The Universe (& all what is in it) has been created in “six days”.
The Creation in “six days” is a concept which the Quran, the Bible (Pentateuch), and the Avesta (Original) have in common.
Historically, the earliest written version of the Pentateuch is the translation in Greek made in Egypt at the time of Pharaoh Ptolemy II. That was in the 3rd Century B.C.E. None of the documents used for translation in Greek reached us.
The Pentateuch ‘’Genesis 1'’ verses state that the whole world has been created in six ‘’days’’. The Creationist Movement considers that the Bible is talking about 24 hours days ! Other integrist Movements think the same.
On ‘’day 4'’, the stars, the sun, the moon and earth were created. Therefore, the knowledge of scientific facts suggests that, before the 4th day of the Creation, the ‘’days’’ should be understood as ‘’periods’’.
For the Quran, I understand that the word used to describe the Creation days is “youm”, the meaning of which is closer to ‘’era’’ or ‘’period’’. In any case, they are supposed to be very long periods.
For the Avesta, it is clear that the Creation occured in six periods of time. The Original Avesta has been written around 8 to 10 centuries B.C.E.
Therefore, the Creation has been made in ‘’Six Days’’ for Zoroastrians, Judeo-Christians, and Muslims. Nowadays, people who know about the facts consider that the Lord decided to disclose it to the Zoroastrians first, then to the Jews, followed by Christans and Muslims.
It is interesting to note that the concept of Creation ‘’day’’ used by Muslims and Zoroastrians are very similar, whilst the Judeo-Christians have different understandings of the word, according the the different branches of Faith.
