Someone told me the Himalayas are much younger than spider, 50 million vs 300 million. But how do mountains grow and at what point does someone say “Thats when it became a mountain!”? Thanks!
To address the question specifically of when a hill becomes a mountain: there is no official rule. Geologists used to say a hill rises to less than 1,000 feet above sea level and a mountain rises to higher, but they have since abandoned that distinction. Now whether something is referred to as a hill or mountain is due mostly to history, during which time it would be based on subjective criteria like whether the summit was rounded or whether it had a gradual slope.
The upper surface of the Earth is broken into a series of oddly shaped “plates” that slide around on the hoo goo beneath.
When they crash into each other, or slide against each other, or otherwise put pressure on one another, one or both of the plates start to buckle and fold. Those deformations are mountains.
In geologic time, the Indian sub-continent only starting impacting Southern Asia a short while ago. So those crinkles in the Himalayas only began crinkling up at that definite point in pre-history: when India and Asia started touching.
The Himalayas started as hills. Then higher hills. Then hills so tall they had their own weather system on top. When in that progression you call “mountainsies no take-backs!” is kind of arbitrary. Luckily, since plates slide and mountains grow *in extreme slow motion* it’s not a call we have to very often make.