PLEASE NOTE:


*

CCNet 57/2001 - 19 April 2001
-----------------------------


"If such an impact occurred today it could result in hundreds of
millions, perhaps billions, of deaths, mostly through the collapse of
agriculture and subsequent starvation. 800,000 years ago our ancestors,
Homo erectus, were roaming Africa and Southern Asia. Those who survived
the direct blast and firestorm effects of the impact would have had to
endure extremely harsh global conditions for several years. A species that
could control and use fire would have been at a major advantage during
those dark, cold months. This impact may have been a very close call
for the survival of mankind."
--Michael Paine, Meteorite, February 2001


(1) HUMAN RACE 'JUST LUCKY'
    The Times, 18 April 2001

(2) THE NEW THEORY OF EVOLUTION? IT WAS A STROKE OF COSMIC LUCK
    Daily Express, 18 April 2001

(3) SIGNS OF A DEVASTATING ASTEROID IMPACT IN INDOCHINA 800,000 YEARS AGO
    Michael Paine (mpaine@tpgi.com.au)

(4) RESEARCH SHOWS COMET LED TO EARTH'S LARGEST EXTINCTION
    Campus Times, 17 Apirl 2001

(5) WHAT MEDIEVAL WITNESSES SAW WAS NOT BIG LUNAR IMPACT, GRAD STUDENT SAYS
    Ron Baalke <baalke@ZAGAMI.JPL.NASA.GOV>

(6) ASTRONOMERS FIND DISTANT 'DOUBLE PLANET'
    BBC New Online, 18 April 2001

(7) A DISTANT ASTEROID PAIR
    Astronomy.com, 18 April 2001

(8) ASTRONOMERS DEBATE WHAT MAKES A PLANET
    The New York Times, 17 April 2001

(9) CLIMATIC DISASTER MAY HAVE TRIGGERED HUMAN EVOLUTION
    AlphaGalileo, 22 January 2001

(10) DOUBTS ABOUT IMPACT-DRIVEN HUMAN EVOLUTION
     Steve Drury <s.a.drury@open.ac.uk>

(11) 90 PERCENT OF WHAT? AND SOME OTHER COMMENTS
     Duncan Steel <D.I.Steel@salford.ac.uk>

(12) BIOGEOGRAPHIC AND CLIMATIC BASIS FOR A NARRATIVE OF EARLY HOMINID
EVOLUTION
     BROMAGE TG, SCHRENK F

(13) PUNCTUATED EQUILIBRIUM: HUMAN EVOLUTION & NATURAL CATASTROPHES
     Ambrose SH

(14) DARWINISM, GRADUALISM AND UNIFORMITARIANISM
     Reif WE

(15) NONLINEAR RESPONSE OF BIOTIC SYSTEMS TO COSMIC IMPACTS
     Plotnick RE, Sepkoski JJ


===============
(1) HUMAN RACE 'JUST LUCKY'
 
From The Times, 18 April 2001
http://www.thetimes.co.uk/article/0,,2-116327,00.html
 
BY MARK HENDERSON, SCIENCE CORRESPONDENT
 
MODERN human beings might have outlasted relations such as the Neanderthals
not because of genetic advantages, but by a slice of "cosmic luck",
according to two scientists.

A theory developed by a British social anthropologist and an Australian
astronomer holds that Homo sapiens has been extremely lucky not to have been
wiped out by an asteroid impact - and that other hominid species might not
have been so fortunate.

The idea challenges the accepted explanation for human evolution that Homo
sapiens was simply better adapted than other early human-like species and
that modern man came to dominate through natural selection.

Benny Peiser, of Liverpool John Moores University, and Michael Paine, of the
Planetary Society in Australia, calculated the probability of asteroid
impacts over five million years that could have had evolutionary
consequences.

They worked out that more than 20 devastating impacts would have occurred
during that period, and that plenty of species of hominids were probably
killed off. Mankind, they argue, has simply been lucky.

"The reason that Homo sapiens has survived has little to do with the
explanations given by neo-Darwinists," Dr Peiser said. "It is sobering to
realise that we are alive due to cosmic luck rather than our genetic
make-up. After all, the populations of hominids and early modern humans were
extremely small. Had any of these impacts occurred in the proximity of these
population groups, we might also have gone the way of the dodo."

Chris Stringer, head of the human origins group at the Natural History
Museum in London, said that the theory sounded far-fetched. "It would be
hard to narrow down an event that, for example, would have affected the
Neanderthals in Europe but not the Cro-Magnons, the modern humans who
overlapped with them," he said. Recent studies of fossil evidence have
suggested more gradual evolutionary changes in hominid species than is
assumed by Dr Peiser's study. "It is no longer true to say that the fossil
record shows abrupt change," Professor Stringer said.
 
Copyright 2001 Times Newspapers Ltd.

==============
(2) THE NEW THEORY OF EVOLUTION? IT WAS A STROKE OF COSMIC LUCK

From Daily Express, 18 April 2001

Humans came to dominate the planet by cosmic chance, new research has
revealed. Mankind's rise to the top of the evolutionary tree had less to do
with superior intelligence and more to do with being in the right place at
the right time, two experts claimed yesterday.

Our ancestors only triumphed because, unlike more than a dozen pre-historic
species, they were fortunate enough to avoid being wiped out by an asteroid
or comet.

The theory contradicts Darwinian doctrine that suggests it is the strongest
who survive.

Social anthropologist Dr Benny Peiser, of Liverpool John Moores University,
said: "It is sobering to realise we are alive due to cosmic luck rather than
our genetic make-up." Dr Peiser, who conducted his research with impact
expert Michael Paine, calculated the number of asteroids and comets striking
the earth in the last five million years.

Using a generally accepted "impact rate" they found all Earth species have
endured a battering from space. In that time there would have been 108
"severe regional" events, causing devastation over a an area the size of a
large country.

One known example was two million years ago when a two-kilometre wide
asteroid struck the Southern Ocean south-west of Chile.

Mr Paine, of the Planetary Society in Australia, said: "If the collision had
occurred a few hours early, southern Africa might have been wiped out, along
with our ancestors."

Copyright 2001, Daily Express

===============
(3) SIGNS OF A DEVASTATING ASTEROID IMPACT IN INDOCHINA 800,000 YEARS AGO

by Michael Paine (mpaine@tpgi.com.au)

Published as "Source of the Australasian Tektites?" in Meteorite, February 2001
http://www.meteor.co.nz/

Introduction

One of the hurdles to increased public awareness about the hazard from asteroid and comet impacts is the scarcity of hard evidence of recent major impacts. A report in the March 2000 issue of Science therefore caught my attention. An archaeological excavation in South China, near the town of Bose found stone tools in sediments containing Australasian tektites (Yamei et al 2000). The researchers also found evidence of an episode of woody plant burning, widespread forest destruction and exposure of "cobble outcrops" when soil was scoured away. They suggested that this destruction was initiated by the event that generated the tektites - namely a major impact in Indochina (Vietnam, Laos, Thailand and Cambodia). This is still speculative (and controversial) but if, proven, would add an important piece to the jigsaw puzzle that should eventually reveal the source of the Australasian tektites. It could help determine the magnitude of the explosive event.

This article records my attempts to find out more about the Australasian tektite event and some speculation on the global consequences of the event.

Australasian tektites

Most tektites are glass beads or balls that are produced by ejection of material fused by large asteroid or comet impacts. For years scientists have been investigating the 'Australasian Tektite Strewn Field' that stretches from China to Australia, as well as large parts of the eastern Indian Ocean. Evidence points to an impact some 800,000 years ago in Indochina (Schmidt et al 1993, Hartung and Koeberl 1994, Schnetzler and Mchone 1996, Howard et al 2000, Glass 1999). However, the source crater is proving very elusive. Working on the geographic variation in tektite concentration Glass and Pizzuto (1994) estimated the diameter of the impact crater to be between 32 and 114 kilometres. They made no assertions about the impactor's characteristics. If it was a stony asteroid travelling at a speed of 22km/s then its diameter would be between 2 and 5 km (see Appendix). Earlier estimates using iridium concentrations suggested a crater diameter less than 20km (Schmidt, Zhou and Wasson1993) but the later estimates are probably more reliable.

It seems remarkable that such a large "fresh" crater has not been found but a comparison of known impact craters with the expected cratering rate suggests that many ancient craters have not been found (Lewis 1999). It is possible that the Indochinese crater has been totally eroded away or covered by deep sediments - perhaps in the Mekong delta. However, political/military sensitivities in the area have reportedly hampered geological expeditions. Hartung and Koberl (1994) studied a region in northern Cambodia near the Tonle Sap lake (also known as Tonle Sab). They raised the possibility that the 100 km by 35 km lake could be associated with the crater. They presented arguments for and against the hypothesis and concluded "many aspects of the Tonle Sap lake and basin are consistent with the hypotheses that it is the source crater...but further research is needed".

Schnetzler and Mchone (1996) studied several regions in Laos, looking for the source of the tektites. They concluded "none showed obvious evidence of extraterrestrial impact [crater]". Howard et al (2000) studied sites in NE Thailand near the town of Khorat, looking for environmental effects of a major impact. They found petrified trees with trunks up to 2 metres in diameter "shattered, branchless, snapped, uprooted and burnt to the core" together with evidence of catastrophic floods. They report that the study location is "about 400km west of the area where layered tektites are most abundant, this area is believed by many to be close to the impact centre".

Povenmire, Liu and Xianlin (1999) report on several new finds of Australasian tektites near the Bose region in China. Combined with unconfirmed references to tektites some 1000km further north in Ganzu Province, they suggest that the total area of the Earth's surface covered by this strewn field may be in excess of 30%. "The Australasian event must have been much larger than previously supposed. This leads us back to a very basic question and that is, where is the 100km crater?" Dass and Glass (1999) examined mineral inclusions in Muong-Nong type Australasian tektites and reported that the preliminary data were consistent with a source crater in southern Laos or adjacent area. Subsequently Glass (1999 and 2000) reported on further investigations of zircons in the tektites. He noted that additional studies were needed to define the southern geographical limit of shock metamorphism within the tektites and therefore the location of the source crater (based on other strewn fields, Glass assumes that shock metamorphism in tektites increases with distance from the source crater).

Regional environmental effects of an impact

Considerable research has been done in recent years into the environmental consequences of major impacts (Toon et al 1997). Most of this work has involved computer modelling. Although data from major impact events is gradually becoming available (for example - studies of the Chicxulub cratering event and the impact of Comet Shoemaker-Levy 9 with Jupiter) the modelling should still be regarded as somewhat speculative.

The appendix summarises the potential environmental effects of impacts by large asteroids and comets. Estimates of damage are given for 1, 2, 5 and 10 km stony asteroids (caution: at this stage there is no reason to assume the Indochinese impactor was a stony asteroid. Also it may have had an unusually shallow trajectory).

Implications of the Bose destruction

Assuming the impact site for the Indochinese impact event was in the vicinity of northern Cambodia then Bose is about 1200 km to the north. An impact by a stony asteroid at least 5 km in diameter would therefore be required to produced the observed forest destruction at Bose. This is based on the estimate that such an impact would produce a blast wave (1 psi overpressure) sufficient to knock down trees 1100 km from the impact. It is stressed that further research is needed to precisely date the impact event and the forest destruction at Bose and to link the events in order to substantiate this suggestion.

An impact this size would produce a transient crater 40 km across that would slump to form a ringed structure 100 km across. This is in agreement with Glass and Pizzuto's estimate, based on tektite distribution.

The suggestion that Bose forests were ignited by ballistic debris (in effect, radiant heat from millions of meteors - Toon 1997) supports this hypothesis. Such an effect would cover a radius of 5000 km for a 5km asteroid impact but is limited to about 600 km in the case of a 2 km asteroid. Note, however, that this region is subject to frequent devastating forest fires so a link to the impact event may be tenuous. An alternative to ignition from ballastic debris effects is the possibility that the impactor followed a very shallow trajectory that would have subjected a strip of land to intense radiant heat prior to impact (Lewis 1999).

Regional extinctions of plant and animal life could be expected but this is a region that could be expected to quickly recover through regeneration and migration.

A modern day analogy

Putting the speculative Indochina impact event in perspective, if the impact site had been San Fransisco then:

* the crater would have been as big as San Fransisco Bay,

* the giant Redwoods in Sequoia National Park, some 400 km to the east, would have been   shattered and burnt (equivalent to the region studied by Howard et al).

* 1200 km further north in Washington State the Mt St Helens region would have seen   destruction equivalent to the volcanic explosion in 1980 (distance comparable to the Bose   region).

Global environmental effects of the impact

If a 5km diameter stony asteroid did strike Indochina 800,000 years ago then dust, soot and sulfur oxides would have spread around the globe within days and turned day into night. Freezing conditions would have occurred, in even tropical locations. It would have been months, possibly years, before photosynthesis could start again. Adding to the woes of surviving life, the ozone layer would have been destroyed so, once the skies cleared, UV radiation would become a deadly hazard. Moderate greenhouse heating may have occurred once the skies cleared. Irrespective of greenhouse heating, weather patterns would have been severely disrupted for years leading to extreme droughts and floods.

Despite the severe effects on life resulting from the environmental extremes it seems that there would be little long-lasting evidence of this event around the globe. Depending on the composition of the impactor and the characteristics of the impact, a layer of iridium and other indicators of an impact should show up in ice cores, ocean sediments, lake sediments and fossil coral reefs (Schmidt 1993). A possible problem is that this is a very difficult period to date, being beyond the range of many dating techniques but not old enough for others (Dr Peter Haines, University of Tasmania -personal correspondence). The tektite event has been variously dated at between 770,000 and 800,000 years ago. In a recent publication Lee and Wei (2000) used two deep sea cores to derive an age of 793,000 years. They also estimate a crater diameter between 90 and 116km.

The very severe cold spell was probably too short to show up in paleoclimate records (and might have been countered by a brief period of greenhouse warming). Data recently presented by Rutherford and D'Hondt (2000) in relation to glacial cycles over the past 3 million years do not appear to show any pronounced temperature fluctuations 800,000 years ago. D'Hondt cautioned that although the shift to 100,000 year glacial cycles is widely said to have occurred about 700 to 800 thousand years ago it actually began about 1.5 million years ago (personal correspondence). Similarly, there do not appear to be any signs of the presumed destruction of surface life due to the temporary loss of the ozone layer.

If such an impact occurred today it could result in hundreds of millions, perhaps billions, of deaths, mostly through the collapse of agriculture and subsequent starvation (Paine 1999 and Garshnek 2000, Steel 2000). 800,000 years ago our ancestors, Homo Erectus, were roaming Africa and Southern Asia. Those who survived the direct blast and firestorm effects of the impact would have had to endure extremely harsh global conditions for several years. A species that could control and use fire would have been at a major advantage during those dark, cold months.

This impact may have been a very close call for the survival of mankind.

Acknowledgements

Thank you to the following people for providing advice and comments: Andrew Glikson, Charles Schnetzler, Steven D'Hondt, Alan Harris, David Morrison, Jay Melosh and Peter Haines.

References

Chao, E. C. T. (1993) Comparison of the Cretaceous-Tertiary boundary
impact events and the 0.77-Ma Australasian tektite event : relevance to mass
extinction, U.S. Geological Survey bulletin 2050, Denver.

Dass J.D. and Glass B.P. (1999) 'Geographic variations in concentration of
mineral inclusions in
Muong Nong-type Australasian tektites: implications regarding the location
of the Australasian
tektite source crater', 30th Annual Lunar and Planetary Science Conference,
Houston, March 1999.

Garshnek V., Morrison D. and Burkle F. (2000) 'The mitigation, management
and survivability of
asteroid/comet impact with Earth' J Space Policy Vol 16 (2000) 213-222.

Gersonde R., Kyte F.T., Bleil U., Diekmann B., Floress J.A., Gohl K., Grahl
G., Hagen R., Kuhn
G., Sierros F.J., Volker D., Abelmann A. and Bostewick J.A. (1997)
'Geological record and
reconstruction of the late Pliocene impact of the Eltanin asteroid in the
Southern Ocean', Nature
No.390, 357-363, 27 Nov 1997.

Glass B.P. and Pizzuto J.E. (1994) 'Geographic variation in Australasian
microtektite
concentrations: Implications concerning the location and size of the source
crater', J of Geophysical

Research vol 99 no.E9, 19075-19081, Sept 1994 (abstract only)
Glass B.P. (1999) 'Muong Nong-type Australasian tektites: implications
regarding the parent
material and source area', Ninth Annual V.M. Goldschmidt Conference,
Massachusetts, August
1999.

Glass B.P. (2000) 'Relict zircon inclusions in Muong Nong-type Australasian
tektites: implications regarding the location of the source crater',
Proceedings of 31st Lunar and Planetary Science Conference, March 2000.

Howard K.T., Bunopass S., Burret C.F., Haines P.W. and Norman M.D. (2000)
'The 770KA tektite
producing impact event: evidence for distal environmental effects in NE
Thailand', Proceedings of
31st Lunar and Planetary Science Conference, March 2000.
http://www.lpi.usra.edu/meetings/lpsc2000/

Harington C.R. - editor (1992) The year without a summer? world climate in
1816. Canadian
Museum of Nature, Ottawa 1992. Includes research on Tambora volcanic
explosion.

Hartung J. and Koberl C. (1994) 'In search of the Australasian tektite
source crater: the Tonle Sap hypothesis', Meteoritics.

Koeberl C. and B.P. Glass (2000) 'Tektites and the Age Paradox in
Mid-Pleistocene China',
Science, 289, No 5479, 28 Jul 2000, p. 507. See also the response by Potts
et al.

Kring D.A., Melosh H.J. and Hunten D.M (1995) 'Possible climate
perturbations produced by
impacting asteroids and comets', Meteoritics Vol 30, No.5 530.

Larick R. and Ciochon R. (1996) 'The African emergence and early asian
dispersals of the Genus
Homo', American Scientist, Nov-Dec 1996.
(http://www.amsci.org/articles/96articles/Larick.html)

Lee M.Y. and Wei K.Y. (2000) 'Australasian microtektites in the South China
Sea and West
Philippine Sae: implications for age, size and location of the impact
crater', Meteoritics and
Planetary Science,vol 35, no. 6 1151-1155.

Lewis J.S. (1999) Comet and asteroid impact hazards on a populated Earth,
Academic Press.
Includes impact simulation software.

Melosh H. J. (1997) 'Multi-ringed revelation', Nature 390, 439 - 440 (1997)
Macmillan Publishers
Ltd.

Paine M. (1999) 'Asteroid impacts: the extra hazard due to tsunami', Science
of Tsunami Hazards,
Vol 17, No.3 (1999). Includes estimates of fatalities from impacts. See
http://www1.tpgi.com.au/users/tps-seti/spacegd7.html

Povenmire H., Liu W. and Xianlin l. (1999) 'Australasian tektites found in
Guangxi Province,
China', 30th Annual Lunar and Planetary Science Conference, Houston, March
1999.

Rutherford S. and D'Hondt S. (2000) 'Early onset and tropical forcing of
100,000 year Pleistocene
glacial cycles', Nature, Vol 408, 72-74 (2000) Macmillan Publishers Ltd.

Schmidt G., Zhou L and Wasson J. (1993) 'Iridium in sediments containing
large abundances of
Australasian microtektites from DSDP hole 758B in the Eastern Indian ocean
and from DSDP hole
769A in the Sulu Sea', Proceedings of 24th Lunar and Planetary Science
Conference

Schmidt G. and Wasson J.T. (1993) 'Masses of the impactor, the Australasian
tektites, and size
estimates of the main source crater', Meteoritics, vol 28 no.3, 430, Jul
1993.

Schnetzler C.C. and Mchone J.F. (1996) 'Source of the Australasian tektites:
Investigating possible impact sites in Laos', Meteoritics and Planetary
Science, no.31 73-76, 1996.

Steel D. (1995) Rogue asteroids and doomsday comets, Wiley & Sons.

Steel D. (2000) Target Earth, Readers Digest Association Inc.

Toon O., Morrision D., Turco R.P. and Covey C. (1997) 'Environmental
perturbations caused by the
impacts of asteroids and comets', Reviews of Geophysics, vol 35, no.1,
41-78, Feb 1997.

Yamei H., Potts R., Baoyin Y., Zhengtang G., Deino A., Wei W., Clark J.,
Guangmao X and ,
Weiwen H. (2000) 'Mid-Pleistocene Acheulean-like stone technology of the
Bose Basin, South
China', Science, vol 287 1622-1626.

Vrba E. - editor (1995) Paleoclimate and evolution, with emphasis on human
origins, Yale
University Press.

==============
(4) RESEARCH SHOWS COMET LED TO EARTH'S LARGEST EXTINCTION

From Campus Times, 17 Apirl 2001
http://news.excite.com/news/uw/010417/tech-74

From Staff Reports
Campus Times
U. Rochester

(U-WIRE) ROCHESTER, N.Y. -- Recent research suggests that an asteroid or
comet that collided into Earth 251 million years ago was a key factor in the
cascade of events that led to the "Great Dying," the biggest extinction in
Earth's history.

The asteroid, similar to the one that killed the dinosaurs, is estimated to
have been six to 12 kilometers wide and would have caused considerable
damage.

The research, conducted by a group of researchers that included scientists
from UR, University of Washington, NASA and New York University, was
published in a February issue of Science magazine.

"The impact of a bolide of this size releases an amount of energy that is
basically about one million times the largest earthquake recorded during the
last century. It was like a magnitude 12.0 earthquake on the Richter scale,"
said Robert Poreda, UR professor of earth and environmental sciences.

COSMIC STOWAWAYS

Much of the evidence supporting these findings were in the form of cosmic
stowaways, such as helium and argon molecules, which were incased in carbon
molecules called buckyballs.

The gaseous molecules originated in other parts of the universe and traveled
to Earth through the hardy buckyballs as part of the impact from the
asteroid.

By conducting measurements, Poreda, post-doctoral associate Andrew Hunt and
researchers from the University of Washington proved that the ratios of the
gas molecules were indicative of meteorite and comets that must have been
formed in space.

"[It is] unlikely that the collision was directly responsible for the
extinction," Washington researcher Luann Becker said in a press release.

"Rather, it may have triggered a series of events, such as the volcanic
activity and changes in sea level and climate, that wiped out more than 90
percent of marine animals and about 70 percent of land vertebrates," she
said.

This recent discovery is merely another step in the ongoing research in this
area.

In 1996, Becker, Poreda and other colleagues discovered that buckyballs, or
fullerenes, near Ontario came from space nearly two billion years ago and
arrived on Earth intact.

They also showed that even more complex carbon molecules had survived an
impact from space at the same time as the impact that wiped out the
dinosaurs

ORGANIC COMPOUNDS

Their papers have demonstrated how comets and meteorites can deliver organic
compounds to Earth, further fuels the theory that early life on Earth could
have been instigated by complex carbon compounds from space.

It is possible that the carbon cages could have provided a skeleton for the
other molecules that were carried to Earth as well.

Nonetheless, Poreda, who has been doing research in this area for
approximately seven years, feels that there is much more to be explored in
these areas.

"There are other major mass extinctions over the past 500 million years, and
one of the things to provide more closure is to look for impact-related
materials at the boundaries, or more clear-cut evidence for the association
between these major extinctions," he said.

He also intends to delve more into the fullerenes' roles in the origin of
the Earth.

He will investigate the possibility that the fullerenes had the ability to
contain noble gases, which would have caused them to be some of the major
carriers of the Earth's early atmosphere.

"We are trying to clarify whether fullerenes could provide carrier phases
for the gases like helium, neon, and argon. Did they come from Earth's
interior or were they a result of bombardment?" Poreda said.

SKEPTICISM

Along the way, though, there has been some skepticism with respect to the
scientists' research. Because of its abstractness, many people have not been
willing to accept the theories, which contradict conventional wisdom in many
ways.

However, Poreda remains optimistic.

"It is exciting to get vindication because people didn't really understand
what we were doing, and it was frustrating because they didn't understand,"
he said.

We think we have much stronger evidence now, so it's gaining more
acceptance, and this is gratifying," he continued. "We have a long way to
go, though, before we get all the pieces of the puzzle put together."

(C) 2001 Campus Times via U-WIRE

===========
(5) WHAT MEDIEVAL WITNESSES SAW WAS NOT BIG LUNAR IMPACT, GRAD STUDENT SAYS

From Ron Baalke <baalke@ZAGAMI.JPL.NASA.GOV>

http://uanews.opi.arizona.edu/cgi-bin/WebObjects/UANews.woa/wa/SRStoryDetails?ArticleID=3561

Lori Stiles
University of Arizona News Services
April 18, 2001

WHAT MEDIEVAL WITNESSES SAW WAS NOT BIG LUNAR IMPACT, GRAD STUDENT SAYS

The idea that what humans witnessed and chronicled in 1178 A.D. was a major
meteor impact that created the 22-kilometer (14-mile) lunar crater called
Giordano Bruno is myth, a University of Arizona graduate student has
discovered.

And this should be welcome news for those worried by Deep Impact movie
scenarios.

The idea that 12th century people saw the impact that created a lunar crater
more than 10 times as wide as Meteor Crater in northern Arizona has been
popular since it was first proposed 25 years ago. But it doesn't hold up
under scientific scrutiny, said Paul Withers of the UA Lunar and Planetary
Laboratory.

Such an impact would have resulted in a blinding, blizzard-like, week-long
meteor storm on Earth - yet there are no such accounts in any known
historical record, including the European, Chinese, Arabic, Japanese and
Korean astronomical archives, Withers said. He reports the analysis and
other tests of the hypothesis in this month's issue of Meteoritics and
Planetary Science.

The dramatic passage in question appears in the medieval chronicles of
Gervase of Canterbury.

About an hour after sunset June 18, 1178 A.D., a band of five eyewitnesses
watched as the upper horn of the bright, new crescent moon "suddenly split
in two. From the midpoint of this division a flaming torch sprang up,
spewing out . . . fire, hot coals and sparks. . .The body of the moon, which
was below writhed. . .throbbed like a wounded snake." The phenomenon
recurred another dozen times or more, the witnesses reported.

A geologist suggested in 1976 that this account is consistent with the
location and age of Giordano Bruno, the youngest crater of its size or
larger on the moon.

A one-to-three kilometer wide (a half-mile to almost 5-mile wide) meteor
blasted Giordano Bruno into the northeast limb of the moon. Such an impact
on the Earth would be "civilization threatening," causing regional
devastation to global climatic catastrophe - so it is important to know if
such an event happened on the moon less than a millennium ago, Withers
noted.

The impact would have launched 10 million tons of ejecta into the Earth's
atmosphere in the following week, previous studies have shown, Withers said.
In the Meteoritics article, Withers reports his calculations on the
properties of the subsequent meteor storm.

"I calculate that this would cause a week-long meteor storm potentially
comparable to the peak of the 1966 Leonids storm." Ten million tons of rock
showering the entire Earth as pieces of ejecta about a centimeter across
(inch-sized fragments) for a week is equivalent to 50,000 meteors an hour.

"And they would be very bright, very easy to see, at magnitude 1 or
magnitude 2. It would have been a spectacular sight to see! Everyone around
the world would have had the opportunity to see the best fireworks show in
history, " Withers said.

Yet no vigilant 12th century sky watcher reported such a storm.

So what did the witnessess see that the Canterbury monk recorded?

"I think they happened to be at the right place at the right time to look up
in the sky and see a meteor that was directly in front of the moon, coming
straight towards them," Withers said. This idea was strongly suggested by
others in a 1977 scientific paper.

"And it was a pretty spectacular meteor that burst into flames in the
Earth's atmosphere- fizzling, bubbling, and spluttering. If you were in the
right one-to-two kilometer patch on Earth's surface, you'd get the perfect
geometry," he said. "That would explain why only five people are recorded to
have seen it.

"Imagine being in Canterbury on that June evening and seeing the moon
convulse and spray hot, molten rock into space, " Withers added. "The
memories of it would live with you for the rest of your life."

Contact:
Paul Withers,  UA planetary sciences
520-621-1507, withers@lpl.arizona.edu

==========
(6) ASTRONOMERS FIND DISTANT 'DOUBLE PLANET'

From the BBC New Online, 18 April 2001
http://news.bbc.co.uk/hi/english/sci/tech/newsid_1283000/1283621.stm

By BBC News Online science editor Dr David Whitehouse

Astronomers have discovered a strange pair of objects orbiting each other at
the edge of the Solar System.

They believe that the lumps of rock and ice, a few hundred miles in
diameter, may be a pair of small planets.

But other experts disagree, saying the bodies are too small to be classified
as planets.

The pair exists among a group of at least 70,000 objects, known as the
Kuiper Belt, that circle the Sun, extending beyond the most distant planet
Pluto.

Is this a pair of planets?
 
In January, astronomers attempted to find a specific object among this ring
of comet-like objects. This body, designated 1998 WW 31, was first seen a
few years ago.

But when Christian Veillet and colleagues from the Canada-France-Hawaii
Telescope looked at their images of the object, it appeared double. Further
observations made on subsequent nights confirmed that the object was in fact
a twin.

Furthermore, images of the body taken by accident during observations of
other objects and tracked down in astronomical archives also revealed it to
be either double or elongated in shape.

Astronomers say that there are similarities between the appearance of the
pair, and that of Pluto and its large moon Charon.

Some researchers believe that Pluto is too small and unusual to be a true
planet. They think that Pluto and Charon should be regarded as the largest
Kuiper Belt objects, and the first known example of a double planet.

The new pair may be the second known example of this, they say.

Copyright 2001, BBC

=============
(7) A DISTANT ASTEROID PAIR

From Astronomy.com, 18 April 2001
http://www2.astronomy.com/Content/Dynamic/Articles/000/000/000/399tecig.asp

Astronomers have realized that an object beyond the orbit of Neptune is
actually a pair of objects.

by Vanessa Thomas

Pluto is the best known and first solar system object discovered beyond the
orbit of Neptune. Since 1992, more than 350 other Trans-Neptunian Objects
(TNOs) have been found. Now, a team of astronomers has found the first TNO
other than Pluto with a satellite.

In December of last year, astronomers Christian Veillet and Joshua Shapiro
from the Canada France Hawaii Telescope (CFHT) staff and Alain
Doressoundiram of the Observatoire de Paris used the 3.6-meter CFHT to
observe 1998 WW31. The team noticed an elongated shape to the object, and
after examining it further, realized that there were actually two separate
objects.

Although unlikely, Veillet knew that the two objects could be unrelated and
just happened to be in the same area when he and his colleagues took a look.
"It would be strange," he said, "but stranger things have been seen in
space." There was no relative motion between them over the two nights they
were observed, but that was not enough time to determine whether or not the
objects were linked.

To find the answer to this question, Veillet obtained images of 1998 WW31
taken by two other astronomers using the CFHT in January 2000. After close
scrutiny, he found that, although harder to see, two distinct objects were
visible in those images as well. This evidence that the two objects remained
close to each other over nearly a year proves they are bound together.

From the observations so far, Veillet's team estimates that the two bodies
are separated by about 40,000 kilometers. The secondary object is dimmer
than the primary, but not significantly. Pluto's moon Charon is about half
the size of the planet, and Veillet says the asteroid and its satellite may
resemble the more famous pair.

About 45 astronomical units from the sun, 1998 WW31 and its moon lie beyond
Pluto and take about 300 years to complete one solar orbit. With additional
observations, astronomers will learn more about the physical properties of
the distant pair and the relationship between the two objects.

For more information, please see Christian Villet's site at
http://cfht.hawaii.edu/~veillet/WW31.html about the discovery.

Copyright 1996-2001 Kalmbach Publishing Co. 

=============
(8) ASTRONOMERS DEBATE WHAT MAKES A PLANET

From The New York Times, 17 April 2001
http://www.nytimes.com/2001/04/17/science/17PLAN.html

By JOHN NOBLE WILFORD

By the simplest definition, a planet is a large object that orbits a star.
But the universe, it seems, is hardly simple, and astronomers have lately
been observing things that resemble planets but are drifting freely in
space, beyond the gravitational embrace of any star.

Last year, two groups of astronomers reported detecting a large number of
"free-floating planets" in the Orion Nebula. At an astronomy meeting in
Cambridge, England, this month, one of the groups announced that new
infrared observations had confirmed the existence of at least 20 such
objects in Orion, an active star- forming region more than 1,000 light-
years from Earth.

Dr. Philip Lucas of the University of Hertfordshire and Dr. Patrick Roche of
Oxford University reported the detection of extremely hot water vapor in the
objects, which they said confirmed that the objects are young and
planetlike.

The faintest of the objects, the astronomers said, appear to be the size of
large planets, between 5 and 13 times as massive as Jupiter. They could be
detected by the United Kingdom Infrared Telescope on Mauna Kea in Hawaii
only because they are young and still warm.

Other observations, including those by the Hubble Space Telescope, have
produced evidence that such objects, too small to be stars, yet larger than
most planets and independent of any stellar host, may be a fairly common
phenomenon. But are they planets? That is a question that has astronomers
taking sides in often heated debate.

Dr. Mark McCaughrean, of the Astrophysics Institute in Potsdam, Germany,
complained of the "unfortunate continued use of the word `planet' where it's
unwarranted."

It is not just a question of nomenclature, but of formation processes.

In an article to be published soon in The Astrophysical Journal (Letters),
Dr. Alan P. Boss of the Carnegie Institution in Washington theorized certain
conditions under which the same processes of stellar creation could produce
small, free-floating objects as small as one Jupiter mass. Jupiter's mass is
318 times as great as Earth's.

Such objects with masses below 13 Jupiter masses, Dr. Boss suggested, would
not be planets because of the way they formed. They could more appropriately
be termed sub-brown dwarfs, neither planet nor star but a new class of
in-between objects.

A planet is assumed to form out of the rocky material and gas left in an
orbiting disk around a new star. If these objects were formed in that way,
scientists must figure out how they were thrown out of their orbits around a
star.

A star emerges from the collapse of a heavy molecular cloud. When it exceeds
a mass 75 times that of Jupiter, it is big enough to be a full- blown star
powered by thermonuclear forces. Lesser objects that are formed this way,
essentially failed stars, are called brown dwarfs, because their feeble
energies give off little light.

So if these newly discovered free- floating objects were indeed formed like
a star or a brown dwarf, from a gas cloud in space, then it is misleading to
call them planets, Dr. McCaughrean said. He joined a number of astronomers
who said they preferred the name sub-brown dwarf.

Dr. McCaughrean said he suspected the motives for using the term planet.
"Planets are special to us as humans," he said. "We live on one, perhaps
there's extraterrestrial life on other planets. By saying `planet,' you can
raise enormous public interest."

Other scientists cautioned that it was premature to coin new names and more
classifications for the objects. Whatever the outcome of the debate, Dr.
Roche said, the study of these strange objects "can aid our understanding of
the star-formation process, which is one of the major mysteries in
astronomy."

Copyright 2001 The New York Times Company
 
==========
(9) CLIMATIC DISASTER MAY HAVE TRIGGERED HUMAN EVOLUTION

From AlphaGalileo, 22 January 2001
http://www.alphagalileo.org/ReadNotice.cfm?releaseid=5396

Mr Michael Warwicker
University of Newcastle upon Tyne
0191 222 7850
mick.warwicker@ncl.ac.uk 
  
Did climate change trigger human evolution?

Researchers examining deep-sea sediments off the coast of Namibia, West
Africa, have found evidence that global cooling of 10 degrees Celsius has
occurred since 3.2 million years ago - five times greater than was
previously believed. The discovery adds weight to the theory that climate
change played a significant part in the evolution of early humans.

Dr Jeremy Marlow, of Newcastle University's Department of Fossil Fuels and
Environmental Geochemistry, who led the team of English, American and German
scientists, said: 'There have been arguments for many years about whether
the emergence of our ancestors was linked to climate change. By looking at
the molecular fossils of microscopic marine algae we began to discover
evidence of a 10 degree fall in temperature in the region of Africa where
much of the early human fossil evidence has been discovered.

'We didn't believe it at first but further tests kept producing similar
results until we had to conclude that temperatures really had decreased so
dramatically.'

The scientists, from the Universities of Newcastle, Durham, California and
Bremen, found that cooling was particularly rapid about 2 million years ago,
at the time when the first ancestors of modern humans emerged in
sub-tropical southern Africa.

The research also sheds new light on the mechanisms that may cause climate
change. By examining the rate of sediment deposition and the levels of
organic carbon within the sediments, the researchers obtained evidence of a
well-defined cycle in which a cooling atmosphere causes increased upwelling
of nutrient-rich deep waters in specific parts of the oceans leading to
increased biological uptake of carbon dioxide from the atmosphere, which
then cools further, causing more upwelling and uptake of carbon dioxide.

This mechanism took hundreds of thousands, or even millions of years to have
an effect on climate but could be reversed far more rapidly through the
burning of this type of locked-up carbon as fossil fuels, said Dr Marlow.
 
Notes for Editors
This press release is based on an article, Upwelling Intensification As Part
of the Pliocene-Pleistocene Climate Transition, published in the American
journal, Science (ref 290: 2288-2291.) However, the article in Science
concerns itself with factual findings and does not discuss the implications
for human evolution. No press release has been issued by Science.

Peer reviewed publication and references
Science 290: 2288-2291 (see also Notes for Editors)

============================
* LETTERS TO THE MODERATOR *
============================

(10) DOUBTS ABOUT IMPACT-DRIVEN HUMAN EVOLUTION

From Steve Drury <s.a.drury@open.ac.uk>

Dear Benny

Accepting the inevitability that Earth is struck by extraterrestrial objects
and that there are statistics that give pointers to impacts in terms of
energy and frequency, I feel that there is a long way to go in assigning
speciation (as opposed to general mass extinctions) to external causes.
Speciation among our ancestors is particularly fraught with difficulty,
because of the blurred record.

It is blurred in several ways:

1.  By the tiny number of fossils

2.  By the dates assigned to those fossils

3.  By the significance assigned to their morphology by different
palaeoanthropologists - there are "lumpers" and "splitters"

4.  By the total lack of knowledge about the interplay between physiology,
culture and social interaction, as regards what constituted "fitness" in
natural selection. This sets our own record apart from those of other
species, as does the uniquely wide dispersion of hominids throughout the
"Old World" from about 1.8 Ma.

Evolutionary bottlenecks are indeed implied by extant human genetics - mtDNA
and Y-chromosome data - at ca 200 ka and 70 ka respectively. Beyond that
there is simply not a hint. The cultural and morphological stasis of H.
erectus for 1 Ma (represented by the greatest number of fossils and
artifacts before about 400 ka) could be read as "evidence" for a lack of
such bottlenecks in the 1.4 to 0.4 Ma period.

Using impact statistics is a means of assessing the probabilities of
extraterrestrial events over various time spans, but that does not allow any
kind of prediction of precisely when events of different magnitudes might
have taken place. That only emerges from evidence in the form of craters
which have been dated precisely, which are thin on the ground, despite
discoveries of
geologically young craters.

The record of environmental change at the global level lies in the oxygen
and carbon isotope time series from ocean-floor sediments, supplemented by
polar ice-core records since about 425 ka.  This has a precision of better
than +/- 200 years for the last 125 ka, degrading to +/- 4 ka at the
Oligocene-Miocene boundary (~23 Ma ago). The record is indeed "punctuated"
by major climatic shifts (about 50 over the last 2.5 Ma) and a very large
number of lesser ones in the high-precision time series since 425 ka. The
idea that these time series stem from variations in solar input modulated by
changing orbital obliquity, axial tilt and precession, which are conditioned
by oceanographic and atmospheric factors, is probably the most impregnable
in the Earth sciences, simply because of the quality of the data and their
analyses. While there may be climatic events that buck this model, they do
not have the amplitude to interfere with it.

Because the record of human ancestry is so patchy no-one to my knowledge has
seriously considered linking speciation to these known climatic events,
except in the most general way (eg de Menocal, P.B., Science 1995, v. 270,
p. 53-59). To take the influence of impacts on recent biological evolution
from speculation based on rather wooly statistics to being worthy of serious
consideration needs several developments:

Detection of "spikes" in the ocean-floor and ice-core records that cannot be
explained by a blend of the Milankovich model with oceanographic and
armospheric factors, or by volcanicity. The best time series for that would
be those bearing on dust and acid rain from electrical conductivity in ice
cores, and carbon isotopes in ocean-floor cores that link to biological
productivity.

Examination of the full terrestrial fossil record of other animals over the
last 5 Ma to seek otherwise inexplicable speciation events and minor,
general extinctions.

It is not a case of the "jury being out", but of the evidence not being in -
it is meagre in the extreme.

Steve Drury
Dept of Earth Sciences
The Open University

============
(11) 90 PERCENT OF WHAT? AND SOME OTHER COMMENTS

From Duncan Steel <D.I.Steel@salford.ac.uk>

Dear Benny,

The following text from an Associated Press item (quoted in CCNet on 2001
April 18) underscores the problem we have in making clear to the media/other
people just what can, and cannot, be done in searches for NEOs.

>How serious the potential threat could be is underscored by an effort
>sponsored by the National Aeronautics and Space Administration to catalog 90
>percent of all near-Earth objects, or NEOs, that are 0.6 miles or larger in
>diameter.

>The objects are a mix of comets - frozen balls of ice and dust that formed
>in the far reaches of the solar system - and asteroids, which were formed in
>the inner solar system between the orbits of Mars and Jupiter.

>Occasionally, those objects are pushed closer to the sun through collisions
>or by the tug of gravity and cross the orbit of the Earth.

>So far, the search effort has turned up about half of an estimated
>population of 1,100 NEOs.

Whilst I am of the opinion that some significant fraction of objects on
cis-jovian orbits are extinct or moribund comets that therefore present
asteroidal appearances, it is clear that "frozen balls of ice and dust" are
not the norm in this population. They are mostly inert rocky and metallic
bodies that will never show any cometary activity again (if any specific
object ever did, as is the case of 4015 Wilson-Harrington, say).

The target of discovery then (that is, the NASA Spaceguard target) is 90
percent of the 1 km (0.6 mile) plus objects of asteroidal appearance in
cis-jovian (short-period) orbits that approach that of the Earth.

That target excludes the "frozen balls of ice and dust" (i.e. comets), and
quite correctly at this juncture. So far as I am aware the majority of very
large objects on Earth-crossing orbits observed over the history of
astronomical research have been comets, mostly in near-parabolic orbits.
Finding 90 percent of those is not feasible, because they spend most of
their time near aphelion, making it possible to find them only as they enter
the planetary region. Readers might care to note that are around 100 million
1 km plus comets per square degree of sky (almost all out in the Oort-Opik
cloud and of no concern to us). That is, at any instant the Moon is hiding
about 20 million comets - if we had the ability to detect such faint objects
in some way. Back in 1976 Mark Bailey suggested in a letter in Nature such
comets could be monitored by watching for they way in which *they* obscure
background stars.

The immediate aim, then, is to find 90 percent plus of the large asteroids
in short-period orbits. These comprise the majority of the impact hazard,
they are the easiest objects to find (barring the small number of active
comets that are simple to spot), and they are the objects we could do
something about if one were found on an Earth-intercept course. We do not at
present have the technology (in particular the propulsion technology)
required to intercept a near-parabolic comet even if found several years
ahead of a terrestrial impact, and in any case cometary impacts are not
predictable in the same way as is possible for asteroids (which are subject
only to gravitational forces). Once we get to the 90 percent level for this
initial target, then we can worry about the 10 percent risk level posed by
near-parabolic comets, or whether we should instead be aiming for 500 metre,
250 metre or 50 metre asteroids.

Re: NASA TO TRACK MORE ASTEROIDS WITH NEW NEAT CAMERA

>Asteroid search efforts got a boost from a new, improved camera installed
>this week for NASA's Near Earth Asteroid Tracking system on the 1.2-meter
>(48-inch) Oschin telescope at the Palomar Observatory near San Diego, Calif.

Congratulations to the NEAT team on this major step forward. All interested
in NEOs will be looking forward to the discoveries that will doubtless stem
from the deployment of this camera on the Oschin Schmidt at Palomar.

Much has been heard of late about the intention of the UK to enter the field
of NEO search and tracking, and the need for southern hemisphere coverage. I
simply note here that the UK Schmidt Telescope (UKST), located at Siding
Spring Observatory in Australia, is of an essentially identical size and
design to the Oschin instrument. There is a difference, though. The UKST is
25 years younger.

Regarding the item about Lake Pingualuk in Quebec (CCNet 2001 April 18):

>Lake Pingualuk is the province's deepest lake and one of the planet's
>youngest and best-preserved craters.

>"It's the second-most-transparent lake in the world," said Raymonde
>Pomerleau of Quebec's Wildlife and Parks Department.

If this is the case then there is the potential here for one field of
astronomy (impact studies) to help another (cosmic ray studies). Neutrino
detectors come in a variety of types: some use the chlorine in dry-cleaning
fluid (e.g. the long-term Princeton experiment at Homestake Mine in South
Dakota), others use heavy water (e.g. the multi-billion dollar heavy water
detector down a mine at Sudbury, Ontario). However, large vats of ordinary
water have also been used (with photomultipliers used to look for flashes
from solar neutrino interactions), and it has been proposed that large
natural bodies of water might be employed. One major problem is water
clarity. If Lake Pingualuk is indeed highly transparent then it sounds like
a good candidate. And if frozen over for much of the year it must be dark
down there.

Duncan Steel

=============
* ABSTRACTS *
=============

(12) BIOGEOGRAPHIC AND CLIMATIC BASIS FOR A NARRATIVE OF EARLY HOMINID
EVOLUTION

BROMAGE TG, SCHRENK F, JOURNAL OF HUMAN EVOLUTION 28: (1) 109-114 JAN 1995

We provide the basis for a scenario of hominid evolution that complies with
both the Habitat Theory of Vrba (1992) and early hominid biogeography. It
expresses the association between faunal turnover and climate change with
significant developments during human evolution (cf. Howell, 1959). This
scenario suggests a single origin for the Parathropus lineage but separate
origins for Homo rudolfensis and Homo habilis from Australopithecus
afarensis and Australopithecus africanus ancestors respectively. The
scenario we propose is bold and as yet unsubstantiated by analyses of
character states and polarities. We hope that this flagrancy will incite
focused research on its assumptions and result in new hypotheses based on a
more holistic accounting of morphology, biogeography, and ecology.

Addresses:
BROMAGE TG, CUNY HUNTER COLL, DEPT ANTHROPOL, 695 PK AVE, NEW YORK, NY
10021.
HESS LANDESMUSEUM, DEPT PALEONTOL, D-64283 DARMSTADT, GERMANY.

Copyright 2001 Institute for Scientific Information

=========
(13) PUNCTUATED EQUILIBRIUM: HUMAN EVOLUTION & NATURAL CATASTROPHES

Ambrose SH: Late Pleistocene human population bottlenecks, volcanic winter,
and differentiation of modern humans JOURNAL OF HUMAN EVOLUTION  34: (6)
623-651 JUN 1998

The "Weak Garden of Eden" model for the origin and dispersal of modern
humans (Harpending et al., 1993) posits that modern humans spread into
separate regions from a restricted source, around 100 ka (thousand years
ago), then passed through population bottlenecks. Around 50 ka, dramatic
growth occurred within dispersed populations that were genetically isolated
from each other. Population growth began earliest in Africa and later in
Eurasia and is hypothesized to have been caused by the invention and spread
of a more efficient Later Stone Age/Upper Paleolithic technology, which
developed in equatorial Africa. Climatic and geological evidence suggest an
alternative hypothesis for Late Pleistocene population bottlenecks and
releases. The last glacial period was preceded by one thousand years of the
coldest temperatures of the Later Pleistocene (similar to 71-70 ka),
apparently caused by the eruption of Toba, Sumatra. Toba was the largest
known explosive eruption of the Quaternary. Toba's volcanic winter could
have decimated most modern human populations, especially outside of isolated
tropical refugia. Release from the bottleneck could have occurred either at
the end of this hypercold phase, or 10,000 years later, at the transition
from cold oxygen isotope stage 4 to warmer stage 3. The largest populations
surviving through the bottleneck should have been found in the largest
tropical refugia, and thus in equatorial Africa. High genetic diversity in
modern Africans may thus reflect a less severe bottleneck rather than
earlier population growth. Volcanic winter may have reduced populations to
levels low enough for founder effects, genetic draft and local adaptations
to produce rapid population differentiation. If Toba caused the bottle
necks, then modem human races may have differentiated abruptly, only 70
thousand years ago. (C) 1998 Academic Press Limited.

Addresses:
Ambrose SH, Univ Illinois, Dept Anthropol, 109 Davenport Hall, 607 S Mathews
Ave, Urbana, IL 61801 USA.
Univ Illinois, Dept Anthropol, Urbana, IL 61801 USA.

Copyright 2001 Institute for Scientific Information

===========
(14) DARWINISM, GRADUALISM AND UNIFORMITARIANISM

Reif WE: Darwinism, Gradualism and Uniformitarianism
NEUES JAHRBUCH FUR GEOLOGIE UND PALAONTOLOGIE-MONATSHEFTE  (11) 669-680 NOV
2000

Gradualism (as opposed to saltationism) is generally regarded as an
important part of DARWIN's set of evolutionary theories. Within the modern
Synthetic Theory of Evolution gradualism is regarded as an essential core-
element of the theory. The discussion of Punctuated Equilibrium has hinged
upon the question of whether this model is compatible with the Synthetic
theory or not. It is shown here that gradualism is no theory at all, but
rather a derivative of uniformitarianism under the assumption that the laws
of genetics, developmental genetics and population genetics held in the
geological past in the same way as today.

Addresses:
Reif WE, Inst & Museum Geol & Palaontol, Sigwartstr 10, D-72076 Tubingen,
Germany.
Inst & Museum Geol & Palaontol, D-72076 Tubingen, Germany.

Copyright 2001 Institute for Scientific Information

=============
(15) NONLINEAR RESPONSE OF BIOTIC SYSTEMS TO COSMIC IMPACTS

Plotnick RE, Sepkoski JJ: A multiplicative multifractal model for
originations and extinctions
PALEOBIOLOGY 27: (1) 126-139 WIN 2001

Recent works have suggested that the fossil record exhibits a fractal
structure; i.e., that processes, such as extinction, follow a power-law size
distribution and their time series show a lif power spectrum. This structure
has been used as evidence that evolutionary dynamics are an example of a
self-organized critical (SOC) process. We have reexamined this claim by
analyzing a detailed record of marine genus-level extinctions and
originations. Our results indicate that neither extinctions nor origination
metrics show the power-law size distribution or a 1/f power spectrum
characteristic of SQC and related models. We also believe that the
underlying assumptions of SOC are incompatible with our understanding of the
processes controlling macroevolutionary patterns. Statistical analyses of
the data sets are compatible, however, with the presence of multifractal
self-similarity in both records, consistent with a hierarchical and
multiplicative generating process. This model assumes that multiple causal
mechanisms, acting over many spatial and temporal scales, interact to
promote or inhibit originations and extinctions. In this view, the same
event can have quite different impacts depending on the state of the biotic
or physical system at the time that it occurs. This may at least partially
explain such phenomena as the imperfect correlation between eustatic
sea-level changes and macroevolutionary processes and the apparent nonlinear
response of biotic systems to bolide impacts.

Addresses:
Plotnick RE, Univ Illinois, Dept Earth & Environm Sci, 845 W Taylor St,
Chicago, IL 60607 USA.
Univ Illinois, Dept Earth & Environm Sci, Chicago, IL 60607 USA.

Copyright 2001 Institute for Scientific Information

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