Robert Folk's first career won him a medal. He established the naming system for limestones, as well as doing important groundwork in describing sediments and classifying sedimentary rocks. Then Folk retired in 1988 (he's an emeritus professor at the University of Texas Austin) and started playing with an electron microscope.
"Nannobacteria" Discovered
Soon he found extremely small objects in various rocks. They look like fossilized bacteria, except that they're a fraction of a micron in size—as small as 30 nanometers. This is far smaller than biologists believe bacteria could be, and indeed biologists have found few signs of living bacteria this tiny.
Folk named his objects "nannobacteria" and began to publish papers about them. Note the spelling: biologists talk about nanobacteria, in reference to nanometers, whereas Folk has something else — nannofossils — in mind. "Nanno-" is an older prefix long used by geologists (but maybe we should retire it).
Folk's nannobacteria occur in many different rocks. He has found them in meteorites, too, and he even believes they are in the Martian meteorite ALH84001, the one in which signs of ancient life have been postulated. Microbiologists strongly rejected his idea from the beginning. But in March 2003 a geologist and a biologist created particles just like Folk's by letting food rot.
"Nannoballs" Probed
The research team consisted of geologist Jürgen Schieber, a specialist in shale at Indiana University, and biologist Howard Arnott, a specialist in biomineralization at the University of Texas at Arlington. While they were experimenting with fossilizing bacteria in the lab, Schieber and Arnott noticed "abundant spheroidal features in the nannobacteria size range, the likely precursors of so-called nannobacteria in sedimentary rocks."
Rather than use Folk's term, which explicitly refers to living things, they picked the more neutral word "nannoballs" for these objects. (Unfortunately, physicists studying extremely small particles use the term "nanoballs." We really should retire that "nanno" prefix.)
Schieber and Arnott zeroed in on their nannoballs with a series of experiments reproducing the conditions that lead to fossils. They put pieces of fresh organic matter (bean, beef and squid) between layers of clay and left them to decay. As bacteria moved in and broke the tissues down, the pieces showed abundant tiny spheroids under the electron microscope. Undecayed samples, prepared and examined the same way, had no nannoballs.
Next they repeated the experiment using not bacteria, but a mixture of purified enzymes that bacteria use to break down proteins. The enzymes worked the same way, though somewhat slower, and yielded nannoballs. Clearly nannoballs are created as decay bacteria attack organic matter—they are like crumbs on the dinner table. Schieber and Arnott speculated that as the enzymes cut apart large proteins, the pieces curl into balls as an intermediate step before they break into soluble molecules that bacteria eat.
The Germ-Crumb Model
Given that objects this small can be rapidly fossilized, Schieber and Arnott's conclusion is clear: "Most if not all alleged nannobacterial structures in sedimentary rocks are probably by-products of bacterial degradation of organic matter and not evidence for minute life forms called nannobacteria." Their study was in the August 2003 issue of Geology.
If this conclusion holds up under further study, then Robert Folk will see his cherished theory discarded. Indeed, while Folk is still highly regarded, his theory has almost no support among geologists. Medical researchers are predisposed to see bacteria, though, and a handful of microscopic studies pursued this line of research. Lately (see the December 2009 Scientific American) they have found that nannoballs in living matter are an intriguing byproduct of the body's calcium-control mechanism as crystallizing minerals interact with proteins.
But Folk's discovery is still important, perhaps more important than before. Nannoballs appear not to be living things, but they may still be strong signs of life. And that includes life in the Martian meteorite.
PS: This is an example of why terminology matters. If Folk hadn't been so fixed on his notion that the objects are organisms, he could have given them a more neutral name. That's one reason geology has so many strange words.
