long.
Troglobites, troglophytes, and trogloxenes are creatures who hang out in caves. While troglobites such as blind fish must spend their entire lives in caves, troglophytes are able to creep out of their subterranean dwellings. Trogloxenes such as bats pass time in caves but depend on the outside world as well. Cave ecosystems are unusual in that most caves are devoid of sunlight, making energy scarce and limiting resources.
This Earth Science unit includes labs that show you how to replicate crystal formation in caves using baking soda and how to freeze some supercool ice formations.
LAB 45
SUPERCOOL EXPERIMENT
PUSH THE LIMITS OF FREEZING IN THIS SUPERCHILL EXPERIMENT.
MATERIALS
Tap water
Large bucket or cooler filled with ice
Rock salt, sea salt, or table salt
Several 8- or 16-ounce (235 or 475 ml) bottles of purified or distilled bottled water
Bowl or plate
SAFTEY TIPS & HINTS
— Loosen the lids on the bottles and retighten gently, so they’re easy to get off.
— Water for this experiment can be chilled in the freezer.
— Once the water has frozen in a bottle, you must thaw it completely before refreezing it.
— This experiment may take several tries, so don’t get frustrated!
PROTOCOL
STEP 1: Add enough water to your bucket or cooler to come almost to the top of the ice.
STEP 2: Add about 1/4 cup (68 g) salt for every 4 gallons (15 L) of ice-water mixture. If you’re not sure how much your container holds, measure the ice and water as you add it. Remember, there are 16 cups in every gallon (3.8 L). (Fig. 1)
Fig. 1: Add ice and salt to a container.
STEP 3: Empty one or two bottles of water, label them “tap water,” and fill them with tap water. Replace the lids.
STEP 4: Set several of your bottles in the ice-water mixture so that their lids are above the ice. Make sure you include at least one tap-water bottle and one purified- or distilled-water bottle. (Fig. 2)
Fig. 2: Put bottles in the ice water to cool.
STEP 5: Chill the bottles, checking them frequently, until the water in one of the bottles freezes solid but the water in the other bottles remains liquid. It may take a few hours. (Fig. 3)
Fig. 3: Check the bottles frequently for signs of freezing.
STEP 6: Place a few clean ice cubes in a bowl or on a plate.
STEP 7: Carefully remove one of the liquid-water bottles from the ice and gently remove the lid. If it freezes, get another bottle.
STEP 8: Once you’ve found a bottle that doesn’t freeze when opened, very slowly pour the water over the ice cubes. If it’s supercooled, it will freeze instantly, piling up in a slushy column. (Fig. 4)
Fig. 4: Pour supercooled water slowly over ice.
STEP 9: If it doesn’t work, let your liquid water cool a little bit longer and try again!
STEP 10: See resources for a link to a video we took of this supercool experiment!
CREATIVE ENRICHMENT
Try this experiment with other liquids. Does it work with carbonated beverages?
LAB 46
CRYSTAL CAVES
GROW BAKING SODA STALAGMITES AND STALACTITES.
MATERIALS
Rectangular plastic container (with lid) large enough to hold 2 jars
Aluminum foil
2 jars
Hot tap water
Baking soda
Food coloring
White paper towel or napkin
Spoon or scoop
SAFTEY TIPS & HINTS
— It may take a few weeks for the crystal stalactites and stalagmites to grow. Be patient.
— This experiment won’t work as well if it’s very humid.
— If it’s going to rain, use the container lid to protect your crystal cave.
PROTOCOL
STEP 1: Create a cave by covering a plastic container with aluminum foil and turning it on its side.
STEP 2: Fill both jars with hot tap water.
STEP 3: Add several spoonfuls of baking soda to each jar until no more will dissolve and there is a layer of baking soda sitting at the bottom of the jar.
STEP 4: Add a few drops of food coloring to each jar, stir, and put the uncovered jars into the cave you made. (Fig. 1, 2)
Fig. 1: Add food coloring to the baking soda and water solution.
STEP 5: Cut two long strips of paper towel about 1/2 inch (1.5 cm) wide. Make a fold in the center of each strip.
STEP 6: Position the paper strips with their ends in the jars to form two bridges, with a low-hanging fold in the center. Be sure the ends of each bridge are submerged in liquid.
STEP 7: Wait a few minutes and check to make sure that liquid is moving from each side to the middle of the paper bridge. It will probably drip. (Fig. 3)
Fig. 3: Liquid will drip from the paper bridge between the jars.
STEP 8: Leave your cave in a sheltered area so the baking soda solution can continue to drip. Check it every day or two. If the paper dries out, spoon some liquid from each jar onto the paper to restart the dripping.
STEP 9: After several days, you should see stalactites (downward-growing crystals) and stalagmites (upward-growing crystal) forming in your cave. (Fig. 4, 5)
Fig. 4: You will see stalactites and stalagmites forming in the cave you made.
CREATIVE ENRICHMENT
Try using other solutions, such as one made from Epsom salts and water, to form crystals in your cave.
LAB 47
SOIL FILTRATION
“POLLUTE” WATER WITH FOOD COLORING AND TRY TO CLEAN IT UP WITH THE HELP OF NATURAL SOIL FILTERS.
MATERIALS
At least 2 empty 2-liter (2 qt) bottles
Jars
Rocks slightly larger than the mouth of the bottles
Sand
Topsoil
Liquid cup measure
Tap water
Science notebook
Pitcher of water tinted purple with red and blue food coloring
Grass or peat moss
Pebbles
SAFTEY TIPS & HINTS
— Don’t be frustrated if the water is very cloudy or dirty after the first step. You may have to run several rounds of water through the filters to start to see a difference, depending on the type of sand and soil you are testing.
— Do not drink the water you collect from the filter.
PROTOCOL
STEP 1: Cut the bottoms off the plastic bottles.
STEP 2: Place the bottles mouth side down into the jars.
STEP 3: Put a layer of rocks in the bottom of each bottle. (Fig. 1)
Fig. 1: Add rocks to the bottom of each bottle.
STEP 4: To one bottle, add a deep layer of sand on top of the rocks. (Fig. 2)
Fig. 2: Add sand to one of the bottles.
STEP 5: To a second bottle, add a deep layer of topsoil on top of the rocks.
STEP 6: Guess which filter will work best and then pour 1 cup (235 ml) of clear tap water over each filter to test your hypothesis. Observe and record the filtered water’s appearance in your notebook. (Fig. 3)
Fig. 3: Which filter do you think will work best?
STEP 7: Discard the water from the jars.
STEP 8: Pour 1 cup (235 ml) of purple water over each filter (the food coloring is your fake pollutant), observe the filtrate, and record the results.
STEP 9: Continue to layer materials, such as grass or peat moss and pebbles, onto the filters to see what other natural materials aid in water filtration.
STEP 10: Test your filters by pouring equal volumes of colored water over them to observe the color and clarity of the filtered water. (Fig. 4)
Fig. 4: Pour colored water over the filters.
CREATIVE ENRICHMENT
Plant chia seeds or grass on topsoil in one of the filters to test how plant roots contribute to filtration. Test the filters every week for several weeks as the roots get longer.