Geoscience Reference
In-Depth Information
tion! So the drilling needs to be done with care and in the absence of
organics. The whole adventure, however, could be a lost cause from the
beginning if organic-rich fluids have migrated through the rocks while
they were still in place underground, and this could have happened mil-
lions or even billions of years after the initial deposition. Think about
how petroleum migrates to form subsurface oil reservoirs. Another
problem is handling. Even if we can convince ourselves that we have
collected uncontaminated samples, we must be careful not to introduce
contamination as we store and process the samples, and this is harder
than it sounds. Loose hair follicles, dust, pollen, fingerprints, or a myr-
iad of nasty compounds derived from where the cores are stored; these
are all sources of contamination. This work is not for the clumsy, or for
the faint hearted.
Roger Summons from MIT in Boston worries incessantly about all
of these problems and has one of the few labs in the world that studies
biomarkers in really old rocks. His recent and very talented graduate
student Jake Waldbauer, now at the University of Chicago, worked
in rocks ranging in age from 2.46- to 2.67-billion-years-old from South
Africa. The rocks were carefully drilled, carefully collected, and care-
fully handled. The rocks themselves were free of any obvious hydro-
carbon migration or hydrocarbon generation, and after extraction, the
small amounts of biomarker recovered had the characteristics of organic
matter that was partially degraded during heating. This means that
there is no evidence of recent contamination. All in all, Jake, Roger, and
company have done about as good a job as possible.
hat they found is extremely interesting. They uncovered a number
of different types of biomarker molecules, and of interest here, they also
found a variety of sterane molecules.
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Steranes are derived from sterols,
of which cholesterol is a well-known example. Sterols concentrate in the
cell membrane, where they aid in enhancing the fluidity and flexibility
of the membrane. Indeed, sterols are universally distributed among eu-
karyotic organisms,
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including plants, animals, and fungi. Critically, as
far as we know, sterols require oxygen for their synthesis in the cell. There-
fore, where you find sterols, there was free oxygen, but not necessarily
very much. In other work, Jake showed that sterols were synthesized
by yeast (yes, yeast is a eukaryote too) with oxygen levels some 100,000
times less than one finds today in water saturated with air. Therefore, in
