Final answer:
Seismic waves from earthquakes and plate tectonics theory, supported by modern technology such as GPS, provide evidence of motion in the Earth's interior, leading to events like earthquakes and volcanic eruptions.
Step-by-step explanation:
The evidence that the interior portion of the Earth is in motion can be observed through various phenomena. Seismic waves, produced by earthquakes, are critical for understanding Earth's internal structure. These waves change velocity as they travel through different materials, reflecting and refracting in ways that indicate the Earth is not homogeneous. Through seismic imaging, akin to ultrasound, scientists can construct a model of Earth's interior, revealing liquid and solid layers. Events such as volcanic eruptions and the creation of geographical features like the Hawaiian island chain also showcase the dynamic nature of the Earth's mantle.
Plate tectonics theory further supports the idea of movement beneath Earth's surface. The Earth's crust is divided into plates that shift and move over a molten core. These movements can cause earthquakes, shift continents, and influence the formation of mountains. This is evidenced by processes such as subduction, where one plate slides beneath another, leading to seismic and volcanic activity.
Furthermore, modern technology like global positioning satellites (GPS) and very-long baseline interferometry (VLBI) allows geoscientists to measure global plate motions and provide empirical data supporting the constant movement of Earth's tectonic plates.