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branching features associated with some of Bill's original fossils, which
were not recognized by Bill in his descriptions. The style of the branch-
ing observed by Martin seemed to lack obvious microbial counterparts.
Martin also carefully surveyed the rocks for other possible biogenic
features and found that there was plenty of organic carbon in the rock,
but it ranged in size and shape from blobs to more organized structures
resembling fossils. In the end, Martin concluded, quite in contrast to
Bill, that the features originally interpreted as “cyanobacteria” were not
cyanobacteria at all, and indeed, they were not even fossils. In Martin's
view, these pseudofossils could best be explained by inorganic pro-
cesses. He explained that the organic matter, mobile in these rocks as
they were heated to high temperatures deep in Earth, concentrated
around quartz grains and gave rise to a variety of shapes and even to
fossil-like accumulations in some cases. Martin also noted that the geol-
ogy of the deposits may be more complex than originally appreciated.
hile Bill viewed these deposits as accumulating on something like a
beach, or at the mouth of a river, more recent reconstructions suggest
that they were formed deep within Earth. A setting deep in Earth would
not be an expected place for cyanobacteria, given their need for light,
unless the particular rock pieces housing the fossils were somehow trans-
ported from a more favorable environment.
Like a game of high-stakes poker, Martin's concerns compelled a re-
sponse from Bill, wherein he used even more advanced imaging tech-
niques (Raman spectroscopy) to ascertain that indeed the walls of the
“fossils” are kerogen (a kind of resistant organic matter) and that the
kerogen seemed to form, at least in some cases, distinct compartments
resembling cells (see
ig. 6.5)
. Martin countered again and argued that
these “cells” are merely organic carbon coating quartz grains. Bill again
countered that was not the case. We have not likely heard the end of
this discussion, but the original idea that these forms represent “prob-
able” cyanobacteria has been taken off the table, even by Bill. Therefore,
if the argument centers on whether these forms represent early evidence
for life on Earth, the evidence might be there, but other evidence is
both older and less controversial. Indeed, there is good evidence for life
in the carbon isotopes preserved in the older rocks of Isua, as explored
above. Furthermore, carbon isotopes in rocks of similar age to the Apex
Chert seem to provide evidence for life as well.
14
And as we explored in
