Final answer:
The students' activity likely demonstrates Earth's differentiation process by showing the separation of materials based on density, similar to how Earth's layers have formed.
Step-by-step explanation:
The activity conducted by the students likely demonstrates the concept of differentiation, a process that has shaped the interior structure of Earth. Differentiation is the sorting of materials by density, with denser materials sinking and less dense materials rising. This would explain why in the student's experiment the pennies, representing denser materials like metals, sank to the bottom; the sand, which could represent silicate minerals, settled above the pennies; and the toothpicks, representing less dense materials, floated on top of the water. This physical change is analogous to how Earth's layers have formed over time, with the densest materials forming the core, and the less dense materials forming the mantle and crust.
Scientists use various tools like seismic waves, drilling technologies, and core samples to determine the depth and composition of Earth's layers. The experiment of pushing a clear plastic straw through layered Play-Doh and pulling it out to observe the 'sediment' layers mimics the way geologists retrieve core samples to study the Earth's stratification.