For what it's worth, the base assumption of the (materialist) atheist worldview is that the natural world is a closed system (i.e. no supernatural), from which it follows that science can (at least in theory) describe all of reality. This is a very lightweight assumption, and an easy one to make, but I would point out that it is also not scientifically verifiable, as all scientific data has to be interpreted as being the result of some natural law.
For what it's worth, the base assumption of the (materialist) atheist worldview is that the natural world is a closed system (i.e. no supernatural), from which it follows that science can (at least in theory) describe all of reality. This is a very lightweight assumption, and an easy one to make, but I would point out that it is also not scientifically verifiable, as all scientific data has to be interpreted as being the result of some natural law.