The brilliant 18th Century chemist, Antoine Lavoisier
(1771-1794), is quoted as saying, 'I consider nature a vast chemical
laboratory in which all kinds of composition and decompositions are
formed.' It is often folly to paraphrase the accepted genius of Lavoisier,
but the work that we undertake at particle accelerators (such as Diamond and SSRL) has enabled us to extend this
chemical insight to life through deep time. It might now be fair to say, 'We
consider nature, both past and present, a vast chemical laboratory in which all kinds of composition and
decompositions are formed, which are occasionally preserved as fossils'.
The
study of decaying bodies has provided useful data on the various stages of
decomposition that might give clues to the time and type of burial
environment. It is remarkable that as soon as a heart stops beating, oxygen that was so critical to life process ceased to circulate and
internal anoxic conditions rapidly develop. In the absence of oxygen cells
began their auto-destruct sequence, this is called autolysis. Here the cells
self-destruct courtesy of enzymatic digestion. While the tissues of an organism are still relatively soft, prior to rigor mortis setting in,
blow and flesh flies all take there chance to colonise a corpse with their
eggs and soon to be voracious larvae (who we know and love as maggots).
Tissue chemistry of living animals provides a useful elemental recipe to diagnose and then identify in fossils. |
If
there are no scavengers around to chomp through our dead body, fly maggots will
soon compensate for this. Within 24 hours flesh can often be moving again, not in a
zombie-like state, but with the writhing bodies of maggots, feasting on rotting
flesh. Maybe I should have suggested at the beginning of this blog that you not
read this close to meal times? Whilst the maggots are munching from
within a carcass, soil microbes start the process of multiplying on the new food source beginning to ooze from the various orifices of a body into the
underlying soil. Microbial communities that were once symbiotic with an animal
in life, living in the respiratory system, gut and intestine, also begin to
multiply and consume their host. This is the ultimate in organo-recycling systems. The organic acids and gases (including methane
and hydrogen sulphide) generated as by-products of the microbes metabolism soon
begin to change carcass colour and start to bloat the body, accompanied by the
distinctive rotting smell...as my anatomist friend Dr. Dino Frey might say, 'It has all gone soft and soupy'.....we all have days like that!
Decaying modern carcasses can provide evidence as to how fossils might preserve delicate organic molecules. |
The
combined efforts of insects, microbes and possibly scavengers would make short
work of our deceased beastie. Most of the body fluids would soon be 'released' into the surrounding soil, causing an initial dye-off of vegetation (due to nitrogen
toxicity), leaving a deathly halo around the body. The maggots would pupate soon after having eaten their fill. All is quiet on the recycling front to the causal observer, but not to the geochemist, as things have only just started to get interesting. Depending on the soil porosity and permeability
beneath a body, the sediments would also be directly affected by the gentle ebb of decay
juices from the body...yum! As the soil microbes get a free dinner, they also begin to process the vast influx of nutrients from
the carcass. Metabolic by-products of the microbes also begin to alter pore-water
chemistry, giving rise to the precipitation of early mineral cements to bind
the soil particles. The stink of decay marks the availability of reactive chemistry. The once living animal is now entering the immortal realm
of fossilisation. The bodies of all living organisms are a wonderful store for elements that once released (or partly released) from their biological bonds
can complex to form different species of mineral. Here is the
paradox. Release too many of the organic building blocks to the inorganic
processes and you reduce the amount of organism that remains to
be fossilised. This is a bizarre 'two-horse' race between decay and
fossilisation...one that we rely on being a close draw.... especially if we are to search any fossil remains for a whiff of original biochemistry that might still lurk within the mineralogical straight-jacket. This is precisely why we need to use some of the most sensitive imaging technology in the world to tease-out this astoundingly dilute organic signal, through working at synchrotrons light sources such as Diamond and SSRL.
Splendid fun!
Memory trigger - was this decaying cow image in one of your lecture slides in Manchester? Trying to recall from 5 years ago!
ReplyDeleteYes....this is a particularly fun dead cow, that I regularly disinter for lectures. If you were an undergrad at Manchester, you might well have seen this beastie...along with a pile of subsequent lovely images of decay.
ReplyDelete