Final answer:
Early geographers believed a natural landform should have considerable local relief to be classified as a mountain. This definition was based on observable topographic characteristics, but it neglected the complex geological processes that define mountain formations today, such as those related to plate tectonics.
Step-by-step explanation:
What did early geographers believe the local relief should be for a mountain to be a mountain? Early geographers typically believed that, for a natural landform to be classified as a mountain, it should possess a significant degree of local relief — that is, a distinct difference in elevation between the summit and the surrounding landscape. This notion of the 'mountain' was largely based on observable relief and basic topographic distinctions rather than on the specific geological processes or complicated interactions that formed the landform which are understood today.
Geological understanding has since evolved, and professional geographers now recognize that the formation of mountains is intricately linked to plate tectonics. From ESRI GEO Inquiry, we understand that mountain building is a complex process involving the motion of the Earth's tectonic plates. Regions that have higher elevations today may have been shaped by historical convergence between plates, and such mountain belts are subject to weathering and erosion over time. Older mountains may exhibit lower elevations today due to prolonged exposure to natural erosive forces.
The notion that solely local relief defines a mountain was limiting and neglected other key features such as geological composition, internal structure, and the ongoing dynamic forces at work, such as those described in Exercise 1.5 - Interpreting Ancient Plate Tectonic Boundaries.