The Islamic conquest also brought with it the adoption of Arabic script for writing Persian and much later, Kurdish, Pashto and Balochi. All three were adapted to the writing by the addition of a few letters. This development probably occurred some time during the second half of the 8th century, when the old middle Persian script began dwindling in usage. The Arabic script remains in use in contemporary modern Persian. Tajik script was first Latinised in the 1920s under the then Soviet nationality policy. The script was however subsequently Cyrillicized in the 1930s by the Soviet government.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): When did the use of middle Persian script begin?
unanswerable