From the dirt in our gardens to the liquid metal core of our planet, the earth is a place where remarkable processes happen every day without our knowledge. One of the simplest processes is the manner in which sunlight warms our planet.

QUESTION

Which gets warm faster: land or water?

MATERIALS

2 small cups

Water

Dirt

2 thermometers

PROCEDURE

• Fill one cup with water and the other with dirt.

• Place both cups in the freezer for 10 minutes.

• Remove both cups from the freezer and place a thermometer in each. Record the initial temperatures.

• Place both cups in full sunlight for a period of 15 minutes.

• After 15 minutes, record both temperatures.

WHAT'S HAPPENING

Sunlight warms the land much faster than it does water. That is why your cup of dirt ended up warmer than the cup of water. This also explains why, on a hot day, a sandy beach can get extremely warm while the water in the lake remains cool.

FOLLOW-UP

When you dig in the sand on a beach, does the sand feel warm all the way down, or is it only the top level that gets hot?2 Some animals dig into the earth to find cool places to make their nests. Can you find animals that do that?

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KIDS' LAB LESSONS

QUESTION How do icicles grow?

EXPERIMENT OVERVIEW In this experiment, you'll explore the formation of icicles by building stalactites and stalagmites — towers of rock-hard minerals usually found in caves deep in the earth. Surprisingly, the process by which they form is very similar to how icicles form. You'll be using a common drugstore product called Epsom salts and you'll get to watch the “icicles” grow right before your very eyes.

SCIENCE CONCEPT Icicles can form only under special conditions. It must be cold enough for water to freeze, but there must also be a way for ice to melt so it drips. This is why icicles are commonly found along the edge of the roof of a house. The warmth of the house can cause snow on the roof to melt and drip to the edge of the house. As the water drips off the side, some of it freezes. Later, drops run down the frozen droplets and freeze when they reach the end. In this fashion, the icicle grows drop by drop.

In caves, stalactites and stalagmites grow in the same way. The only difference is that the water that drips doesn't freeze. Instead, each drop of water leaves behind a tiny amount of calcite, which hardens on the end of the stalactite. Eventually, enough calcite builds up and hardens that a stalactite forms. Stalagmites are formed when some of the calcite falls to the ground and gradually builds up from the floor. After a long time, the stalactites that grow from the ceiling meet up with the stalagmites growing up from the floor until they join and a column is formed.

MATERIALS

Large glass that you can use for mixing

Water

Small spoon

Box of Epsom salts (available at a local drugstore)

2 small glasses

Thick string or a piece of cloth that will absorb water easily

Wax paper

PROCEDURE

• Fill the large glass with water and stir in the Epsom salts until you cannot dissolve any more (some of the salt remains and won't dissolve).

• Fill each small glass with half of the solution you have prepared and place the jars on a piece of wax paper.

• Place an end of the string in each glass and let the middle of the string hang between the glasses.

• Watch your stalactite and stalagmite grow over the next few days.

QUESTIONS FOR THE SCIENTIST

• Which of your cones is the stalactite and which is the stalagmite?____________

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• How fast did your stalactite grow (how many inches per day)?__________________

• Did the process speed up at all during your experiment?___________________

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• If you live where it's cold enough for icicles, how do you suppose they form?

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• How could you prevent icicles from forming on your house?_______________

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FOLLOW-UP

Do you think this experiment will work with other substances? Try baking soda, table salt, sugar, and so on. Considering the fact that Epsom salts is found in drugstores, can you find other uses for it?3