The palimpsest codex shows two layers of script. The parchment upon which the lower codex is written has been radiocarbon dated with 99% accuracy to before 671 AD, with a 95.5% probability of being older than 661 AD and 75% probability from before 646 AD. This was an ancient way of recycling.) Alternatively, the standardization of the Qur'anic text by 'Uthmān may have led to the non-standard lower text becoming obsolete, and thereby erased. When enough of a manuscript's writing wore off-ink does not bond to parchment like it does to paper-all of the writing was washed off to make the expensive parchment usable for a new text. (This was a common practice in ancient times. A number of reasons may have led to erasure of the lower text: some pages of the codex may have been destroyed or worn out, thereby requiring the production of a new codex, for which the already available parchment was used. The lower text of the manuscript was erased and written over, but due to the presence of metals in the ink, the lower text has resurfaced, and now appears in a light brown color. Carl Ernst, an Islamic studies scholar, states that the manuscripts 'do not appear to have any startling or major changes but belong to the class of minor textual variations that have been known for centuries.' Variants occur much more frequently in the Sana'a codex, which contains 'by a rough estimate perhaps twenty-five times as many '. Such variants are similar to the ones reported for the Qur'an codices of Companions such as Ibn Mas'ud and Ubayy b. For example, in sura 2, verse 87, the lower text has wa-qaffaynā 'alā āthārihi whereas the standard text has wa-qaffaynā min ba'dihi. While the upper text is almost identical with the modern Qur'ans in use (with the exception of spelling variants), the lower text contains significant diversions from the standard text. Of special importance is a palimpsest with two layers of text, both of which are Qur'anic. The preserved fragments comprise Qur'anic and non-Qur'anic material. Al-Akwa' sought international assistance in examining and preserving the fragments, and in 1979 managed to interest a visiting German scholar, who in turn persuaded the West German government to organize and fund a restoration project. Qadhi Isma'il al-Akwa', then the president of the Yemeni Antiquities Authority, realized the potential importance of the find. Not realizing their significance, the workers gathered up the documents, packed them away into some twenty potato sacks, and left them on the staircase of one of the mosque's minarets. In 1972, construction workers renovating a wall in the attic of the Great Mosque of Sana'a in Yemen came across large quantities of old manuscripts and parchments, many of which were deteriorated. Radiocarbon analysis has dated the parchment containing the lower text to before 671 AD with a 99% accuracy. The upper text conforms to the standard 'Uthmanic Qur'an, whereas the lower text contains many variants to the standard text. The manuscript is written on parchment, and comprises two layers of text (see palimpsest).

It was found, along with many other Qur'anic and non-Qur'anic fragments, in Yemen in 1972 during restoration of the Great Mosque of Sana'a. The Sana'a palimpsest is one of the oldest Qur'anic manuscripts in existence.

Sana a manuscripts