PLEASE NOTE:
*
CCNet 65/2001 - 9 May 2001
--------------------------
"We are now working on an experimental project on how to get
more
public support for NEO activities. During our NEO observations,
there are
many moving objects (asteroids) in our wide field images. If we
can prepare
and distribute good software to detect these moving objects and
several
wide field images, interested people, who receive them, can
detect a
number of these objects. Last winter, we asked interested
amateurs who would
work on this project with the help of Yomiuri Newspaper Company
and
received a number of applicants. It became a contest how many
asteroids
they could detect. This was carried out using their computers,
and 133
teams reported. They now understand how astronomers detect moving
objects. We find that this is a very effective way to highten
public
interest and support for NEO activities. The Japan Spaceguard
Association
intends to expand this project now to an international level with
the help
of the British Council (Tokyo office).
--Syuzo Isobe, Japan Spaceguard Association, 8 May 2001
"To the conservation biologist, there is little positive to
be said
about extinction. From an evolutionary perspective, however,
extinction is
a double-edged sword. By definition, extinction terminates
lineages and
thus removes unique genetic variation and adaptations. But over
geological
time scales, it can reshape the evolutionary landscape in more
creative
ways, via the differential survivorship of lineages and the
evolutionary
opportunities afforded by the demise of dominant groups and the
postextinction sorting of survivors. The interplay between the
destructive and generative aspects of extinction, and the very
different
time scales over which they appear to operate, remains a crucial
but poorly
understood component of the evolutionary process."
-- David Jablonski, Proc. Natl. Acad. Sci. USA, May 8, 2001
(1) THE RECOVERY OF ASTEROID 1998 KM3
Spaceguard Central Node, 8 May 2001
(2) ADDITIONAL REMARKS ON THE 1998 KM3 RECOVERY
Brian G. Marsden <brian@cfaps5.harvard.edu>
(3) JAPAN SPACEGUARD ASSOCIATION AWARD FOR NEO OBSERVER
Syuzo Isobe <isobesz@cc.nao.ac.jp>
(4) SPACECRAFT MEASURES ASTEROIDAL MAGNETIC FIELD
Harvey Leifert <hleifert@agu.org>
(5) SCIENTISTS WORRY OVER ASTEROIDS (AGAIN)
Daniel Spires <DSpires@wcom.net>
(6) LUNAR NON-IMPACT
Michael Paine <mpaine@tpgi.com.au>
(7) THE CCNet THINK TANK
Andy Smith <astrosafe@yahoo.com>
(8) LESSONS FROM THE PAST: EVOLUTIONARY IMPACTS OF MASS
EXTINCTIONS
Proceedings of the National Academy of
Sciences of the USA, 8 May 2001
(9) AND FINALLY: GENETICALLY MODIFIED EARTH PLANTS WILL GLOW FROM
MARS
SpaceDaily, 8 May 2001
=============
(1) THE RECOVERY OF ASTEROID 1998 KM3
From Spaceguard Central Node, 8 May 2001
http://spaceguard.ias.rm.cnr.it/SSystem/NEOCS/1998km3.html
1998 KM3
The identification of 1998 KM3, which was announced on MPEC
2001-J05 by the
Minor Planet Center, is the result of a successful international
collaboration among different Institutions.
The recovery of this lost PHA is very important for two reasons:
According to recent results by Milani (April 2001, Risk Page of
NEODyS ),
1998 KM3 had some remote probabilities to impact the Earth within
the
current century. Several virtual impactors were identified using
the 1998
data. Also, being about 400 meters in size this was a serious
case.
This case is a demonstration of the potential offered by an
international
coordinated effort when there is the need to deal with very
difficult
recoveries.
Before going into some of the details, let's look back at the
original
message announcing this observing campaign.
The following informative message was posted on the New
Announcement list of
the SCN and sent to the Minor Planet Mailing List on November 24,
2000.
On behalf of the Spaceguard Central Node, we want to draw your
attention on a very interesting PHA, 1998 KM3, which was
recommended by
Andrea Milani. According to his calculations, 1998 KM3 has the
potential to approach the Earth as close as two Earth radii in
the
course of a close encounter in 2083. No collision solutions have
been
detected so far.
There is one problem: 1998 KM3 is virtually lost.
Even though a targeted search would not be impossible in
principle,
given the means available to NEO community, we don't think it is
worth to ask for investing a huge amount of efforts, at least at
this
stage.
According to the present orbital knowledge, there might be a
close
encounter with the Earth in early December 2000, followed by
favourable observing conditions for the rest of month and
eventually part
of January 2001. It is very likely that 1998 KM3 will be
accidentally
rediscovered by the big NEO survey programs sometime in December.
Magnitude
peak of the apparition ranges from about 12.5 - 13 V to about
19.5 -
20.0 V. It is obvious that it might escape detection if it is on
the
"wrong side" of the apparition, but this case serves as
a good test for
the survey programs. We hope that data on newly FMOs could be
made
available to the community as soon as possible.
If, indeed, it will pass unobserved by the end of December,
follow-up actions might be considered using the
"negative" information.
Thank you for your attention and good luck!
Some highlights about this identification
This big challenge of this case is that 1998 KM3 was lost. As
soon as this
announcement was made, we produced 200 possible orbits for 1998
KM3 using
the multiple-solution method with the Orbfit software. The
coverage of the
confidence region was stopped at the 5-sigma level. Near the time
of the
close approach the sky uncertainty was of the order of 100
degrees!
The situation became difficult from the start: after the close
encounter
early in December and the following dark moon period at the end
of the
month, 1998 KM3 had still to be found. To make sure that KM3 did
not escape
detection, we operated in two ways: a) To check all NEO
candidates on the
NEO Confirmation Page whose angular rates/positions could be
compatible with
this object. b) To use the MPC service called MPChecker in order
to cover
all the sky regions at appropriate dates in which the target
could have not
been discriminated from MBOs. All the new objects/designations at
appropriate positions were checked for rates similar to those
expected for
1998 KM3.
Neither of the two checks was successful.
We then concluded that 1998 KM3 was probably not on the side of
the close
encouter, but on the other side of the confidence region.
However, the
object would have been significantly fainter on this side, no
detectable or
marginally detectable by surveys like LINEAR, LONEOS or NEAT.
With these results, the following month we asked Robert McMillan,
PI of the
Spacewatch project, if he could arrange some sky coverage of the
faint side
of the confidence region. Not only he agreed, but, later on, he
was willing
to extend the search further respect to our initial request. A
detailed plan
was put into action, taking advantage of the fact that the sky
uncertainty
was about the half of that of December while its visual magnitude
was still
within the capabilities of Spacewatch.
The coverage of the confidence region was made by J. Montani on
January 19,
by A. Gleason on Jan. 20 and 21, by R. McMillan on Jan. 22 and by
J. Larsen
on Jan. 25 and 26. J. Scotti provided some preliminary blinking
of all the
Spacewatch regions (many degrees long up to the 21.0-21.5
magnitude). The
result of this effort was to cover from -0.5 to + 4.7 sigma, but,
to our
surprise, no candidates for 1998 KM3 were found. To secure the
value of such
an effort, hand blink of all the regions was provided by Arianna
Gleason
around mid-March confirming the negative results.
The negative results of Spacewatch were crucial to conclude that
in fact
1998 KM3 could only be on the side of the close enounter and that
for some
unknown reason could have been missed.
In the meantime, Andrea Milani and his team at the University of
Pisa
upgraded their software and extended the monitoring for possible
collisions
beyond the year 2050. Results of this work were recently posted
on the Risk
Page of NEODyS by Milani: unfortunately the hazard posed by 1998
KM3 was
more serious than previosuly expected. Several collisions were
found; two of
them, in 2071 and 2076, were particularly relevant with
probabilities above
one in a million.
Given the new situation, two plans could be set-up:
a) Re-analyze the work done by the big surveys and study what
margin
of success existed.
b) Organize a last-minute campaign for virtual impactors, in a
similar fashion to the plan made for 1998 OX4.
We started with plan (a): a more detailed analysis was made of
the sky
coverage plots from LINEAR and LONEOS in December using the
asteroid
services site at Lowell Observatory. This allowed to flag several
opportunities for each orbital solution not covered by Spacewatch
(using the
initial sample of 200 orbits). After noticing that every orbital
solution
had been covered at least on one night, we sent two separate
messages to G.
Stokes for LINEAR and T. Bowell for LONEOS, explaining that 1998
KM3 should
have been on one or more of their images/data. We indicated a few
specific
nights and asked them how to retrieve such information.
G. Stokes replied immediately to our message and contacted Brian
Marsden at
the MPC since there was a reasonable chance that 1998 KM3 could
be hidden
among unchecked data in MPC archives. In fact, 1998 KM3 was
identified using
data from this resource on three different nights among the data
of LINEAR.
We also received a very positive answer from T. Bowell and B.
Koehn
regarding the LONEOS data: it turned out that the real orbital
solution was
not covered by LONEOS.
Apparently, LINEAR missed 1998 KM3 on December 5, during the
close
encounter, probably because it didn't image the right region at
the right
time: 1998 KM3 was in fact moving very fast on that night.
As a final remark we would like to add that the key to the
success of this
campaign has been the large effort made by the Spacewatch team
who made a
targeted search over a very large region of the sky.
Andrea Boattini, Germano D'Abramo, The Spaceguard Central Node,
May 8, 2001,
Rome, Italy
==============
(2) ADDITIONAL REMARKS ON THE 1998 KM3 RECOVERY
From Brian G. Marsden <brian@cfaps5.harvard.edu>
It was a pleasure to read the account by Andrea Boattini of the
successful collaboration on the 1998 KM3 recovery. In contrast,
to read
elsewhere in the internet of statements that the Minor Planet
Center was
somehow to "blame" for the time wasted by Spacewatch in
unsuccessfully
searching for the object a month after it was
"recovered" shows that some
colleagues have
a rather imperfect knowledge of how astrometric observations from
NEO
surveys are treated. Because there is no facility at most
of the surveys to
link together the observations of what appear to be main-belt
objects (and a
typical night's imaging will produce some 200 times as many of
these as it
does of candidate NEOs), this linkage is done on their behalf by
the Minor
Planet Center. Sure, the MPC also does a fair bit of work on
unusual objects
like NEOs and TNOs, but the bulk of its work is on MBOs, because
the bulk of
the images are of MBOs. Given that there may be 30,000 or more
observations
on a single night, this night-to-night linkage can be an almost
intractable
problem, given that many days may elapse between the separate
nights of
observations of the same field. The Spaceguard Central Node,
which has about
the same number of employees as the Minor Planet Center, is
designed
specifically to work on NEOs. Since it therefore has 200 times
fewer objects
to work with, and it in fact needs to work only with objects for
which the
initial information has already been correlated and provided by
the MPC, it
can therefore afford to scrutinize the situation with regard to
each NEO
very carefully. The SCN has indeed been doing this work
admirably, in
particular by finding numerous precovery observations on old
photographs
that therefore allow dramatic improvement of the NEO orbit
solutions. In
turn, these new solutions will almost invariably allow the
complete removal
of the candidate impact computations from the Risk Page of the
NEODys,
another organization that can afford to concentrate only on NEOs
and that
often acts in concert with the SCN.
Andrea Boattini notes that he asked
Spacewatch in January to make a
specific search for 1998 KM3 _after_ he had checked that the
object had
shown up, neither on the NEO Confirmation Page nor among the 5000
or so new
multiple-night objects designated by the MPC in December. Indeed,
he
confirmed that 1998 KM3 was not there, a conclusion that had
previously been
quite evident to the MPC. It is in fact a pity that he then felt
that his
principal need was to contact Spacewatch, because it is indeed a
shame that
Spacewatch was then obliged to make the search. If he were eager
to have
1998 KM3 recovered, January was the time when he should instead
have
computed the 200 variant orbits he discusses, at which point he
could have
informed the MPC of the nights when the search programs were
likely to have
recorded the object. The MPC did not in fact receive this
information until
May 3, and the MPC received it then only because that was also
the day
Andrea gave it to Grant Stokes, who immediately passed it on to
the MPC as
the organization entrusted to make the night-to-night linkages.
Specifically, Andrea suggested that LINEAR might have the object
on 2000
Dec. 21 and Dec. 30. This information from Andrea was indeed very
helpful to
me, because it then took me only a matter of minutes to notice
that there
was an object with large but roughly comparable departures from
the 1998 KM3
orbit on these two nights. It took only a minute or two more for
me
unequivocally to verify the two-night identification by linking
these 2000
observations to those in 1998. At the same time, I could also
identify
further LINEAR observations on 2001 Jan. 3, a night that had not
been
mentioned by Andrea but that had already shown up as a
single-night
detection (although the correct object was not clear) in my own
initial
calculations. After checking back with Grant, who immediately
then responded
to Andrea, I published all the recent observations and my new
orbit
computation on MPEC 2001-J05. A fine collaboration indeed, and
the only pity
is that it was initiated on May 3, rather than in, say,
mid-January. 1998
KM3 was not "recovered" in December: it was recovered
on May 3. I also
verified that the 0.021-AU approach to the earth on 2000 Dec. 3
was by far
the closest to occur during the 80 years after the object's
discovery: there
was no possible earth impact.
Why did the MPC not realize previously
that there were multiple nights
of the same object? The nine-day separation between the
pair of nights
noted by Andrea is really too long to do this in any sure way.
The four-day
separation between the second and third nights ought to have been
a better
choice. The motions of the object on these nights individually
showed that
the object was somewhat unusual, but only in the sense that each
object was
likely to have a basically main-belt orbit with a somewhat high
eccentricity. But in that case the two nights would not link
together, for
to do that one would have to know that the object had its
perihelion inside
the earth's orbit, and such objects are rare, even among NEOs.
So, given
that there was a host of other objects around to confuse matters,
it is
really not surprising that this linkage was missed. As for Dec.
21, it is
interesting to see that the motion was perfectly main-belt, even
though the
object was only 0.2 AU from the earth.
No, the only way this recovery would
reasonably have been made is the
way the recovery actually happened. One had to start by carefully
examining
the 1998 KM3 orbit, as Andrea did. With the information
that LINEAR
observations would be likely on the two nights indicated, the
rest was quite
straightforward. I note that much the same happened with 2000
SG344, except
that the essential communications were lost at the time. This
kind of
collaboration between the MPC and the SCN is indeed to be
welcomed, and I
hope it happens still more smoothly in the future.
===============
(3) JAPAN SPACEGUARD ASSOCIATION AWARD FOR NEO OBSERVER
From Syuzo Isobe <isobesz@cc.nao.ac.jp>
Award for an NEO Observer by the Japan Spaceguard Association
As was mentioned by CCNet, the Planetary Society has given awards
for five
NEO observers in 2000. This is a good way to support world-wide
follow-up
teams. The Japan Spaceguard Association started its activities in
1999 as a
non-profit organization registered to the Tokyo Metropolitan City
and also
tried to give an award for an NEO observer. The Association has
received two
applications and its committee chose Mr. Taku Maeno, at the
Mitoko
Observatory in Tokushima prefecture, Japan.
At the annual meeting of the JSGA held on March 31, 2001, Taku
Maeno was
awarded 400,000-yen ($1=\125) for his contributions in NEO
follow-up
observations. The JSGA intends repeat this award activity every
year and
make it expand year by year.
One of effective ways how to get public supports for NEO
activities
The NEO hazard problem is a serious one for human-being. However,
it is not
well understood by the wider public although many active people
on this
problem, including those on CCNet, are making great efforts.
Since NEO
collision probabilities are very low, people do not realize the
inherent
hazard - until it really happens.
The Japan Spaceguard Association is working in different ways to
make the
public realize the general problem. It publishes a journal
regularly and
distributes it to the public. It arranges public lectures several
time per
year. It produces its logo badge and member cards. However, these
efforts
work rather slowly.
We are now working on an experimental project on how to get more
public
support for NEO activities. During our NEO observations, there
are many
moving objects (asteroids) in our wide field images. If we can
prepare and
distribute good software to detect these moving objects and
several wide
field images, interested people, who receive them, can detect a
number of
these objects.
Last winter, we asked interested amateurs who would work on this
project
with the help of Yomiuri Newspaper Company and received a number
of
applicants. It became a contest how many asteroids they could
detect. This
was carried out using their computers, and 133 teams reported.
They now
understand how astronomers detect moving objects. We find that
this is a
very effective way to highten public interest and support for NEO
activities. The Japan Spaceguard Association intends to expand
this project
now to an international level with the help of the British
Council (Tokyo
office).
In the UK, Liverpool John Moores University collaborates with the
JSGA, and
both Japanese and UK schools will become sister schools for this
project,
each of which will represent a team in the contest for moving
objects
detection.
The JSGA hopes readers of CCNet will support these activities.
You can find
related papers at http://neowg.mtk.nao.ac.jp/ase/
==========
(4) SPACECRAFT MEASURES ASTEROIDAL MAGNETIC FIELD
From Harvey Leifert <hleifert@agu.org>
The irregular asteroid Braille (also known as 1992 KD) was
discovered in May
1992. Deep Space 1 (DS1) performed a successful flyby at the
asteroid in
July 1999, passing Braille on the nightside with a relative
velocity of 15
kilometers [nine miles] per second and allowing, for the first
time, a
direct measurement of an asteroidal magnetic field. Richter et
al. ["First
direct magnetic field measurements of an asteroidal magnetic
field: DS1 at
Braille"] conclude that the measured field is simply the
unperturbed dipole
field of the asteroid, and estimate the upper limit of Braille's
magnetic
moment to be about 2.1 X 10^11 ampere meter-squared (A-m^2).
Authors: I. Richter, K.-H. Glassmeier, F. Kuhnke, G. Musmann, C.
Othmer,
Inst. for Geophysics and Meteorology, Technical U. of
Braunschweig,
Braunschweig, Germany; D. E. Brinza, B. T. Tsurutani, JPL,
Caltech,
Pasadena, California; M. Cassel, Inst. for computer and
Communication
Network Engineering, Technical U. of Braunschweig, Braunschweig,
Germany; K.
Schwingenschuh, Ins. For Space Research, Technical U. of Graz,
Graz,
Austria.
=========
(5) SCIENTISTS WORRY OVER ASTEROIDS (AGAIN)
From Daniel Spires <DSpires@wcom.net>
From Yahoo News, 7 May 2001
http://dailynews.yahoo.com/h/ap/20010506/sc/exp_asteroid_impacts_1.html
By ANDREW BRIDGES, AP Science Writer
LOS ANGELES (AP) - A group of scientists is seeking a
standardized protocol
for dealing with the possibility of an asteroid or comet striking
the Earth,
saying humans can do more than the dinosaurs ever could before a
colossal
impact precipitated their extinction 65 million years ago.
The call comes as interest grows in the swarm of asteroids and
comets that
orbit the sun in the Earth's immediate neighborhood. The concerns
were
sparked in part by several recent false alarms about impending
impacts. "In
some sense, it's something we know we need to worry about, but we
need to
decide at what level we need to worry about it -- and that's a
question for
everybody," said Daniel D. Durda, a research scientist in
the department of
space studies of the Southwest Research Institute in Boulder,
Colo.
In recent weeks, a paper written by Durda and fellow scientists
Clark R.
Chapman and Robert E. Gold has been making the rounds among
experts who
study impact hazards. The goal, they write in the 19-page paper,
is to
encourage discussion of how to replace the "haphazard and
unbalanced" way
the world now addresses any potential impact.
"They are spot-on that this is a problem. They are also
right on time in
terms of this just now being recognized as serious enough a topic
so as to
go to the next step in terms of 'what if,'" said Richard
Binzel, a professor
of planetary science at the Massachusetts Institute of Technology
who
developed a scale to rank the potential danger of an impact.
"We have now
overcome the giggle factor."
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, either 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.
"It is really in the last few years the search effort has
begun to bear
fruit and bear it massively," said Thomas Morgan, discipline
scientist for
NASA's NEO observation program.
If an Earth-bound asteroid or comet were spotted, scientists have
proposed
either attaching a rocket engine to it to nudge it out of the
way, or
smashing it to pieces with an atomic bomb.
But even if a warning about a potential impact comes years or
decades in
advance, the feasibility and expense of such a deterrent is
unknown. If an
attempt to destroy or deflect an NEO should fail, and an object
just a
half-mile in diameter struck the Earth, it would unleash an
amount of energy
equivalent to 10 million times the power of the atomic bomb
dropped on
Hiroshima. The event could do for many humans what a larger
object is widely
believed to have done for the dinosaurs.
"The public has all heard of the extinction of the
dinosaurs, and they
expect something to be done about (any potential impact), so
therefore
something should be done," said Bill Cooke, a NASA
contractor and space
environment expert who has penned his own paper on the subject.
The Federal
Emergency Management Agency, for one, would respond in a way
similar to how
it does now with hurricanes -- or the recent return to Earth of
the Russian
Mir space station.
"If we were dealing with a larger object, like an asteroid
that could have a
much more severe impact on the United States, as we have more
advance
knowledge of where it might hit, we would immediately start
alerting states
that something was coming," said Marc Wolfson, a FEMA
spokesman. For now,
word of a potential threat comes by way of a casual bulletin
posted on the Internet that is invariably redistributed by the
media.
"There's nothing set in stone yet as far as procedures go.
That's what we
want to get people talking about: Who should be notified? Who
shouldn't?
There's no desire to be secretive, but you don't want to cry wolf
too
often," Durda said.
Such a cry has come once in each of the past three years, most
recently in
November when astronomers announced an object known as 2000 SG344
had a
1-in-500 chance of hitting the Earth in 2030.
According to a then-new International Astronomical Union policy,
astronomers
made that announcement within 72 hours of reaching a consensus
that a risk
to the planet existed.
With SG344, however, the alarm was retracted almost immediately
as other
astronomers better calculated the object's orbit. "It was a
very normal
scientific process, but in the public's eye it looked like a
mistake,"
Binzel said. "It's a trade-off between being very open and
honest about what
we have and waiting and waiting until we have every last piece of
data in
hand."
One expert said the flaps, while embarrassing, were an issue of
public
relations, and not science. "These are problems in
communication. They are
not problems in the basics of what we're doing," said David
Morrison,
chairman of the International Astronomical Union's working group
on NEOs.
"The issue is really one of how do we communicate with the
media and the
public."
Copyright 2001, AP
[MODERATOR'S NOTE: I apologise if readers feel a bit bored by
this old
story. In fact, it is *exactly* the same story Associated Press
posted
almost a month ago (15 April). Back then, it was released under
the headline
"Doom's day news protocol wanted: Scientists worry about how
to worry about
asteroids", see:
http://search.newschoice.com/Display.asp?story=d:\index\newsarchives\laxpsd\fpg\20010415\797775_isn15ast.txt&puid=1453
].
In the meantime, an for almost
a year now, calls for effective changes to the flawed procedures
for
publicly announcing an "impact threat" have been
ignored. One thus has to
wonder what all this fuss is about, and why AP re-issued the same
story yet
again? Let me put it this way: is this just another PR exercise,
or is there
really a change of heart among those U.S. colleagues who have so
far been
rather reluctant to revised the IAU protocol? BJP
Same old story also at:
SCIENTISTS URGE KILLER ASTEROID PREVENTION PLAN
From CNN, 8 May 2001
http://www.cnn.com/2001/TECH/space/05/08/asteroid.impacts.ap/index.html
SCIENTISTS CONSIDER PROTOCOL FOR MASSIVE ASTEROID IMPACT
From Nando Times, 7 May 2001
http://www.nandotimes.com/healthscience/story/0,1080,500558856-500798437-504292519-0,00.html
============================
* LETTERS TO THE MODERATOR *
============================
(6) LUNAR NON-IMPACT
From Michael Paine <mpaine@tpgi.com.au>
Dear Benny
The following statement from CCNet 4 May doesn't show a very good
understanding of events randomly distributed in time (if impacts
are indeed
random):
"An impact this size on the Moon is predicted to happen once
every
15 million years or so," Paul Withers told BBC News Online.
"Having one
happen in the past 1,000 years would suggest that the predictions
might
be dangerously incorrect and the Earth might be in more danger
from
colliding space rocks than is currently thought."
In any, case LPL's Crater Calculator
(http://www.lpl.arizona.edu/tekton/crater.html
) gives a predicted impactor
diameter of 850m (assuming a stony asteroid generated the 22km
crater on the
Moon), not the 3km quoted in the article. Therefore the odds of
such an
impact in the last 1000 years are very roughly 1 in 1000
(assuming such
Lunar impacts occur with an average interval of one million years
but are
randomly distributed). Therefore a large crater that young on the
Moon would
be unusual but not surprising.
Nevertheless, the evidence seems to be building up against crater
Giordano
Bruno being linked to the 1178AD account.
regards
Michael Paine
=============
(7) THE CCNet THINK TANK
From Andy Smith <astrosafe@yahoo.com>
Hello Benny and CCNet,
It is just great to be connected to this collective brain and to
be
cooperating with all of you, in meeting the most important
technical
challenge in history. There are so many really outstanding
contributions
coming to the Net. Many thanks to the contributors and the host.
The piece that Ed Grondine sent to the 2 May letter was excellent
and we
want to express our appreciation to Ed for that and to Michael
Paine, Duncan
Steel and all of our regular experts, for the work they share.
U.S. Congressional Natural Hazards Caucus
We want to encourage all to contact this group and ask that they
recognize
and address the asteroid/comet danger. One of our top priority
tasks is to
inform policy-makers of the NEO issues. Most are very poorly
informed...and
that is a big part of the problem.
We also devote some effort to the Congressional Space
Sub-Committee, which
Ed mentioned in his paper. There are still a few members on this
committee
who were there and supported emergency readiness during the 1993
hearing.
Congressman Hall is a good example...a senior member and a strong
supporter.
The National Space Society, Planetary Society, the AIAA and
others are all
working to get support on the hill and we commend them.
Things are improving and we encourage continued efforts to inform
policy-makers, around the world. The U.K. folks did an
outstanding job and
are a great model information effort.
The Super Terrestrial Asteroid Telescope (STAT)
At least one large survey instrument is a must (6 to 8 meter
primary with
30k x 30k, or so, CCD). It would be nice if we had more than one
of these
and a good orbiting survey system. We hope the first STAT will be
sposored
by an international program.
We are encouraging other large survey telescopes (Sloan Digital
Sky Survey,
Canada/France/Hawaii, etc.) to help and we are interested in any
ideas and
contacts that might be useful in this recruiting. Also, we are
seeking more
NASA funding to support the great NEO hunting teams, around the
world, and
the increasing number of private astronomers who are helping.
International Planetary Protection Alliance (IPPA)
We plan an IPPA meeting, at the International Space Development
Conference
(ISDC2001), which will be held here in Albuquerque, later this
month. The
agenda will include a discussion of ways to facilitate world-wide
communication and cooperation, on planetary protection, and ways
to increase
support and funding levels. We welcome your e-mail and personal
participation in this meeting and in our Asteroid/Comet Workshops
(next
para.). If you want to make a submissions, just send us
abstracts.
Asteroid/Comet Workshops (ACW)
We now have ACW efforts planned for the International Space
Development
Conference (ISDC2001)...here, later this month; the Air
Force/AIAA SPACE
2001 Conference...here, in August and the American Civil
Engineering Society
and Robotics 2002 Conference, next March. These workshops are all
aimed at
increasing the level of awareness, in the technical world and in
the public
mind.
Space Shield Web Information
The information content on the Russian Space Shield Web page is
growing and
there are some very interesting summaries from the SPE 2000
Conference. We
appreciate the effort which is going into this and we are also
looking
forward to more detailed interception/deflection plans and
studies, in the
near future.
NEODys
This Italian site is doing a terrific job of presenting NEO
technical detail
and it is a great companion to the MPC NEO sites. Our thanks to
both groups.
The European technical community and Spaceguard are making great
progress
and showing great examples of openness and international
cooperation.
Cheers
Andy Smith
=============
(8) LESSONS FROM THE PAST: EVOLUTIONARY IMPACTS OF MASS
EXTINCTIONS
From the Proceedings of the National Academy of Sciences of the
USA, 8 May
2001
http://www.pnas.org/cgi/content/abstract/98/10/5393
Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 10, 5393-5398, May 8,
2001
Lessons from the past: Evolutionary impacts of mass extinctions
David Jablonski*
Department of Geophysical Sciences, University of Chicago, 5734
South Ellis
Avenue, Chicago, IL 60637
Abstract
Mass extinctions have played many evolutionary roles, involving
differential
survivorship or selectivity of taxa and traits, the disruption or
preservation of evolutionary trends and ecosystem organization,
and the
promotion of taxonomic and morphological diversificationsoften
along
unexpected trajectoriesafter the destruction or marginalization
of
once-dominant clades. The fossil record suggests that
survivorship during
mass extinctions is not strictly random, but it often fails to
coincide with
factors promoting survival during times of low extinction
intensity.
Although of very serious concern, present-day extinctions have
not yet
achieved the intensities seen in the Big Five mass extinctions of
the
geologic past, which each removed 50% of the subset of relatively
abundant
marine invertebrate genera. The best comparisons for predictive
purposes
therefore will involve factors such as differential extinction
intensities
among regions, clades, and functional groups, rules governing
postextinction
biotic interchanges and evolutionary dynamics, and analyses of
the factors
that cause taxa and evolutionary trends to continue unabated, to
suffer
setbacks but resume along the same trajectory, to survive only to
fall into
a marginal role or disappear ("dead clade walking"), or
to undergo a burst
of diversification. These issues need to be addressed in a
spatially
explicit framework, because the fossil record suggests regional
differences
in postextinction diversification dynamics and biotic
interchanges.
Postextinction diversifications lag far behind the initial
taxonomic and
morphological impoverishment and homogenization; they do not
simply reoccupy
vacated adaptive peaks, but explore opportunities as opened and
constrained
by intrinsic biotic factors and the ecological and evolutionary
context of
the radiation.
Introduction
To the conservation biologist, there is little positive to be
said about
extinction. From an evolutionary perspective, however, extinction
is a
double-edged sword. By definition, extinction terminates lineages
and thus
removes unique genetic variation and adaptations. But over
geological time
scales, it can reshape the evolutionary landscape in more
creative ways, via
the differential survivorship of lineages and the evolutionary
opportunities
afforded by the demise of dominant groups and the postextinction
sorting of
survivors. The interplay between the destructive and generative
aspects of
extinction, and the very different time scales over which they
appear to
operate, remains a crucial but poorly understood component of the
evolutionary process.
The fossil record is rich in extinction events at all intensities
and
spatial scales, and thus provides the essential raw material for
an
extremely important research objective: the comparative
calibration of
evolutionary responses, both positive and negative, to
perturbation. Despite
limits on direct comparisons to present-day and future events,
discussed
below, paleontological data afford the opportunity to test the
evolutionary
impact of such factors as the initial state of the system, the
nature,
duration, and magnitude of the perturbation, and postextinction
physical and
biotic conditions. Comparative analysis of the Big Five mass
extinctions (1,
2) is just beginning, as is work on the myriad smallerand
sometimes more
localizedevents manifest in the geologic record, and so this
paper is as
much a research agenda as a review. One approach to the problem
is through
the related issues of extinction selectivity and evolutionary
continuity
across mass extinction events in the geologic past. Recent work
on the
geographic fabric of extinction events and their aftermath
suggests that the
spatial dimension of diversity dynamics also will be an important
component
of a rigorous theory of extinction and its evolutionary
consequences, and so
although data are sparse I will raise some of these issues as
well.
Selectivity and Loss
Mass extinctions would be important evolutionary agents even if
they simply
intensified variations in clade survivorship seen in times of low
extinction
rates. For example, if mass extinctions primarily removed
lineages in
decline or in the early stages of diversification, truncating the
time span
available to those and other clades for the acquisition of
evolutionary
novelties, then they would significantly reinforce the stability
of the
status quo. The fossil record shows, however, that the major
extinction
events of the geologic past have played a larger and more complex
role, by
removing not just marginal players but also dominant incumbents,
owing at
least in part to extinction selectivities that are partly
independent of
those seen under "normal" extinction regimes. For
example, factors such as
local abundance, species richness, and species-level geographic
ranges, all
apparently significant during times of low extinction intensities
(3),
played little role in the survival of marine invertebrate clades
during the
end-Cretaceous (K-T) mass extinction, where the data are most
extensive (2,
4, 5, ), and have been unimportant in at least some of the other
mass
extinction events as well (2, 6). At the same time, broad
geographic
distribution at the clade level, regardless of species-level
ranges,
significantly enhanced survivorship at all of the major
extinction events
(2, 4, 7) (note that this discordance across hierarchical levels
means that
surviving clades need not consist of generalized or opportunistic
species,
contrary to some oversimplifications of these results). These
analyses
suggest that clades or adaptations may be lost not because they
are poorly
adapted to the pre(or post) disturbance settings, but because
they lack the
broad geographic deployment or other traits that favor survival
during the
extinction bottlenecka pattern of "nonconstructive
selectivity" (8) that
yields differential survival among clades without promoting the
long-term
adaptation of the biota (2, 6, 9).
This is not to say that traits favored under low extinction
intensities were
never advantageous during mass extinctions: resting stages in
phytoplankton,
occupation of unperturbed habitats or regions, physiological
tolerances that
happened to match the extinction-driving stresses, and perhaps
particular
ecological strategies, all might play a role in survivorship
(10-12).
Further, the broad correspondence between survivorship during
mass
extinction and long-term clade volatility (variance in standing
diversity,
i.e., net diversification rates rather than per-taxon origination
or
extinction rate) (13-15) suggest that other intrinsic biotic
factors (6)
carry over from low to high extinction-intensity regimes. Little
has been
done to explore this possibility, however, or the alternative
that taxa with
high per-taxon turnover rates have a lower threshold for crossing
into the
mass-extinction selectivity regime.
Given that some clades show consistently severe or mild responses
to
extinction events, which suggests that intrinsic biotic factors
are
important determinants of survivorship, why does the
vulnerability of other
clades appear to vary significantly among extinction events (6,
16)? This
question bears critically on the evolutionary consequences of
extinction
events but has received little attention. Potential explanations
range from
long-term hardening of clades by the removaland failure to
re-evolveextinction-prone constituents, to contrasting forcing
mechanisms in
the different extinction events, to fortuitous trait combinations
evolved
under "background" extinction regimes. Such analyses
also are needed to make
better biological sense out of apparent selectivity against major
clades
(e.g., ammonites, mosasaurs, dinosaurs etc. at the K-T boundary)
when other
selectivities appear indifferent to clade membership [e.g.,
widespread vs.
restricted-range bivalves and other taxa at many extinction
events (2, 4)].
I should note that the terms background and mass extinction
should be used
carefully: major extinction events stand out in geologic time
series as
maxima against a local background of lower rates, but the overall
frequency
distribution of extinction intensities is a highly skewed,
unimodal
continuum (9). Contrasts in selectivity between the major
extinction events
and times of relatively low extinction suggest a threshold effect
(2, 5),
but the position and taxonomic generality of that threshold is
uncertain;
comparative analyses that encompass smaller extinction episodes
such as the
Cenomanian-Turonian and Eocene-Oligocene events would be
valuable.
The likelihood of clade- or ecosystem-specific thresholds for the
onset of
mass-extinction selectivities underscores the complexity
underlying
extinction time series in the fossil record, a point sometimes
lost in the
general focus on a few of the most massive events. The direct
comparability
of the Big Five mass extinctions to present-day biodiversity
losses remains
unclear. Although present-day losses are severe and appear to be
accelerating (17), they have yet to approach the scale of the Big
Five
extinctions of the geologic past. For example, the K-T extinction
removed
50% of the marine bivalve genera globally (4), and 97% of the
photosymbiont-bearing coral species (and 83% of those genera)
(18), and the
sampling biases inherent to the fossil record virtually require
that these
victims were drawn from the more abundant and widespread
components of the
biota (2, 9). Viewed in this light, these are shocking statistics
that
exceed even the most severe estimates for present-day losses,
although
long-term projections eventually can approach such magnitudes.
Further, over
the past 2,000 yr species-poor clades and geographically
restricted species
have been the overwhelming majority of losses (19), corresponding
to an
intense version of the "background extinction" regime
rather than the mass
extinction selectivities of the fossil record.
This is neither to belittle the violence being wrought on today's
biodiversity, nor to imply that the fossil record offers few
insights
regarding the future of evolution in the face of human activities
and other
stresses. It does suggest, however, that the most useful
comparisons must go
beyond absolute extinction intensities to involve such factors
as: relative
extinction intensities among regions, clades and functional
groups;
long-term effects of geographic variation not only in extinction
but also in
postextinction biotic interchanges and evolutionary dynamics;
patterns of
biotic continuity, lag times, and innovation as reflected in
postextinction
evolutionary rates and patterns. Also important, of course, are
the looming
questions of what causes the transition to selectivities seen
under
paleontological mass-extinction regimes, and whether that
threshold can be
avoided in the near future. Still unknown, for example, is
whether that
threshold is simply a function of the spatial scale and intensity
of the
forcing perturbation, of the quality of the perturbation [see,
for example,
the apparently more severe biotic effects of increased
seasonality as
opposed to simple changes in mean annual temperature (20)] or
whether
feedbacks involving, for example, the compounding of
perturbations (21), or
the disruption of biotic interactions or community structures
come into
play.
In principle, threshold effects should be detectable in time
series around
mass extinction events, and this would be especially valuable in
light of
the cumulative extinction processes operating today. The
demonstrable
selectivity of extinctions raises the issue of weakening vs.
hardening of
the biota if unfavorable conditions are imposed over a protracted
interval:
as the most vulnerable taxa such as endemic species are lost,
under what
circumstances will the extinction-resistant residue withstand
further
stresses, and when will they give way to the mass-extinction
regime? A
hardening process may underlie the pulse of extinction near the
onset of
Pleistocene glaciation and the dearth of extinction thereafter
(22) (the
end-Pleistocene megafaunal extinction is probably a different
issue), and we
need a better understanding of exactly what separates such events
from the
major mass extinctions, and to what extent such hardening
processes
undermine linear projections of present-day extinction estimates
to future
losses. We can simply appeal again to the spatial scale,
intensity, or
quality of the perturbation, or to the quality of the
perturbation, but this
leads us back to the uncertain nature of the threshold, whether
it is graded
or a step-function, and its potential variation among taxa,
communities, and
regions.
Spatial Patterns
Most paleontological analyses of mass extinctions have neglected
the spatial
dimension, tending to focus instead either on single
stratigraphic sections
or regions, or on synoptic global databases. Both scales have
been extremely
productive, but the global biota is spatially complex, with
diversity
gradients and hotspots (e.g., refs. 23-26) and concomitant
variation in the
generation and persistence of evolutionary novelties and higher
taxa (27)
[although the relation to species-level evolutionary dynamics is
still
unclear (28, 29)]. Paleontological analyses that contain a
spatial
component, for example regarding regional extinction events at
all scales
(30) or the biogeographic fabric of postextinction evolutionary
patterns,
therefore would be especially valuable with reference to
present-day and
future processes. Biotic interchanges in the paleontological
record, such as
the late Cenozoic responses to the joining of North and South
America after
the final uplift of the Panama Isthmus, or the opening of
transpolar
interchange between Pacific and Atlantic, clearly document
asymmetries in
biotic interchanges that correspond to regional differences in
extinction
intensities (31, 32). These paleontological findings that regions
suffering
greater losses were more heavily invaded is an important
verification and
extension into deep time of observations made in modern
communities (33).
Geographical analyses of mass extinctions and their aftermath,
however, show
that more complex dynamics may sometimes operate. For example,
although K-T
extinction intensities were statistically homogeneous for marine
mollusks on
a global scale (except perhaps for shallow, clear-water tropical
platforms),
the evolutionary and biogeographic response was decidedly
inhomogeneous. Of
the four regions analyzed as time series (34), only the North
American Gulf
and Atlantic Coastal Plain showed a prolific but short-lived
burst of
diversification by several clades [termed "bloom taxa"
(35)] that were
quiescent elsewhere and was significantly more subject to
postextinction
biotic invasions. Although further analyses are desirable,
particularly from
a phylogenetic standpoint, these patterns are likely to be
robust: they hold
whether the bloom taxa are treated as a proportion of the biota
or as raw
species numbers when the K-T bottleneck is taken into account
(34).
Furthermore, neither burst nor excess invasion appears in an
extensive new
analysis of an important fauna in the earliest Tertiary of
northern Europe
(36), which is the region most likely to conform to North America
by reason
of proximity and climatic similarity.
Understanding these paleontological patterns is particularly
pressing in
light of the massive biotic interchanges that are currently being
directly
or indirectly mediated by human activities. Why was North America
subject to
more intense invasion after the K-T event despite its
unexceptional (if
severe) extinction intensities? This response implies a nonlinear
between
extinction and invasion intensities, or perhaps simply a
threshold above
which the relation breaks down. Another possibility is that when
losses
approach paleontological mass-extinction levels (that is, 50% of
the
relatively abundant and widespread genera) or are globally both
severe and
homogeneous, qualitative as well as quantitative losses determine
the
probability of the evolutionary excursions and invasions seen in
North
America: the identity of the victims and not just their numbers
becomes
particularly important. The functional role of taxa lost from
each of the
regional biotas will be difficult to assess rigorously, but
divergent
regional responses to homogeneous extinction intensities provide
a natural
experiment sufficiently rich in potential insights to demand
further
investigation. Lockwood's analyses showing no relation between
abundance and
survivorship in this fauna undermines one of the simplest
hypotheses: that
preferential removal of abundant and thus dominant taxa was
masked by a
strictly taxonomic approach (although a detailed parallel
analysis of other
regions is required for a definitive test, of course).
The evolutionary effects of biotic homogenization may depend in
part on how
it is achieved. Homogenization via elimination of endemics will
leave a
residue of already widespread taxa that may be relatively
resistant to
geographic isolation and rapid diversification, whereas
homogenization via
range expansion may more readily promote the origin and
diversification of
new endemic taxa. Invaders are not drawn randomly from the source
biota,
however (34, 37), and this bias could itself channel subsequent
evolution
into narrower pathways among regions than would otherwise be
expected.
Spatial effects may be important in finer scales as well. For
example, in
North America within-habitat molluscan diversity appears to
recover within a
few million years after the K-T extinction (38), but total
regional
diversity evidently does not reach preextinction levels until
roughly 10
million years after the event (34, 35). Although this result
needs to be
verified elsewhere, and tested more rigorously for sampling
artifacts, it
suggests that beta diversity, the differentiation of local faunas
among
habitats and along environmental gradients, takes longer to
recover than
alpha, i.e., local, diversity.
Continuity and Creativity
Mass extinctions have never entirely reset the evolutionary
clock: even the
huge losses at the end of the Permian, which appear to have
permanently
restructured marine and terrestrial communities, left enough taxa
and
functional groups standing to seed the recovery process without
the origin
of new phyla (39). One key to understanding the past and future
evolutionary
role of extinctions will involve the factors that permit the
persistence of
certain biological trends or patternse.g., net expansion or
contraction of
clades or directional shifts in morphologyin the face of
extensive taxonomic
loss and ecological disruption. Besides extinction, at least four
evolutionary patterns can be seen in the fossil record. These
are: (i)
unbroken continuity, (ii) continuity with setbacks, (iii)
survival without
recovery ("dead clade walking"), and (v) unbridled
diversification.
Unbroken Continuity. Some large-scale patterns withstood one or
more of the
Big Five extinctions with little disruption. These include the
continued
dominance of reefs by rugose and tabulate corals and
stromatoporoid sponges
across the Ordovician-Silurian boundary (40, 41), the escalation
of
morphological responses seen in molluscan shells to increased
predation
intensity across the K-T boundary (42), the prolonged Paleozoic
decline of
trilobites (43), and the onshore-offshore expansions and retreats
of a
number of post-Paleozoic marine orders (44).
Continuity with Setbacks. Other trends suffer setbackspresumably
owing to
the contrast between mass extinction and "normal"
selectivitiesbut then
resume their long-term trajectories. These include rising
cheilostome
bryozoan dominance relative to cyclostomes (45), the ecological
expansion of
angiosperms (46, 47) although this may be more an ecological than
an
evolutionary setback, and the spread to greater burrowing depths
by veneroid
bivalves, all at the K-T boundary, the early Paleozoic spread of
suspension-feeding bivalves to offshore shelf environments (48),
and the
overall Paleozoic increase in suture complexity in ammonoids
(49). An
important open question amenable to direct testing and simulation
is whether
such setbacks are generally a simple byproduct of high extinction
intensities (if the extremes of the morphospace volume are
sparsely
occupied, for example, then random extinction could clear those
portions),
or represent selection against the traits being maximized under
low
extinction intensities.
Dead Clade Walking. Clade survival is no guarantee that
preextinction trends
will persist or be reasserted in the postextinction setting. Each
extinction
has examples of clades that survived the extinction event only to
fall into
a marginal role or eventually disappear (dead clade walking).
These include
bellerophontid snails (7) and prolecanitid ammonoids at the
Permo-Triassic
boundary (50), the brachiopod order Spiriferoida after the
end-Triassic
extinction (51), and the planktic foraminiferal Zeauvigerina
lineage after
the K-T event (52). Such lingering demises need to be tested
against
stochastic attrition, of course (43). My preliminary, unpublished
analysis
suggests that the intervals after mass extinctions tend to be
significantly
enriched in taxa that failed to cross the next stage boundary,
relative to
other intervals before the extinction event; in other words more
clades that
survived a mass extinction tend to dwindle or disappear shortly
after the
event than would be expected by chance. Also intriguing is the
geographic
variation in the proportion of dead clade walking taxa across the
K-T
boundary, with values highest not in North America (which makes
an
interesting statement on the impact of the greater influx of
invaders
therethey followed extinctions but did not drive them), but in
the tropical
Indian Ocean.
These diverse postextinction trajectories again demonstrate that
analysis of
the evolutionary role of extinctions must include much more than
taxonomic
survivorship at the event itself. We need to understand why some
clades, and
some polyphyletic trends such as escalation of antipredatory
defenses,
persist uninterrupted across the extinction event, why others
stumble but
recover their preextinction trajectory, and still others survive
but never
recover. All of the patterns discussed so far strongly attest
that
postextinction evolutionary processes involve not simply
unbridled radiation
(see below), but a sorting of survivors in the postextinction
world. At this
early stage, many alternative hypotheses are feasible and the
relative power
of the alternatives may vary among different situations. The most
obvious is
the taxonomic breadth of the trend: all else being equal, any
evolutionary
trend that advances along a broad ecological or taxonomic front
is less
likely to be halted by extinction. Although this is surely a
factor, it is
unlikely to be sufficient in all cases, because many trends are
fairly
circumscribed phylogenetically, as in the bryozoan and veneroid
examples
given above.
Given the discordance in selectivity between times of high and
low
extinction intensities, another factor in the persistence of
trends is
likely to be the strength of association between traits involved
in trends
and those related to survivorship. The role of this
macroevolutionary
linkage in promoting the long-term persistence of trends is
virtually
unexplored. A final potential explanation is even more
context-specific,
that the differential persistence of trends depends less on the
intrinsic
traits of clades than on the strong variation recorded in
postextinction
recovery (i) among ecosystems, e.g., the more rapid recovery of
diversity in
oceanic plankton vs. marine benthos (53, 54) (with potentially
important
implications for the relative persistence of mineral and nutrient
cycles);
(ii) across ecological scales, e.g., discordances in the time to
recovery of
local vs. global diversity (as mentioned above, with potentially
important
implications for the accumulation of biological diversity and the
development of spatial structure); and (iii) among regions in
clade dynamics
and biotic interchanges, e.g., the concentration of bloom taxa
and
postextinction invasions in particular areas (with potentially
important
implications for the persistence and recovery of local biotas and
intrerregional source-sink dynamics).
Unbridled Diversification. The most dramatic and creative
evolutionary role
of mass extinctions is the promotion of postextinction
diversifications,
typified most vividly by the exuberant radiation of the mammals
after the
demise of the dinosaurs and other reptilian clades at or near the
K-T
boundary. Postextinction bursts of diversification have been
extensively
discussed and documented for many extinction events, both
morphologically
and at several taxonomic levels (6, 39, 41, 55-58). Therefore,
before
returning to the need for further analysis of geographic
variation in
evolutionary dynamics, I will make only two further points, on
predictability and time scales.
Predictability. Although the evolutionary response to mass
extinction has
sometimes been depicted simply in terms of the reoccupation of
preextinction
adaptive peaks ("reinventing the ecological wheel,"
ref. 59), evolution is
both too opportunistic and too constrained by inherited body
plans for this
to be wholly true. Striking convergences in form and habit are,
of course, a
major theme in evolution, but postextinction dynamics are
complicated by
near-simultaneous radiation of multiple clades [with the powerful
incumbency
advantage at stake (32)], the distinct ecological context of each
postextinction interval, and the raw material provided by
surviving
lineages. These effects can be seen in the incomplete congruence
of
successive occupations of morphospace after extinction events
(60, 61).
To drive home these important but somewhat abstract points on the
long-term
prospects for evolutionary replacements, consider the Cenozoic
history of
birds. The large, flightless phorusrhacid and diatrymid birds,
probably the
top carnivores of early Cenozoic terrestrial communities (62,
63),
interfered with the triumphant mammalian ascent to center stage
in the
postdinosaurian world, and probably were not replaced by an exact
mammalian
analog once they disappeared. Note also that these carnivorous
birds
opportunistically converged on theropod dinosaurs rather than
adhering to
the pterosaur models that might have been the most likely targets
for
convergence given a flying avian starting point (62). Over the
course of
Cenozoic diversification, other birds did assume modes of life
similar to
those vacated by pterosaurs: skimmers may roughly correspond to
Tropeognathus with its keeled jaws, swallows and swifts to
Pterodactylus
with its similar size and wing proportions, flamingos to
Pterodaustro with
its bristling array of fringe-like teeth, and perhaps even
condors to the
enormous Quetzlcoatlus (64, 65). This does not mean, however,
that birdsor
even birds plus batsmanaged to occupy the full range of pterosaur
habits
(66). Equally important, the granivorous habit so important in
modern birds
evidently represents a novel expansion of bird ecospace relative
to their
supposed pterosaur models (see ref. 66 on the avian trophic
diversification). There may be good functional or ecological
reasons for
this (e.g., was the Mesozoic seed bank as rich and dependable a
resource as
in the angiosperm-dominated Cenozoic?), just as there seems to
have been for
the absence of baleen-like filter-feeding in Mesozoic marine
reptiles (67),
but such constraints and contingencies are precisely the factors
that
prevent a given set of clades at a given time from fully
overlapping the
evolutionary pathways of their predecessors. Attempts to predict
evolutionary behavior after major extinction events can only
operate in
broad generalities, and always with the caveat, "expect the
unexpected."
Time Scales. The fossil record shows that destructive and
generative aspects
of extinction generally operate in different time frames, as many
authors
have pointed out (2, 41, 68). The biotic impoverishment and
homogenization
necessarily precedes the evolutionary response, and there is
surprisingly
little hard evidence for major evolutionary innovations within a
major
extinction episode. Even for apparently protracted or multistep
extinctions
that see origination within the extinction interval, such as the
end-Ordovician or end-Permian episodes, "little biological
innovation is
apparent" (41).
Recoveries of different biomes, clades, or communities may have
different
postextinction lag times; for example, broadly defined
"reef" systems lag
behind oceanic plankton systems (see ref. 2 for discussion).
Whether these
lags reflect a general property of large-scale diversity dynamics
(13, 69),
sampling and other biases (6, 70), the duration or intensity of
environmental stresses (71), a protracted process of assembling
new
ecological communities (2, 72), or evolutionary waiting times set
by
intrinsic diversification rates (73) awaits further comparative
analysis.
Geography. The spatial dimension is important not only to
extinction
selectivity and postextinction interchange, but to long-term
evolutionary
dynamics in a postextinction world. Certain habitats and regions,
such as
onshore marine settings (44), and the tropics in both marine (27)
and
terrestrial (74-76) settings, appear to be important sources of
postextinction evolutionary novelty, but the implications of this
nonrandom
creativity have only begun to be explored. On finer geographic
scales, a
systematic search for diversity hotspots in the geologic record
to test for
their long-term persistence and evolutionary significance would
be valuable.
For example, is the end-Ordovician extinction of brachiopods and
other
benthic taxa in North America a potential case study in the
destruction and
later refurbishment of a diversity hotspot? North America
straddled the
equator and harbored a rich biota of endemic taxa in the
epicontinental sea
that occupied the center of the continent. Oscillating climates
and
fluctuating sea levels virtually eliminated this and other
interior seaways
and their biotas, and the postextinction interval saw an invasion
pulse as
taxa from outside the region expanded to occupy the returning
favorable
habitats (77, 78).
Tracking such hotspots and other crucibles of biotic novelty over
evolutionary time might help to prioritize targets for both
research and
conservation efforts in the near future. Do relatively localized
hotspots
primarily contribute taxonomic richness to the global biotic
inventory, or
are they also important reservoirs of biodisparity, that is
morphological
richness? The evolutionary importance of the answer will depend
in part on
the mean lifetime of such hotspots, and the extent to which
novelties that
arise in hotspots tend to spread elsewhere, as has been
documented for
novelties that originated in onshore environments or within
tropical
latitudes (27, 44, 74-76). For these and many other questions,
paleontology
can be a rich source of natural experiments in macroevolutionary
dynamics
before, during, and after perturbations of widely varying
intensities and
durations.
Conclusion
I would not go far wrong in saying that the most dramatic
evolutionary
effects of mass extinctions can be epitomized in just four words:
they
remove successful incumbents. But going beyond what amounts to a
concession
to contingency, what are the lessons of the past that transcend
the specific
mechanisms, intensities, and participants of earlier events?
(i) Mass extinctions happen. The fossil record provides ample
evidence that
even the more widespread and species-rich clades, ecosystems, and
biogeographic provinces are not infinitely resilient.
Biogeochemical and
other data are accumulating on the concomitant breakdown of
nutrient cycling
and other ecosystem-level processes (53), and the links among the
collapse
and recovery of taxonomic diversity, morphological, or functional
disparity
and ecosystem function should be a high priority.
(ii) Survivorship during mass extinctions need not be closely
related to
many aspects of biological success as measured during
"background" times. An
understanding of the evolutionary role of mass extinctions
requires
continued analysis of why well-established incumbents are lost,
surely at
least in part a function of the spatial scale of perturbations,
and the
long-term consequences of such losses.
(iii) Extinction itself promotes biotic interchange. Asymmetries
in ancient
biotic interchange generally appear to reflect geographic
differences in
extinction intensity. The K-T extinction shows, however, that
although
biotic interchanges pervade the postextinction world, simple
linear
relationships can break down to produce unexpected source-sink
patterns.
(iv) The evolutionary response to mass extinction is slow on
human time
scales, difficult to predict owing to the contingencies of
postextinction
conditions including the identity and evolutionary dynamics of
the
survivors, and geographically heterogeneous. Each of these
complications,
however, is amenable to comparative paleontological analysis and
modeling,
with the attendant opportunities for detecting patterns, testing
hypotheses,
and drawing lessons relevant to the future of evolution.
Acknowledgements
I thank D. H. Erwin, S. M. Kidwell, A. H. Knoll, R. Lockwood, and
D. M. Raup
for valuable discussions and reviews, N. Myers and A. H. Knoll
for the
invitation to participate in such a stimulating interdisciplinary
symposium,
and the National Science Foundation and the John Simon Guggenheim
Memorial
Foundation for support.
Abbreviation
K-T, end-Cretaceous.
* E-mail: djablons@midway.uchicago.edu.
This paper was presented at the National Academy of Sciences
colloquium,
"The Future of Evolution," held March 16-20, 2000, at
the Arnold and Mabel
Beckman Center in Irvine, CA.
Lockwood, R. (1997) Geol. Soc. Am. Abstr. Programs 29, A-404.
Lockwood, R. (1998) Geol. Soc. Am. Abstr. Programs 30, A-286.
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Copyright © 2001 by the National Academy of Sciences
========
(9) AND FINALLY: GENETICALLY MODIFIED EARTH PLANTS WILL GLOW FROM
MARS
From SpaceDaily, 8 May 2001
http://www.spacedaily.com/news/food-01c.html
by Paul Kimpel
Gainesville - May 8, 2001
In what reads like a story from a 1950s science fiction magazine,
a team of
University of Florida scientists has genetically modified a tiny
plant to
send reports back from Mars in a most unworldly way: by emitting
an eerie,
fluorescent glow. If all goes as planned, 10 varieties of the
plant could be
on their way to the Red Planet as part of a $300 million mission
scheduled
for 2007.
The plant experiment, which is funded by $290,000 from NASA's
Human
Exploration and Development in Space program, may be a first step
toward
making Mars habitable for humans, said Rob Ferl, assistant
director of the
Biotechnology Program at UF.
Ferl and a team of molecular biologists chose as their subject
the
Arabidopsis mustard plant. They picked it, Ferl said, because of
three
attributes that make it ideally suited for the Mars mission: Its
maximum
height is 8 inches, its life cycle is only one month and its
entire genome
has been mapped. Moreover, in December 2000 it became the first
plant to
have its genetic sequence completed.
To create the glow, the team will insert "reporter
genes" into varieties of
the plant, which will express themselves by emitting a green glow
under
adverse conditions on Mars. Each reporter gene will react to an
environmental stressor such as drought, disease or temperature.
For example,
one version will glow an incandescent green if it detects an
excess of heavy
metals in the Martian soil; another will turn blue in the
presence of
peroxides.
In fact, one of the reporter genes itself is somewhat
otherwordly, having
come from the depths of the ocean.
"What makes the plants glow blue is a protein derived from
an incandescent
jellyfish whose DNA is spliced into the mustard plant," Ferl
said. "The
implanted DNA then synthesizes the iridescent blue protein in the
plant,
which expresses itself under stress."
Ferl's team, in collaboration with Andrew Schuerger, a manager of
Mars
projects at the Kennedy Space Center-based Dynamac Corp., is
competing with
other biologists to receive the NASA contract for the Mars trip.
But both men, who also are professors at UF's Institute of Food
and
Agricultural Sciences, have worked with NASA before. In 1999,
Ferl sent 40
reporter-gene plants into orbit aboard the space shuttle. On that
flight,
gravity had an adverse effect on the plants' ability to utilize
water, a
condition called "space adaptation syndrome."
The scientists are using that experience to engineer smarter
plants.
"Just like humans, plants must learn how to adapt to a new
environment,"
Ferl said. "We are using genetics to create plants that have
the ability to
give us data we can use to help them survive."
The 2 1/2-year Mars mission -- nine months traveling 286 million
miles each
way and one year stationed on the planet -- would work like this:
The seeds
of the plant would make the trip aboard a spacecraft similar to
NASA's Mars
Odyssey, which was launched April 7.
Upon arrival, the landing vehicle's robot would scoop up a
portion of
Martian soil, and the scientists will analyze it using the robot
and a
specialized camera. After modifying the soil with fertilizers,
buffers and
nutrients, the scientists will germinate the seeds and grow the
plants in a
miniature greenhouse on the landing vehicle.
Despite working with alien soil they know little about, the
biologists are
optimistic about the experiment.
"I'm confident we can grow plants if we know the pH levels
and the oxidizing
agents in the Martian soil," Schuerger said. "We'll
test the soil before
planting, and then we can raise or lower pH, flush excess salts
and add
nutrients as needed."
As for long-term plans, Ferl and Schuerger have worked together
on a concept
called "terra-forming" or "ecosynthesis,"
which would use plants to reduce
the carbon dioxide in the Martian atmosphere and produce oxygen
for life
processes. Although the plants are genetically engineered to
detect -- and
then adapt to -- certain environmental stressors, terra- forming
presents
additional obstacles.
Schuerger said that on Mars, daily temperatures range from a high
of 45
degrees Fahrenheit at noon to a low of minus 170 degrees at
night. Also, the
planet's moisture content is 0.3 percent, which is extremely low.
But Ferl, Schuerger and the rest of the team are taking all
bettors.
"I have no doubt that we can get plants to survive on
Mars," Ferl said.
"When we do, we will have shown that Earth-evolved life is
capable of
thriving in distant worlds, and we will have set the stage for
human
colonization."
Copyright 2001, SpaceDaily
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