Bacterial morphologies in carbonaceous meteorites and cometdust

摘要

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. SEM studies of texture and morphology of particles in the Cardiff collection, together with EDX identifications, show two main types of putative bio-fossils – firstly organic-walled hollow spheres around 101.1M 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.