Final answer:
Mountains like the Himalayas form slowly over millions of years due to tectonic plate collisions; this prolonged timespan exceeds the human lifespan, making it impossible for us to observe the complete formation of a mountain range.
Step-by-step explanation:
The direct answer to why we cannot directly observe the complete formation of a new mountain range within our lifetime is Option 3: The process of mountain formation is extremely slow, taking millions of years, which is longer than a human's lifetime.
Mountain ranges like the Himalayas are predominantly the result of the collision between the Indian plate and the Eurasian plate, a geological process known as orogeny. Two continental masses push against each other under immense pressure, causing the crust to buckle and fold, with some rock dragged deep below the surface and other parts rising to create high-elevation features such as the majestic Himalayas. This process began roughly 70 million years ago and continues today, with the Himalayas still rising in elevation by one to five millimeters per year. However, the sheer scale of geological time is not comprehensible within the span of a human lifetime, making it impossible to witness the entirety of a mountain range's formation from start to finish. Furthermore, the ongoing action of erosion by water and ice constantly shapes the landscape, altering the mountains' appearance over time.
Mountains such as the Rockies and the Alps have similarly formed through plate tectonics, though each range has its unique origins and mechanics. While the Rockies are the result of low-angle subduction, the Alps and Himalayas were created through continent-continent convergent boundaries. Yet, regardless of their formation processes, these ranges exhibit the slow and persistent nature of mountain building on Earth.