Atheism is the rejection of God. If there is no God then their cannot logically be anything divine. If you deny God then you in essence deny anything supernatural. No atheist can deny God and yet accept immortality. Atheism is the admission humanity is the extent of life. Atheists therefore cannot legitimate a human soul.
Rejection implies that something exists (at least as an idea) but is being denied as fact. Atheists start by rejecting and therefore the burden of proof lies on them. No atheist can deny the idea of God. They must therefore prove that this is nothing more than an idea. The challenge of proving that a noun remain nothings more than a mental creation or figment lies on the atheists back. They question what generations of humans have assumed and believed to be true. They have not sufficiently proven anything thus far except man ability to deny and reject.