Dianne Newman is exploring the deep connection between bacteria and rocks -- specifically, the possibility that some varieties of ancient microorganisms gave rise over millennia to vast mineral deposits. She’s intrigued in particular by enormous banded iron formations found on every continent that contain rich evidence of the important role of bacteria.

Newman and her colleagues examine this ore in big and small chunks, and from a biochemical perspective. Buried inside lie fossils of microorganisms and their processes, and it’s by the “careful interpretation of the rock record that we make progress,” says Newman. 3.4 billion-year-old rock chunks called stromatolites contain fossil shapes that look like “microbial mats rolled up,” and filaments resembling the structures some bacteria use for photosynthesis, the process by which modern-day plants split water using sunlight to produce their food. There are also molecule-scale fossils of cyanobacteria (blue green algae), a photosynthetic microorganism, preserved in 2.5 billion year old rock. In the days before atmospheric oxygen became abundant on Earth, could primitive bacteria have used a photosynthetic process based on other elements, like iron, and yielded enormous mineral deposits over time?

To learn what microbial community might have produced stromatolites and other such rocks, Newman headed down to a salt marsh in Woods Hole, to “dig in the sand and see microbial mats with various layers of bacteria” -- cyanobacteria on the top, green and purple beneath and on the bottom, sulfate-reducing bacteria. While scientists have demonstrated that the metabolism of oxygen-producing cyanobacteria stimulates the formation of calcium carbonate minerals, it has been uncertain whether the other bacteria, which don’t produce oxygen, can do the trick of creating such minerals.