Schopf claimed to have discovered bacteria fossils in these
rocks. He published his results in a highly cited Science paper
back in 1993 (Schopf, 1993). The title of the paper
"Microfossils of the Early Archean Apex chert: new evidence of
the antiquity of life" establishes his claim. It's worth quoting
the abstract of the paper because it shows the confidence Schopf
exuded. Not only did he claim that the 3.5 billion year old Apex
chert contained bacterial fossils but, even more astonishingly,
he identified eleven different species and clearly stated that
they resembled cyanobacteria. Eleven taxa (including eight
heretofore undescribed species) of cellularly preserved
filamentous microbes, among the oldest fossils known, have been
discovered in a bedded chert unit of the Early Archean Apex
Basalt of northwestern Western Australia. This prokaryotic
assemblage establishes that trichomic cyanobacterium-like
microorganisms were extant and morphologically diverse at least
as early as approximately 3465 million year