India Plate

[Anomalocaris]

24 years for Marco Polo journey, plates moving an average of an inch a year.

That’s a 2 way journey, with a 20 year sojourn in and about China in the middle. 

As it turns out, when Indian subcontinent was actually moving north towards its rendezvous with Asia, it experienced some of the fastest plate movement ever seen in geology.   Recent estimate says it was doing 11 inches a year before the docking with Asia occurred.    It is still moving north at significantly higher than 1 inch a year.   The exceptional speed of the movement of India continent into Asia is a main reason why on average the Himalayas are so tall.    If India has move slower, the material would be fed into the tectonic pile up slower, and the equilibrium between mountain building and erosion would have been reached at generally lower average altitude.

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The mountains didn't isolate them from Alexander the Great's boys.

No, it didn't. There are ways in and out, it's just that they're bottlenecks. To the west you have arid, mountainous regions of Afghanistan and Pakistan. To the east the jungles of the Indo-Chinese Peninsula. Neither are easy migration routes and anybody trying them finds that the people who migrated there first have set up a thriving civilization in the fertile lands of India and are more than capable of repelling invaders.

The first homo sapiens to reach India may well have followed either a coastal route or even a maritime route.   What is clear is Homo sapiens reaches Andoman islands in the Indian Ocean a very long time ago, possibly 60,000+ years ago.