Avesta
“Zoroastrian literature thus spans over three thousand years. The oldest texts are those contained in the Avesta . There is no identifiably historical information in the Avestan texts, but the language and contents are similar to those of the Rigvedic hymns, the oldest of which can be dated to approximately 1500– 1000 BCE. It is therefore likely that the oldest part of the Avesta , the Old Avesta (including the Gāthās), had reached its final form by about 1000 BCE and the Young Avesta before the Achaemenid period, perhaps during the Median period (ca. 700– 550 BCE). The indigenous history of the Avesta is described in the ninth century Pahlavi texts, among them the Dēnkard, according to which the Avesta was divided into twenty-one nasks (literally “bundles” ?)...”1
“...corpus of sacred texts of the Zoroastrians”2
“Old Avestan...mid to late second millennium BCE (oral transmission) [include:]
Gathas
Yasna Haptanghaiti
[Old Avestan] Prayers
...Young Avestan...early to mid-first millennium BCE (oral transmission) [include:]
[Young Avestan] parts of the Yasna
Videvdad (Vendidad )
Visperad
Yashts
Khordeh Avesta
Hadokht Nask
Herbadestan
Nerangestan
...sixth/seventh century CE, Avestan corpus written down”3
1 Prods O. Skjærvø, The Spirit of Zoroastrianism, The Sacred Literature Series (New Haven [Conn.]: Yale University Press, 2011), 2.
2 Jenny Rose, Zoroastrianism: An Introduction, Introductions to Religion; I.B. Tauris Introductions to Religion. (London: I.B. Tauris, 2011), 251.