The Persian-Arabian connection (orthography, only)

Factual Questions
1

Did the Arabs base their alphabet on an earlier Persian alphabet, or did the Persians convert to an Arabic script with the introduction of Islam?

I had always assumed the latter, but I came across something where someone offered a dissenting opinion which indicated that the Arabs based theirs on an ealier Persian (post-cuneiform) script. (You can find it, too. Plug in [Persian Pahlavi alphabet] into Google, and one of the links will show up.)

I have a source that indicates that the Arabic script might have developed from some forgotten peoples known as the Nabateans , but who or what they were is not mentioned. All sources indicated that there is some debate on the matter, though.

Any thoughts from people who have knowledge on this?

(I realize that these two languages have nothing in common philologically, other than loan words. This query is just about the writing.)

2

“arabic script origins”

Arabic script is derived from the Aramaic Nabataean alphabet.

The evolution of distinct Arabic characters, which were later used to develop the Arabic scripts, were derived from the Nabataean script and date back to the third century.

Arabic language…probably developed in the 4th century CE as a direct descendant of the Nabatean alphabet.

The North Arabic script, which was influenced by the Nabatian script, was established in north-eastern Arabia and flourished in the 5th century among the Arabian tribes who inhabited Hirah and Anbar…Nabataen Inscription providing proof of origins of Arabic script. from 6th century, begins with Allah Ghafran- 'May God forgive…

The Nabateans were the ones who built Petra, the “Stone City”.
http://www.kinghussein.gov.jo/his_nabateans.html
http://www.jewishgates.org/history/jewhis/nabat.stm
http://www.petramoon.com/nabatean.html

Cool pix.
http://www.onemanandhismac.co.uk/Jordan/Petra1.html

“Persian pahlavi script origin(s)” doesn’t turn up much.

My vote is for Arabic descending from the Nabateans, and then the Persians adding Arabic to their Sassanid Persian Pahlavi with the rise of Islam.

3

Persians definitely converted their script to Arabic after they took up Islam/were invaded by Arabs. They wound up having to add an extra four letters, though – Arabic only has 28; the Farsi speakers added a p (as in pea), a ch (as in chicken), a g (as in golf), and a zh (as in measure).

The funny thing (at least to me) is that while the Persians had to add those letters, there were a stack of other letters that they had no use for. Three separate Arabic letters are pronounced as ‘s’ in Persian, two are ‘t’, two are ‘h’, and no fewer than four are ‘z’.

I still don’t understand why, if you’re going to invade a place and force your alphabet on them, you don’t just make them learn the language that goes with it as well. Although I’ve read that 40 % of Farsi vocabulary is Arabic loanwords, so maybe they tried…