How old is the civilization in India?

Sanskrit is a language related to ancient Greek, Latin and to modern English. The speakers of these languages are thus called Into-Europeans.
But in India/Pakistan more ancient civilizations existed than those built by Indo-Europeans.

The Harappan civilization disappeared suddenly.

In Mohenjo-Daro, one of their cities, traces of radiation was found in human skeletons. These humans died suddenly in the streets and not in their homes. Nuke war in India thousands of years ago?

Sudden changes are the norm on earth as well. Floods, volcanic eruptions, asteroid impacts, ice ages, massive animal extinctions… Not gradualism but catastrophism explains the earth history much better.

Nonetheless, the disappearance of ancient Indian civilization does not match with such events.