Now, with the help of radiocarbon analysis, the two fragments have been shown to be decades older -- which puts them among the oldest known examples in the world, according to researchers at the UK's University of Birmingham.
The testing, which is more than 95% accurate, has dated the parchment on which the text is written to between 568 and 645 AD, the researchers said.
This means it was created close to the time of the Prophet Mohammed, who is generally thought to have lived between AD 570 and 632 AD, they said.
The ancient fragment is part of the university's Mingana Collection
of Middle Eastern manuscripts, held in the Cadbury Reseach Library. They were gathered in the 1920s by Alphonse Mingana, a Chaldean priest who was born near Mosul, Iraq, but settled in England.
The two parchment leaves are believed to contain parts of Suras (chapters) 18 to 20, written with ink in an early form of Arabic script known as Hijazi.
And according to Professor David Thomas, professor of Christianity and Islam, the text is very similar to what is found in the present day Quran.
"This tends to support the view that the Quran that we now have is more or less very close indeed to the Quran as it was brought together in the early years of Islam," he said.
Written on parchment, stone, camel bones
Thomas and Nadir Dinshaw, professor of interreligious relations at the University of Birmingham, said the results of the radiocarbon analysis had been "startling" and "could well take us back to within a few years of the actual founding of Islam."
The animal from whose hide the parchment was made could have been alive in the lifetime of the Prophet Mohammed, or shortly afterward, they said in a university news release.
According to Muslim tradition, they said, the Prophet Mohammed received the revelations that form the Quran between 610 and 632 AD.
"At this time, the divine message was not compiled into the book form in which it appears today. Instead, the revelations were preserved in 'the memories of men.' Parts of it had also been written down on parchment, stone, palm leaves and the shoulder blades of camels," the researchers said.
It was only under Caliph Abu Bakr, the first leader of the Muslim community after Mohammed, that the collection of all Quranic material was ordered to be gathered in the form of a book, they said.
"The final, authoritative written form was completed and fixed under the direction of the third leader, Caliph Uthman, in about AD 650. Muslims believe that the Qur'an they read today is the same text that was standardised under Uthman and regard it as the exact record of the revelations that were delivered to Muhammad."
The researchers hailed the discovery as being of particular significance to Birmingham because the city is culturally diverse with a large Muslim population.
Susan Worrall, director of special collections at the Cadbury Research Library, described the manuscript as "a treasure that is of global significance to Muslim heritage and the study of Islam, as well as being a source of great pride to the local community."
Dr Muhammad Isa Waley, lead curator for Persian and Turkish Manuscripts at the British Library, said: "This is indeed an exciting discovery.
"We know now that these two folios, in a beautiful and surprisingly legible Hijazi hand, almost certainly date from the time of the first three Caliphs."