Re: Bronze age Argarics may have used up natural resources

On Tue, 20 Nov 2007 23:05:54 +0100, Hayabusa <peregrine@xxxxxxxxxxx>
wrote:

On Tue, 20 Nov 2007 10:16:58 +1300, Eric Stevens
<eric.stevens@xxxxxxxxx> wrote:


3. If it was a large meteor of solid, to do a favor to you: a
chondrite (rock, not iron); we would have found the impact crater long
ago. Impact craters do get noted by mapping geologists down to 5m
size. A 5-10m meteor would hit a considerable hole, say 20-100m. It
cannot have been larger because the crater would be a tourist
attraction, and there is no such thing. (The crater in the 4corner
country UT-AZ-NM-Co was 50m large.)

People only expect to find craters because for a long time craters
were the only experience people had of impacts in the past.

Oh no. An impact will cause very-high-velocity brittle deformation of
its target rock which leaves clear signs. Expect some rock to melt,
forming pseudotachylite (sudden rock melt, otherwise often found in
exhumed earthquake-prone faults), plus a variety of other features
which we have learned to see long ago. And I do not talk about giant
impacts like Nördlingen, I mean relatively small impacts.

People do not examine rock for shatter-cones etc at random. They
usually only look where they have identified a possible crater.
Without the crater there is no real evidence of an impact. It's only
relatively recently that people have started to look for
micro-spherules which leave an imprint much larger in diamter than a
mere hole in the ground.


In fact,
the vast majority of bolides never reach the ground to leave a crater.

correct.

I don't think 1, 2 or even 3 can explain the sudden widespread
ignition of an entire forest

agreed

but the thermal radiation from a
Tunguska-like event certainly could.

except that if there is evidence of widespread fires, but no evidence
of meteors, I would resort to more down-to-earth interpretations
instead of the most outrageous one.

But what evidence of meteors would you expect to find at first sight?
As I have previously stated, the most useful thing to is search for
micro-spherules.

Why do you want to use the meteor hypothesis by any means if there is
no evidence other than fire - which may be caused by a bunch of
reasons? Come up with a hand specimen of a meteor, and your position
would improve a bit (not much though). Right now you have nothing on
your hand except a wild idea which is of little practical value.

I don't _want_ to use it but I would like to think that the
possibility has been considered. It makes at least as much sense as
the idea that for their own peculiar reasons the local population
suddenly set about burning off all the vegetation in the region.

The human-caused fire interpretation makes a good deal more sense,
among other reasons because this systematic burning has been observed
in other places as well. And it must have been systematic because a
fire ove one mountainside would have grown back within a couple years,
seeded from nearby forests. The burning in Spain was followed by an
entirely different habitat which not only indicates environmental
disruption, but also relatively intense use, eg. as pasture as in the
Alps.

Unfortunately, that's not what happened.

"Not long afterwards, about 3,900 years ago, the diverse
forest ecosystem disappears, to be replaced by
monotonous and fire-prone Mediterranean scrub."

There is no mention of an intervening agricultural period and
apparently no evidence of a later new use.

It was this new use that prevented the old plant association
from growing back. Grass pastures in high mountain country will turn
back to forests if left alone even today. (Not entirely sure about
southern Spain, but sure about Calabria, which is more or less the
same thing.)

But it didn't happen, did it? A sufficiently wide spread fire could
have wiped out such an area that the green edges were too far away to
re-seed the devastated area, but what about the seeds already in the
ground? It is possible for a sufficiently intense fire to sterilise
the ground. It's a puzzle.

Hayabusa




Eric Stevens
.

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