Figure 2. Closeup [field emission scanning electron microscope (FE-SEM)] of a triplet structure within the martian meteorite Nakhla with a 20 nanometer wide filament extending from the apex of a terminal sphere. The spheres appear to be partially submerged within biofilm or a later generation of "iddingsite" clay.

Figure 3. Field emission scanning electron microscope (FE-SEM) image of spheroidal features in the martian meteorite Shergotty with smectite-like clay coatings. These features and spheroidal features observed in Nakhla [Figure 2] are both similar to features in samples cultured from Columbia River Basalt [Figure 4].

Figure 4. Field emission scanning electron microscope (FE-SEM) images of spherical features in bacteria-containing samples from Columbia River Basalt. Such features were absent from sterile controls (Thomas-Keprta et al., 1998. Their morphology is similar to that of features in martian meteorites Nakhla [Figure 2] and Shergotty [Figure 3].