I think, instead, that the fossil/genetic evidence points to a single source for present life forms.
From what I've read, that evidence is weak and relies primarily on a statistical guess... it is merely presumed to be more probable that the similarities in life forms are because of a single ancestor rather than parallel evolution. It could just be, however, that RNA and DNA are a natural consequence of the chemical structure of the universe that will form, again and again, given reasonably favorable conditions. Further, the extents of what constitutes favorable conditions keeps expanding rather than contracting. Until fairly recently, biologists never conceived of life thriving by deep ocean vents at near boiling temperatures without biological food or light, but it does quite well, thank you, without these niceties.
Chemosynthetic life, blood systems based on copper rather than iron (octopus), fungi, Archeabacteria (having no nucleus), and slime molds of the kingdom Protista all seem to challenge the "common descent" theories. Even within the common descent theory, there's a requirement that there was a rich world filled with rna-based life prior to dna life forms, and scholarly papers suggest that non-rna/non-dna life likley preceded those life forms including:
Robertson, MP; Joyce, GF (2012). "The origins of the RNA world". Cold Spring Harb Perspect Biol 4 (5). doi:10.1101/cshperspect.a003608. PMC 3331698. PMID 20739415.
Cech, TR (2012). "The RNA worlds in context.". Cold Spring Harb Perspect Biol 4 (7): a006742. doi:10.1101/cshperspect.a006742. PMC 3385955. PMID 21441585.