You are presuming that the physical is all there is to existence. You fail to consider the possibility that there are portions of reality that we don't have the physical capability to perceive or the mental capability to truly understand.
There's a difference between saying "there is no evidence of X" versus "there is no evidence of X, so X is impossible"
I estimate 0.00000000%. What's your estimate?
I feel that consciousness itself is something non-physical. Whether it be a specific cocktail of neurotransmitters working in concert to give us the characteristics that we attribute to sentience, or a "core" form of existence that exists outside of our physical existence, I don't know, and I don't presume to know. I also don't presume I should be going around and acting like I can say with complete authority and accuracy "X doesn't exist in any way, shape, or form, because there is no evidence". I mean, what of the many other "scientific facts" humans have revised and subsequently rejected over a few millennia?