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RE: mass extinctions and technology

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Mark Harvey
> You have got to start somewhere.  To my knowledge, the organic
> environmental geochemistry of  extinction boundary sediments has
> never been
> examined.

Not so: organic (carbon isotope and other) geochemisty has been examined for
at least the K/T, and to a lesser degree some of the other events.

> You are forgetting the dimension of time.  We may be abundant and
> widespread, but for how long?   One of the explanations given for SETI
> (search for extraterrestrial intelligence) NOT receiving any alien
> broadcasts is that civilizations capable of  radio technology
> don't last long.

While this would be true for the radio record (Fermi's paradox does indeed
neglect the time component) this would not necessarily hold for the
geological record.  We would not have to recover ALL the places humans
occupied (or dropped their trash), just a couple, in order to recognize they
we were here.

> >We have engaged in largescale transformation of the surface of the earth:
> >the foundations of shopping malls, airports, strip mines, etc. are some
> >rather large and distinctive trace fossils!!  (Particularly the
> latter, as
> >they actually enter the rock rather than merely unconsolidated
> sediment or
> >soil).
> Shopping malls and airports are relics of the last 100 years.
> This gives
> them a very short window of opportunity for preservation.  How
> much of the
> pyramids will remain in even another 10,000 years?

Quite a bit of the basal stones, and a lot of the quarries.  (In fact, the
primary evidence that would remain would, as in archaeology, be primarily
the unintended stuff: trash dumps, strip mines, houses and cars buried by
floods of the Mississippi or Hawaiian lava flows, etc.)

Also, what they lack in history shopping malls and the like make up for in
number, thereby increasing their chance of recoverability.

> >We have been responsible for mass extinctions, but also for the
> large scale
> >homogenization of the terrestrial (and to a lesser degree
> aquatic) biota of
> >the Earth; useful and pest species are conciously (or unconciously)
> >transported by us across the planet.
> This homogenization could be obscured by an associated mass extinction /
> climate change = sea level instability.

However, we don't have to resort to the theoretical here. We a) have a
terrestrial fossil record and b) see no evidence at present there IS
taxonomic homogenization save for the Pangaean Late Triassic (and even here
there is regionalization).  Both terrestrial and marine paleobiogeography
are topics of some interest, and the expected results of a presence of a PHC
have yet to manifest themselves.

> >All these factors will make our presence exceedingly preservable.
> I think limited visible (> 1mm) evidence of our civilization may survive,
> but a combination of factors might render the evidence hidden,
> unrecognizable, or simply unrecognized.  ie. scarcity, burial, erosion,
> metamorphosis or confusion with contemporary trash.

I would argue against most of these.
Scarcity. This can always be used as an ad hoc defense for PHCs.  However,
given our current sample and given some theoretical basis (of an organism
capable of transforming some substantial part of the biomass to its own use)
we would expect that a PHC would easily be capable of population increases
in the exponential mode, as we have done.

Burial, erosion, metamorphism. If we are talking about PHCs evolving in the
later Phanerozoic (say the mid-Paleozoic onward) then the only remains that
would be lost to metamorphism would be through deep burial or those on (at
the time) continental margins, which have since been turned into mountain
ranges by collisions or lost through subductions.  Nevertheless, we still
have substantial records of parts of the Earth throughtout this interval.

Confusion with contemporary trash. This would be unlikely when you crack
open a Permian shale and find the trash therein! Remember that other
materials with similar preservability to garbage (i.e., animal parts,
leaves, twigs, pollen & spores, etc.) are routinely recovered from ancient
sedimentary rocks.  If they weren't, there would be no science of

> >The only
> >way that I envision our presence not being recoverable in the 10s-100s of
> >millions of years time scale would be if, for some reason, all Holocene
> >sediments and surfaces were somehow removed from sampling.  This
> seems very
> >unlikely.
> It would certainly by recoverable, but you would have to be
> looking for the
> right tracers in the right environment.

I would argue not, particularly if the traces are physical rather than
chemical.  That is, we can easily recognize a worm burrow or Paleocastor
(ancient beaver) burrow when we come across them; an ancient strip or tunnel
mine should be much more recognizable given its scale, and eminently more

> Good point, but maybe such disruption has been metamorphosed.  Also, I do
> not know the estimated depletion of  earths late Paleozoic coal
> deposits.  If  we have only scratched the surface of these deposits, then
> this would reduce the chance of the same deposit being mined twice.

Actually, there are pretty good estimates for their distribution, abundance,
and resource size (as you can imagine, there are many vested interests in
getting this information!).  True, some of these resources were obviously
lost during erosion of the Appalachians and other regions.  Nevertheless,
there do not appear to be big erosional surfaces that one would expect if a
coal-based technology utilized substantial portions of this limited

> I totally agree with you .  It takes an impact scenario these days to get
> the public interested in mass extinction (see the first five minutes of
> "Armageddon" where Bruce Willis clubs golf balls at the Greenpeace
> protesters from his oil platform).  Try to tell someone that the earth is
> warming by .5 celcius every 10 years and they will yawn and turn up the
> sport on the television.


> No-one was invoking an impact hypothesis until the boundary sediment's
> inorganic geochemistry was checked for by Walter Alvarez.

For the K/T, no, although it had been suggested long ago for the Late
Devonian extinction.  Furthermore, the Alvarez team wasn't even
investigating the K/T extinction event, despite popular claims to the
contrary.  They were instead simply trying to find out how much time was
represented by the boundary clay, using what they hoped would be a
time-averaged stable preservable tracer.  Unfortunately, the assumption of
time-averaging was a bit skewed in this instance... :-)

> I think an alien landing is far less likely to leave globally ubiquitous
> geochemical footprint.  Having said that, NASA will probably get
> around to
> checking for these compounds on Mars before anyone bothers to check
> earth.  I think the real reason we are slow to check  these old
> sediments (
> from the perspective of organic environmental geochemistry) is that:
> 1.  The technology has only been around to do so for 20 years


> 2.  We think we are pretty special (see the dark ages when we literally
> thought the univers revolved around us)

See rather the points I suggested previously: i.e., without additional
supporting evidence one might not run the costly analyses.  That being said,
there has been a LOT of examinations of organic and inorganic material at
the K/T boundary, and some (but less so) at other boundaries.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796