Re: New Scientist: Toba explosion supports Oppenheimer

On Jul 15, 6:33 am, Brian Pears <bpe...@xxxxxxxxxxxxx> wrote:
CWatters <colin.watt...@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

You can test the accuracy of Strontium isotope analysis in modern
humans. You can ask people where they grew up and then check to see if
that matches the strontium data and to what degree it matches. Sure
it's not a proof but if the geology is right you can be reasonable sure.

The use of strontium isotope analysis to pinpoint where
early humans grew up can not be absolutely relied on because
we are assuming a lot and can never back those assumptions.

That isn't necessarily the case when other complimentary techniques
like trace rare earth and heavy metal signatures can be used to
identify (fairly accurately) the soil type at the locality where an
individual grew up or lived most recently. Scientists worry a lot
about the assumptions that are required in any form of dating or
geographical matching. And also about whether or not the fossil has
been able to ion exchange significantly with its environment. Choice
of specimen is severly limited by this latter consideration.

It is only really likely to be a problem in the band of land close to
the sea. And people living there would likely leave a lot of old shell
debris that would warn researchers. The techniques are improving all
the time in sensitivity and ease of use - it is already possible to do
time resolved analysis of isotope ratios and elements in some fossil
specimens (although not so far as I know applied to human remains
yet).

Modern humans are a bit of a disaster for any kind of food locality
traceability. Look at the number of things in your local supermarket
that have travelled half way round the world. But in most of history
and pre history unless very rich you would be unlikley to eat anything
fresh that had travelled a substantial distance (more than a couple of
days ride?).

For example, the results of strontium isotope analysis are
seriously skewed in cases where fish formed a large part of
the childhood diet? The same would presumably be true if
they'd eaten a lot of migratory birds. Did those particular
early humans eat a lot of fish in their childhood! As with
so many things about that period, we just don't know!

The fish would show up as a maritime diet. But I don't think any of
the researchers these days rely entirely on a just single stable
isotope method like Sr for their determinations. Only migratory birds
with a predominantly fish diet would skew the Sr data significantly -
land based birds would be OK.

And in ancient times there were no huge inland municipal landfill tips
full of seagulls that never go to sea.

The thing that is well established is that if you are a carnivore,
omnivore or herbivore it can be reliably determined by Sr isotope
measurements when combined with certain other elemental ratios. The
closest publically accessible paper describing some of the research
online is by Sponheimer & Lee-Thorp at Colorado:

http://melampus.colorado.edu/class/pdfs/SponheimerandLeeThorp2006GCA.pdf

The same rare earth trace element signature trick also works
exceedingly well on gold from mines and fine wines - and has been used
effectively in criminal prosecutions of fraudsters. I think the first
successful use in a criminal case was in the mid 1990's.

Consequently all we can ever do is to construct hypotheses
which explain the evidence to date. As more evidence emerges
which is compatible with an hypothesis it can be used to
refine that hypothesis. But we can never prove the hypothesis
because there's always the possibility that incompatible
evidence will emerge - and any incompatible evidence means
that the hypothesis is wrong and we need a new hypothesis
which is compatible with the new evidence as well as the old.

You are what you eat is at largely true. Cheap supermarket chicken
tastes slightly of oily fish waste to me, and real corn fed ones are
not a horrible lifeless ashen grey colour whereas fake corn fed ones
are too yellow. The same "you are what you eat" rule is what causes
the demise of raptors when pollutants are concentrated up the food
chain (and the fact that they were last in line when God was
installing livers).

Regards,
Martin Brown

.

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