Ribosomal RNA as Molecular Chronometer 16S/18S rRNA gene(functionally constant, universally distributed,and moderately well conserved in sequence across broad phylogenetic distances) ATPase (membrane-bound enzyme complex that can synthesize and hydrolyze ATP) RecA(protein required for genetic recombination) Chen Feng,Shanghai Jiao Tong UniversityChen Feng, Shanghai Jiao Tong University Ribosomal RNA as Molecular Chronometer 16S/18S rRNA gene(functionally constant, universally distributed, and moderately well conserved in sequence across broad phylogenetic distances) ATPase (membrane-bound enzyme complex that can synthesize and hydrolyze ATP) RecA (protein required for genetic recombination)