The title of the article indicates that the rock might be from mercury, so there is no one claiming to have proved it's origin. However, there is the possibility of being pretty certain. (the main question being how did it get from Mercury to Earth?)
Spectroscopy lets us know what Mercury is made of and comparing this rock to what we know of mercury will allow scientists to determine the likelihood of a rock coming from that planet.
As an atheist, I have to chime in here and say that is a pretty broad statement to back up. Furthermore, it is not true.
I personally know many protestants who don't accept a literal interpretation of the bible, including ministers and youth ministers.
Your statement lumps Southern Baptists together with UCC and it is simply inaccurate. Additionally, my own denomination, Unitarian Universalism his strong roots in Protestantism, but is based on a non-literal interpretation of the bible and today members may not even read the bible.
Fundamentally, there may be no basis for anything.