I'll let Sojourner answer from his knowledge base, but I think part of the answer to that, is that when you read the text, it says following the statement that God created the heavens and the earth in verse 1, describing how in the following verses beginning with verse 2:
Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters.
What you see here is a formless, unshaped, unmolded raw materials of something already there which God then took and fashioned in the following verses by separating light and dark, water and land, etc. It was then upon this prepared creation, that God populated it with various creatures, cultimaning in the creation of humans.
Now, outside the Bible, historically speaking, it was not until the 10th century A.D., that an ex-nihlo creation was proposed. Prior to that time, everyone believed in creation from pre-existing matter. From the Wiki article on just that:
Saadia Gaon introduced ex nihilo creation into the readings of the Jewish bible in the 10th century CE in his work
Book of Beliefs and Opinions where he imagines a God far more awesome and omnipotent than that of the rabbis, the traditional Jewish teachers who had so far dominated Judaism, whose God created the world from pre-existing matter.
[29] Today Jews, like Christians, tend to believe in creation
ex nihilo, although some Jewish scholars recognise that Genesis 1:1 recognises the pre-existence of matter to which God gives form.
[30]
Creatio ex nihilo - Wikipedia