Those who have utmost confidence in science often note that the unexplained doesn't mean unexplainable and challenge those who claim God is the ultimate explanation with the question, "Who created God?"
Granted, science has hypotheses that explain subatomic particles, DNA, supernovas, etc. But in my view, science can explain only that which belongs in the time-space realm, and as long as the unexplained is time-space related, science has the potential of explaining it in due course.
But science doesn't have that potential when dealing with the unexplainable, which I associate with lack of time and space (LTS), a realm that is beyond time-space. For example, while the smallest (or largest) number may be explainable by science, zero (or infinity) remains unexplainable. Likewise, while science can tell us that a person is thinking, it cannot tell us what the person is thinking. Similarly, while science can build a sophisticated robot, it cannot instill survival instinct, free will or reproductive desire in the robot. Science is also unable to explain why life cannot be generated from purely inanimate objects.
Regarding "Who created God?" the key is to realize that, basically, creation involves mere rearrangement of already existing time-space matters. Creation is a process, and as such, inherently entails an expenditure of time and has a clear significance only in the time-space realm. But the question "Who created God?" attempts to extend a mundane time-space-bound notion of creation beyond its limits to address God, an LTS-related, time-space-independent concept. As such, the question is inherently inconsistent, and thus, moot.