PLEASE NOTE:


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Date sent: Mon, 30 Jun 1997 15:47:59 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: Abrupt climate changes from ~30,000 to 15,000 BP
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

from: Bob Kobres <bkobres@uga.cc.uga.edu>
-------------------------------------------

From: http://www.acs.ohio-state.edu/units/research/archive/guliya.htm

RESEARCHERS DATE CHINESE ICE CORE TO 500,000 YEARS

COLUMBUS, Ohio -- A team of scientists has reconstructed a detailed
climate record for the last 130,000 years from a thousand-foot-long ice
core they drilled into a glacier on the Tibetan Plateau in 1992.
Analyses suggest that the record in the core actually may go back more
than 500,000 years.

The ice core draws a vivid picture of a climate that changed frequently
and dramatically in that region throughout the last glacial sequence --
an interval that reached back 110,000 years through the last glacial
period and into the warm stage, the Eemian, that preceded it. Their
report was carried in this week's issue of the journal Science.

Ellen Mosley-Thompson, professor of geography at Ohio State University,
said that the extreme age of the ice at the bottom of the core isn't
the most important discovery coming from the analysis. "A record of
this length from the sub-tropics is truly unprecedented,"
Mosley-Thompson said. "It's good that we've got very old ice at the
bottom but the age of the ice is almost secondary to the amount of
detail the core provides."

With support from the National Science Foundation, the National
Geographic Society, Ohio State and the Chinese National Science
Foundation, an international expedition retrieved the core five years
ago from the Guliya Ice Cap, a 77-square-mile glacier sitting 22,014
feet high in the Kunlun Shan Mountains of western China. Although
Guliya is in the sub-tropics the ice is very cold, making it a valuable
reservoir of ancient climate records.

The team, headed by Lonnie Thompson, professor of geological sciences
at Ohio State, used mechanical and then thermal drills to remove a
1,012-foot (308.6-meters) core from the ice cap. The core, which
reached through the ice to bedrock, was split and divided between
Chinese and American researchers.

Ohio State researchers cut their half of the core into 34,800
individual samples that were then tested for oxygen isotope ratios,
dust, pollen, and nitrate, chloride and sulfate ions. Each of these
give clues to the climate in the area when the ice was originally
formed. After five years of analysis, the researchers discovered the
following:

-- The detailed record dates back 130,000 years making it the oldest
recovered from a tropical or sub-tropical ice cap. Ice at the bottom of
the core may be even older. Before now, a core Thompson drilled from
the Dunde ice cap in China was the oldest with an age of 40,000 years.

-- The record also shows that during the last glacial sequence, there
were three or four periods called interstadials when the temperature
warmed to more like those today. These warm events occurred when
methane, a greenhouse gas, was more abundant in the Earth's atmosphere.

These warmer interstadials, along with carbon dioxide and methane
increases, were first identified in cores taken from polar ice caps but
they appeared as only modest changes. The changes in the Guliya core
are quite substantial.

-- And within parts of the core representing 15,000 to 33,000 years
ago, researchers found evidence of about 100 "abrupt climate changes"
as inferred from the oxygen isotope record. During this time, the
oscillations occurred about every two centuries.

To gauge temperature changes, the researchers measure the ratio of
oxygen-18 to oxygen-16 in the ice. A reduction in the proportion of
oxygen 18 molecules generally indicates a drop in atmospheric
temperature as well.

"The isotope ratio changes seemed to indicate a temperature shift of up
to 30 degrees C," explained Keith Henderson, a graduate fellow at the
Byrd Polar Research Center. "But we know that would be ludicrous. We
need to come up with a much better explanation for these data."

Thompson and his colleagues have spent 20 years seeking out stable ice
sheets from the tropics and subtropics, and retrieving the climate
records they hold. Polar ice caps such as those in Greenland and the
Antarctic are so large that they can control their own weather. But the
much smaller non-polar ice caps respond more directly to changes in
their climate, making them excellent research tools for studying past
climate variations of shorter duration.

"The tropics and subtropics cover half of the Earth's surface and house
more than 75 percent of the human population," Thompson said. Changes
in this region can have profound impacts.

For years, researchers have assumed that the climate in the tropics and
sub-tropics has been fairly stable, Mosley-Thompson said. But the new
core from Guliya, along with their other low-latitude ice core records,
suggests that the tropics and sub-tropics may have experienced
considerable climate variability during the last 100,000 years.

Along with Thompson, Mosley-Thompson and Henderson, the research team
included John Bolzan, senior research associate; M.E. Davis, P.-N. Lin
and J. Cole-Dai, all research associates from Ohio State's Byrd Polar
Research Center; T. Yao from the Lanzhou Institute of Glaciology and
Geocryology, Lanzhou, China; J. Beer, Swiss Federal Institute for
Environmental Science and Technology, Dubendorf, Switzerland; and H.-A.
Synal, Paul Scherrer Institute, Zurich, Switzerland.
--------

Contact: Ellen Mosley-Thompson (614) 292-6662;
Thompson.4@osu.edu



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From: Leroy Ellenberger <cle@imr-stl.com>
To: cambridge-conference <cambridge-conference@livjm.ac.uk>
Copies to: "b.j.peiser" <B.J.PEISER@livjm.ac.uk>
Subject: Re: Abrupt climate changes from ~30K to 15K BP
Date sent: Mon, 30 Jun 1997 13:16:58 -0500

One interesting aspect of low latitude glaciers such
as those in China and South America is that each
annual accumulation of snow is marked by a visible
band of dust that settles during the summer. This
is in distinct contrast to high latitude glaciers,such
as in Greenland and Antarctica, where summer dust
accumulation is too sparse to produce a visible band,
although a thickening of dust during the summer can
be detected via instruments that measure micro-particle
concentration. Such annual, summer dust banding is
clearly visible in the photo that accompanied the SCIENCE
paper on Thompson's work on the Dunde glacier in China
that appeared several years ago and also in a photo in
January 1987 National Geographic of a glacier face in
Peru. While it is true that the low latitude glaciers
preserve detailed records of regional climate trends, they
also preserve detailed records of global climate trends
that are consonant with those detected in Greenland
and Antarctica. Thus, the true annual nature of layers
of snowfall in glaciers, distinct from snowfall to snowfall
variations, has been established by glaciologists beyond
all reasonable doubt--perhaps some might say beyond
all possible doubt.
I am grateful to Bob Kobres for bringing this latest
development in glaciology to the attention of the cc-list
readers in such a timely manner, considering the recent
importuning that something might be awry in our ability
to count annual layers in ice cores extracted from glaciers.
What is also awesome to contemplate is the fact that in
the latest cores from Greenland, at the GRIP and GISP
sites, the top-most 80,000+ annual layers can be seen
with the naked eye when thin sections are viewed with
polarized light.

Cheers, Leroy Ellenberger



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From: Leroy Ellenberger <cle@imr-stl.com>
To: cambridge-conference <cambridge-conference@livjm.ac.uk>
Copies to: "b.j.peiser" <B.J.PEISER@livjm.ac.uk>
Subject: IS THE SKY FALLING?: On-Line
Date sent: Mon, 30 Jun 1997 11:37:00 -0500

David Morrison's article of the subject title is now
available on-line at:

<www.csicop.org/si/9705/asteroid.html>

Some may recall preliminary discussion of this article
appeared on the cc-list when the issue of Skeptical
Inquirer first came out about six weeks ago.

I, for one, would be most grateful for comments from
the list readers to be posted on the cc-list.

Cheers, Leroy

--C. Leroy Ellenberger, "vivere est vincere"
http://abob.libs.uga.edu/bobk/velidelu.html
ftp://ftp.primenet.com/pub/lippard/; 9 cle-files
cle@imr-stl.com



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Date sent: Mon, 30 Jun 1997 09:32:06 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: Love thy electronic neighbour!
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

LOVE THY ELECTRONIC NEIGHBOUR!

Despite repeated attempts to prevent inflammatory language on this
open network and to encourage gentlemanly matter-of-fact debate, some
list members appear to have difficulties in restraining their
emotions when faced with controversial thoughts or ideas. Yet it is
in the nature of this network that we will frequently come across
unconventional theories or comments which might even question the
currently held scientific paradigm in a given field of research. I
would therefore like to remind list members that I will no longer
tolerate inflammatory or derogatory language on this net. If
individual members fail to obey these rules of conduct, I might
have no other option as to remove them from this list.

Benny J Peiser



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Date sent: Mon, 30 Jun 1997 09:00:59 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: IMPACT CRATERING RATE
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

MORE ON THE PROBLEM ON HOW TO ASSESS THE IMPACT CRATERING RATE

A.S. McEwen, J. M. Moore, & E. M. Shoemaker:
The Phanerozoic impact cratering rate: Evidence from the farside of the
moon
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, 1997, Vol.102, No.E4,
pp. 9231-9242

The relatively recent (< 1 b.y.) flux of asteroids and comets forming
large craters on the Earth and Moon may be accurately recorded by
craters with bright rays on the Moon's farside. Many previously unknown
farside rayed craters are clearly distinguished in the low-phase-angle
images returned by the Clementine spacecraft. Some large rayed craters on
the lunar nearside are probably significantly older than 1 Ga;
rays remain visible over the maria due to compositional contrasts long
after soils have reached optical maturity. Most of the farside crust has
a more homogeneous composition and only immature rays are visible. The
size-frequency distribution of farside rayed craters is similar to that
measured for Eratosthenian craters (up to 3.2 b.y.) at diameters larger
than 15 km. The areal density of farside rayed craters matches that of
a corrected tabulation of nearside Copernican craters. Hence the presence
of bright rays due to immature soils around large craters provides a
consistent time-stratigraphic basis for defining the base of the
Copernican System. The density of large craters less than similar to
3.2 b.y. old is similar to 3.2 times higher than that of large farside
rayed craters alone. This observation can be interpreted in two ways:
(1) the average cratering rate has been constant over the past 3.2
b.y. and the base of the Copernican is similar to 1 Ga, or (2) the
cratering rate has increased in recent geologic time and the base of
the Copernican is less than 1 Ga. We favor the latter interpretation
because the rays of Copernicus (800-850 m.y. old) appear to be very
close to optical maturity, suggesting that the average Copernican
cratering rate was similar to 35% higher than the average Eratosthenian
rate. Other lines of evidence for an increase in the Phanerozoic (545 Ga)
cratering rate are (1) the densities of small craters superimposed on
Copernicus and Apollo landing sites, (2) the rates estimated from
well-dated terrestrial craters (less than or equal to 120 m.y.) and
from present-day astronomical observations, and (3) the Proterozoic
rate suggested;by the crater record of Australia. The hypothesis most
consistent with several key observations is that the cratering rate
has increased by similar to 2x during the past similar to 300 m.y..

------------------------------------------------------------------------

L. Jetsu: The 'human' statistics of terrestrial impact cratering rate
ASTRONOMY AND ASTROPHYSICS, 1997, Vol.321, No.2, pp.L33-L36 (letter)

The most significant periodicities in the terrestrial impact crater
record are due to the 'human-signal': the bias of assigning integer
values for the crater ages. This bias seems to have eluded the
proponents and opponents of real periodicity in the occurrence of these
events, as well as the theorists searching for an extraterrestrial
explanation for such periodicity. The 'human-signal' should be
seriously considered by scientists in astronomy, geology and
paleontology when searching for a connection between terrestrial major
comet or asteroid impacts and mass extinctions of species.



*

Date sent: Mon, 30 Jun 1997 08:50:21 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: IMPACT CRATER CHAINS
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

IMPACT CRATER CHAINS ON EARTH AND MOON


W. F. Bottke, D. C. Richardson, & S.G. Love:
Can tidal disruption of asteroids make crater chains on the earth and
moon?
ICARUS, 1997, Vol.126, No.2, pp.470-474

Crater chains, presumably formed by weak asteroids or comets stretched
apart by planetary tides, have been tentatively identified on both the
Earth and Moon. By modeling tidal disruption by the Earth and Moon of
'rubble-pile' bodies, we find that the Earth disrupts enough objects
over the last 3.8 billion years to account for one or two lunar crater
chains, but that the reciprocal production rate of terrestrial crater
chains is too low to make any in observable geological history.



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Date sent: Mon, 30 Jun 1997 08:46:19 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: COMETARY DUST
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

DUST TRAILS IN LONG-PERIOD COMETS


P. Jenniskens, H. Betlem, M. deLignie, & M. Langbroek:
The detection of a dust trail in the orbit of an Earth-threatening
long-period comet.
ASTROPHYSICAL JOURNAL, 1997, Vol.479, No.1 Pt1,
pp.441-447

IRAS has detected dust trails in the orbit of short-period comets but
has been unable to detect such trails in the orbit of long-period
comets. We now present observations from the study of a meteor outburst
that identify the event as being due to just that. Ten orbits of meteoroids
were measured during a brief but intense outburst of the alpha
Monocerotid shower that confirm the theory that a trail of dust is
brought occasionally in collision with the Earth by planetary perturbations.
Observations of this event by multiple meteor observing techniques
provide the first direct measurement of the size distribution of dust
in a comet dust trail, the dust density in the trail of a long-period
comet, and a cross section of such a trail in the path of Earth. The
implication for detecting potential Earth-threatening long-period
comets by their meteoric signature is discussed.



CCCMENU CCC for 1997

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