One reason is that the language of Zoroastrian scriptures, the Gathas, the liturgical hymns which make up the Avesta, the Zoroastrian canon, is very similar to the oldest layer of Sanskrit, the language of the Vedas, the sacred texts of the Hindus (see here). The two languages are so close that they are ‘little more than dialects of one tongue’, and not many centuries can have separated them from their common origins.92 Since the Vedas date to between 1900 and 1200 BC, at least, the Gathas cannot be very much younger.
