I'm by no means an expert on this subject. There are many different forms that RNA takes, and some of those forms are double-stranded, but differ from DNA in c

I'm by no means an expert on this subject. There are many different forms that RNA takes, and some of those forms are double-stranded, but differ from DNA in certain key ways. There are even "non-canonical" forms of DNA which exist whose nucleobases differ from the traditional four bases found in most DNA. Thus, you're premise that all DNA on Earth is "chemically identical" is flawed. But, if you expand the scope of your a bit, then the answer is a little more satisfying.