Full Idea
The Gathas, the liturgical hymns that make up the 'Avesta', the Zoroastrian canon, are very similar in language to the oldest Sanskrit of Hinduism, so they are not much younger than 1200 BCE.
Gist of Idea
The Gathas (hymns) of Zoroastrianism date from about 1000 BCE
Source
Peter Watson (Ideas [2005], Ch.05)
Book Reference
Watson,Peter: 'Ideas: from fire to Freud' [Phoenix 2006], p.152
A Reaction
This implies a big expansion of religion before the well-known expansion of the sixth century BCE.