Final answer:
Marine fossils found at high altitudes in the Rockies are evidence of the region being submerged in an ancient sea, which was later uplifted by tectonic forces, illustrating the dynamic geological changes over time.
Step-by-step explanation:
High atop the Rockies at 8,000 feet, where fossils of marine organisms have been found, are indicative of significant geological changes over time. These fossils can be explained by the knowledge that the Earth's crust is composed of interconnected sections, or tectonic plates, which over millions of years, move and interact in various ways. The presence of marine fossils in the mountains is due to the fact that the Rocky Mountains were once submerged in an ancient sea and were then uplifted by tectonic forces. This process is known as orogeny, which involves the structural deformation of the Earth's lithosphere due to compressional forces that form mountain ranges. The fossil record, including layers of rock and the fossils within them, serves as evidence for the changes in sea level, indicating periods of submersion and emergence of different land areas over geological time.