A group of students conducted an activity about Earth's interior. They followed these steps:
Make a mixture of sand, toothpicks, and pennies in a bowl.
Fill a large clear container with water.
Pour the mixture into the container with water.
Record your observations.
One of the students recorded her observations as shown below.

Observations: The pennies sank to the bottom of the container the fastest. The sand covered the pennies, and the toothpicks floated on top of the water.

What did this activity most likely show about Earth's interior?