Earthworms: Air Displacement

Question: Why do earthworms come to the surface after a big rain?

Answer:

If there is a lot of rain, the rain water not only fills the burrows of earthworms but also fills the spaces between rocks and particles of soil. In other words, the rain water displaces the air between the rocks and soil particles.

Discover For Yourself

You can easily see how water can displacement air by using gravel (purchase where crafts or aquarium supplies are sold).

First of all, displace means to push something out of the way and to take its place. When water displaces air in soil or in the glass of gra

vel used for this investigation, you can see bubbles forming on the surface.

Fill a plastic see-through cup almost full with small pebbles (aquarium gravel works well).

Fill a second cup with tap water. Add 4 to 6 drops of red food coloring to the water. Stir.

Pour some of the colored water into the cup of gravel.

Watch as the colored water meanders it way between the pebbles. At first, you will see bubbles in the “puddle” of water on top of the gravel.

Continue adding the colored water until bubbling stops. Once the spaces between the gravel are filled with colored water, the bubbling stops. This is because all the air has been displaced by the colored water.

Challenge: After a heavy rain ends, see if you can find bubbles of air coming out of the ground.