Bacterial morphologies in carbonaceous meteorites and comet dust
  Three decades ago the first convincing evidence of microbial fossils in
carbonaceous chondrites was discovered and reported by Hans Dieter Pflug and
his collaborators. In addition to morphology, other data, notably laser mass
spectroscopy, confirmed the identification of such structures as putative
bacterial fossils. Balloon-borne cryosampling of the stratosphere enables
recovery of fragile cometary dust aggregates with their structure and
carbonaceous matter largely intact. Scanning electron microscope studies of
texture and morphology of particles in the Cardiff collection, together with
Energy Dispersive X-ray identifications, show two main types of putative
bio-fossils - firstly organic-walled hollow spheres around 10 microns across,
secondly siliceous diatom skeletons similar to those found in carbonaceous
chondrites and terrestrial sedimentary rocks and termed "acritarchs". Since
carbonaceous chondrites (particularly Type 1 chondrites) are thought to be
extinct comets the data reviewed in this article provide strong support for
theories of cometary panspermia.
