An item in a list of news reports over at Primordial Blog caught my eye this evening. It is a report in CBC News about a paper in the most recent issue of the journal Geology describing what is believed to be ichnofossils in 3.5 billion years pillow basalts from Australia.
Ichnofossils, or trace fossils are not the remains of organisms themselves but tracks left by organisms that become preserved. In this case the traces are tunnels in the volcanic rock presumably left by microorganisms as they degraded the rock to mobilize nutrients contained within. The images on the left are from a 1998 report (Fisk, M. R., Giovannoni, S. J. & Thorseth, I. H. (1998) Alteration of Oceanic Volcanic Glass: Textural Evidence of Microbial Activity. Science, 281, 978-980.) describing these tunnels from oceanic basalts. The scale bars are 50 and 10 microns long in the top and bottom panels respectively.
There is some controversy over whether these tunnels are due to the activity of microbes or are the result of some poorly understood form of abiotic chemical weathering. These images are not easy to get as the rock has to be cut into think slices with a diamond saw and then polished to allow light through. The sections that were used to take the images shown here were 30 microns thick.