MARSBUGS:  The Electronic Exobiology Newsletter 
Volume 3, Number 9, 19 August, 1996.

Editors:

David Thomas, Department of Biological Sciences, University of 
Idaho, Moscow, ID, 83844-3051, USA, thoma457@uidaho.edu.

Julian Hiscox, Microbiology Department, BBRB 17, Room 361, 
University of Alabama at Birmingham, Birmingham, AL 35294-2170, 
USA, Julian_hiscox@micro.microbio.uab.edu.

MARSBUGS is published on a weekly to quarterly basis as warranted 
by the number of articles and announcements.  Copyright of this 
compilation exists with the editors, except for specific 
articles, in which instance copyright exists with the 
author/authors.  E-mail subscriptions are free, and may be 
obtained by contacting either of the editors.  Contributions are 
welcome, and should be submitted to either of the two editors.  
Contributions should include a short biographical statement about 
the author(s) along with the author(s)' correspondence address.  
Subscribers are advised to make appropriate inquiries before 
joining societies, ordering goods etc.  Back issues may be 
obtained via anonymous FTP at:  ftp.uidaho.edu/pub/mmbb/marsbugs.

The purpose of this newsletter is to provide a channel of 
information for scientists, educators and other persons 
interested in exobiology and related fields.  This newsletter is 
not intended to replace peer-reviewed journals, but to supplement 
them.  We, the editors, envision MARSBUGS as a medium in which 
people can informally present ideas for investigation, questions 
about exobiology, and announcements of upcoming events.  
Exobiology is still a relatively young field, and new ideas may 
come out of the most unexpected places.  Subjects may include,  
but are not limited to:  exobiology proper (life on other  
planets), the search for extraterrestrial intelligence (SETI), 
ecopoeisis/terraformation, Earth from space, planetary biology, 
primordial evolution, space physiology, biological life support  
systems, and human habitation of space and other planets.
-----------------------------------------------------------------

INDEX

1)	REMARKS BY THE PRESIDENT UPON DEPARTURE [regarding possible 
early life on Mars]
	White House Press Release

2)	ON THE ANNOUNCEMENT REGARDING POSSIBLE EARLY LIFE ON MARS
	Neal Lane

3)	THE STARDUST CONNECTION WITH THE MARTIAN METEORITE AND LIFE 
ON MARS
	Leonard David

4)	CITIZEN'S GROUP WARNS AGAINST BUREAUCRATIC RUSH TO MARS
	Press release

5)	MARS METEORITE HOME PAGE
	Ron Baalke

6)	AERONAUTICS AND SPACE REPORT RELEASED
	Roger Launius

7)	CREW NAMED TO FIRST SPACE STATION ASSEMBLY FLIGHT
	NASA release 96-169

8)	SEARCH FOR PAST LIFE ON MARS:  POSSIBLE RELIC BIOGENIC 
ACTIVITY IN MARTIAN METEORITE ALH84001 [Full text of the 
Science article]
	David S. McKay, Everett K. Gibson Jr., Kathie L. Thomas-
Keprta, Hojatollah Vali, Christopher S. Romanek, Simon J. 
Clemett, Xavier D. F. Chillier, Claude R. Maechling, Richard 
N. Zare

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

REMARKS BY THE PRESIDENT UPON DEPARTURE
White House Press Release

August 7, 1996, 1:15 P.M. EDT, The South Lawn.

THE PRESIDENT:  Good afternoon.  I'm glad to be joined by my 
science and technology adviser, Dr. Jack Gibbons, to make a few 
comments about today's announcement by NASA.

This is the product of years of exploration and months of 
intensive study by some of the world's most distinguished 
scientists.  Like all discoveries, this one will and should 
continue to be reviewed, examined and scrutinized.  It must be 
confirmed by other scientists.  But clearly, the fact that 
something of this magnitude is being explored is another 
vindication of America's space program and our continuing support 
for it, even in these tough financial times.  I am determined 
that the American space program will put it's full intellectual 
power and technological prowess behind the search for further 
evidence of life on Mars.

First, I have asked Administrator Goldin to ensure that this 
finding is subject to a methodical process of further peer review 
and validation.  Second, I have asked the Vice President to 
convene at the White House before the end of the year a 
bipartisan space summit on the future of America's space program.  
A significant purpose of this summit will be to discuss how 
America should pursue answers to the scientific questions raised 
by this finding.  Third, we are committed to the aggressive plan 
we have put in place for robotic exploration of Mars.  America's 
next unmanned mission to Mars is scheduled to lift off from the 
Kennedy Space Center in November.  It will be followed by a 
second mission in December.  I should tell you that the first 
mission is scheduled to land on Mars on July the 4th, 1997--
Independence Day.

It is well worth contemplating how we reached this moment of 
discovery.  More than 4 billion years ago this piece of rock was 
formed as a part of the original crust of Mars.  After billions 
of years it broke from the surface and began a 16 million year 
journey through space that would end here on Earth.  It arrived 
in a meteor shower 13,000 years ago.  And in 1984 an American 
scientist on an annual U.S. government mission to search for 
meteors on Antarctica picked it up and took it to be studied.  
Appropriately, it was the first rock to be picked up that year--
rock number 84001.

Today, rock 84001 speaks to us across all those billions of years 
and millions of miles.  It speaks of the possibility of life.  If 
this discovery is confirmed, it will surely be one of the most 
stunning insights into our universe that science has ever 
uncovered.  Its implications are as far-reaching and awe-
inspiring as can be imagined.  Even as it promises answers to 
some of our oldest questions, it poses still others even more 
fundamental.

We will continue to listen closely to what it has to say as we 
continue the search for answers and for knowledge that is as old 
as humanity itself but essential to our people's future.

Thank you.
-----------------------------------------------------------------

ON THE ANNOUNCEMENT REGARDING POSSIBLE EARLY LIFE ON MARS
by Dr. Neal Lane
Director, National Science Foundation

Today's announcement of scientific evidence for possible early 
life on Mars reignites the excitement of discovery and pioneering 
spirit which motivates all science, and reinforces the need to 
continue our national investment in scientific research.

The 4.5-billion-year-old meteorite which offers this 
unprecedented potential for new scientific knowledge was found in 
Antarctica during an ongoing National Science Foundation research 
project.  It is ironic that we found signposts to possible life 
outside of earth by searching in the most remote location on 
earth.  Antarctica is `the mother lode' of meteorites, and has 
yielded more than 16,000 meteorites so far--close to one-half of 
the world's scientific samples.  The annual hunt for Antarctic 
meteorites is like a bargain-priced space mission that lets 
scientists explore extraterrestrial worlds without leaving their 
home planet.  Occasionally one of the samples evolves into a 
treasure of new knowledge that reveals itself slowly and 
gradually, through scientific scrutiny.  In the case of the 
meteorite discussed today, it was only by using the most recent 
and advanced scientific equipment that researchers were able to 
begin to unlock its mysteries.  The NSF-funded science team which 
discovered the meteorite--led by researchers Bill Cassidy and 
John Schutt of the University of Pittsburgh--were not even 
focused on the implications of organic life on other planets when 
they plucked the now-famous space rock from the frozen continent 
in 1984.

In spite of the many impressive scientific advances that seem to 
occur at an ever faster pace, there is still so much we don't 
know about our universe and the life it holds.  The results 
announced today are not definitive, as the research team itself 
points out.  Rigorous science will continue to unfold the nature 
and origins of life, whether on earth or elsewhere in the 
universe.

We live in a golden age of science, which we hope will continue 
to unlock the secrets of the unknown for the benefit of all 
humankind.
-----------------------------------------------------------------

THE STARDUST CONNECTION WITH THE MARTIAN METEORITE AND LIFE ON 
MARS
by Leonard David

What do martian meteorites and the possibility of life on Mars 
have to do with the STARDUST mission to a comet?  Quite a bit 
actually.

Scientists have speculated for more than three decades now that 
the rich abundance of organic compounds found naturally in comets 
may be related to the origin of life.  As comets impact planets, 
they deliver elements and molecules from which the first living 
organism could have developed.  For this reason alone, the new 
information that STARDUST will provide is vital to planetary 
exploration.  Furthermore, the organic materials (the PAHs) 
trapped in the martian meteorite mineral grains need to be 
compared with organic material from comets to determine whether 
they are biomarkers of life rather than simply organic 
contamination from natural sources.

STARDUST, being NASA's first automated sample return mission, 
will blaze the trail for future Mars sample returns since its 
capsule enters the Earth's atmosphere at a velocity equivalent to 
that of a capsule returning from Mars.  STARDUST is already 
developing technology which can be applied to bringing back 
samples from Mars--missions which are now at extremely high 
priority for exploring the possibility of past life on the red 
planet.

Finally, the intriguing results obtained with martian meteorites 
is just further evidence of the value of having samples back in 
laboratories on Earth.  Although important new data can and will 
be obtained from instruments carried into space, such as 
STARDUST's planned camera pictures of the cometary nucleus, there 
is no substitute for the power of sophisticated instruments and 
advanced laboratory micro-analytical techniques that only sample 
return missions can make possible.

* Note:  The STARDUST mission is part of NASA's Discovery 
Program.  It is slated for launch in 1999 and will encounter 
Comet Wild-2 in 2004, returning to Earth samples of inter- 
stellar dust particles and cometary material in 2006.

Check out the new STARDUST web:
http://stardust.jpl.nasa.gov/

Catherine Collins is the STARDUST Opportunity Director at the Jet 
Propulsion Laboratory.
E-Mail:  Catherine.H.Collins@jpl.nasa.gov  
Phone:  818-354-3257.
-----------------------------------------------------------------

CITIZEN'S GROUP WARNS AGAINST BUREAUCRATIC RUSH TO MARS
Press release [7 August, 1996]

The Space Frontier Foundation, a national grass roots space 
policy and media organization, today warned against any effort to 
create a massive international program to explore Mars.  Citing 
the huge costs and almost decade long delays caused by a similar 
approach to building the International Space Station, the 
Foundation called for the President to order NASA try new, 
innovative and much lower cost methods in the quest for knowledge 
about the possibility of life on Mars.  For example, as a first 
step, the organization wants the US to offer to buy Martian soil 
samples from US firms, saving taxpayers billions of dollars, 
while encouraging a now struggling domestic space industry.

According to Rick N. Tumlinson, President of the Foundation, 
"NASA's traditional plans to return a sample of Mars soil would 
cost around $8 billion; a far better way would be for the space 
agency to procure soil samples from private firms, which are 
better equipped to mount low cost missions than the government. 
We believe this would cost the taxpayers a tenth of the 
traditional government-does-it-all approach."

Today's news of the possibility of life on Mars will inevitably 
lead to calls for sample return missions from the Red planet, to 
provide definitive answers to the questions raised by this 
exciting discovery.  The Foundation believes that the traditional 
NASA bureaucratic style has been discredited, and points to NASA 
Administrator Dan Goldin's own move toward producing cheaper, 
better and faster results by procuring launch services from 
privat= firms, privatizing shuttle operations, and the new X-33 
government-commercial sector partnership.

Tumlinson stated, "We can spend tens of billions of dollars today 
on a series of huge international projects that might someday in 
the future repeat the old Apollo flags and footsteps stunt in the 
red sands of Mars or we can toss out the old way of doing things, 
save billions, get there faster and create a new and vital space 
industry that can provide the infrastructure we need to 
permanently open the space frontier to our children.  It all 
boils down to making the right decisions today."

The Space Frontier Foundation is a grass roots organization of 
American citizens dedicated to opening space to economic 
development and human settlement as soon as possible.  For 
information on the Foundation call 1-800-78SPACE.

57 East 11 Street, 9th Floor, New York City 10003 
Our E-Mail Address is OPENFRONTIER@DELPHI.COM
Web page: http://www.space-frontier.org
-----------------------------------------------------------------

MARS METEORITE HOME PAGE
by Ron Baalke, JPL

I've created a new Mars Meteorite home page now available at the 
following URL:

http://www.jpl.nasa.gov/snc/

The following items are provided on this home page:

*Information is on each of the known Mars meteorites.
*Photos of 11 of the 12 known Mars meteorites.  (If anyone has a 
photo of the Yamato meteorite, let me know!  I'd like to 
complete the set).  Included are photos of Mars meteorites 
from my personal collection.
*Several new photos of ALH 84001 not previously available on the 
Internet.  ALH 84001 is the meteorite causing the recent 
excitement by providing evidence of possible life on Mars.
*The latest news on the discovery of possible life on Mars.
*Links to other related home pages including upcoming missions to 
Mars.
-----------------------------------------------------------------

AERONAUTICS AND SPACE REPORT RELEASED
by Roger Launius, NASA Chief Historian

The NASA History Office has just printed the fiscal year 1995 
AERONAUTICS AND SPACE REPORT OF THE PRESIDENT.  This report 
presents an annual update of the activities of the Federal 
government concerning aeronautics and space activities.  In
addition to a narrative, it also includes extremely useful 
appendices of key documents issues during the year and budget, 
flight, and resources data difficult to find elsewhere.

Anyone who would like a copy can pick them up free of charge in 
the NASA History Office.  We will also send copies through the 
mail, but please send by August 31, 1996, a written request, 
either e-mail or through regular postal channels.  Our postal 
address is:  NASA History Office, Code ZH, NASA Headquarters, 
Washington, DC 20546.  The e-mail address is 
rlaunius@hq.nasa.gov.  Be sure to include a name and postal 
address on the request.  We will prepare a mailing of those 
requesting copies in early September so that we can take 
advantage of bulk mailing rates.
-----------------------------------------------------------------

CREW NAMED TO FIRST SPACE STATION ASSEMBLY FLIGHT
NASA release 96-169

Astronaut Robert D. Cabana (Col., USMC) will command the first 
Space Shuttle mission to carry hardware to space for the assembly 
of the International Space Station in late 1997.  Joining Cabana 
on the flight deck for mission STS-88 aboard Endeavour will be 
pilot Frederick "Rick" Sturckow (Major, USMC), a member of the 
1995 astronaut class who will be making his first space flight. 
Rounding out the crew are veteran mission specialists Nancy 
Currie (Major, USA), Jerry Ross (Col., USAF), and Jim Newman, 
Ph.D.

The seven-day mission will be highlighted by the mating of the 
U.S.-built Node 1 station element to the Functional Energy Block 
(FGB) which will already be in orbit, and two spacewalks to 
connect power and data transmission cables between the Node and 
the FGB.  The FGB, built by Boeing and the Russian Space Agency, 
is scheduled for launch on a Russian Proton rocket from the 
Baikonur Cosmodrome in Kazakstan in November 1997.

"We're pleased to have Bob command this first flight to begin the 
assembly of the International Space Station," said David C. 
Leestma, director of Flight Crew Operations. "This is a talented 
crew facing a very challenging and exciting mission."

Node 1 will be the first Space Station hardware delivered by the 
Space Shuttle.  It has two Pressurized Mating Adapters (PMA), one 
attached to either end.  One PMA is permanently mated to the FGB 
and the other used for orbiter dockings and crew access to the 
station.  Node 1 also will contain an International Standard 
Payload Rack used to support on-orbit activities once activated 
after the fifth Shuttle/Station assembly flight.

"I couldn't be more pleased by the selection of this exceptional 
crew for this mission.  This flight is of critical importance to 
the assembly of the International Space Station.  I have every 
confidence in Colonel Bob Cabana and the STS-88 crew and their 
successful execution of this historic endeavor," said Randy 
Brinkley, Space Station Program Manager.

To begin the assembly sequence, the crew will conduct a series of 
rendezvous maneuvers similar to those conducted on other Shuttle 
missions to reach the orbiting FGB.  On the way, Currie will use 
the Shuttle's robot arm to place Node 1 atop the Orbiter Docking 
System.  Cabana will complete the rendezvous by flying Endeavour 
to within 35 feet of the FGB, allowing Currie to capture the FGB 
with the robot arm and place it on the Node's Pressurized Mating 
Adapter.

Once the two elements are docked, Ross and Newman will conduct 
two scheduled spacewalks to connect power and data cables between 
the Node, PMAs and the FGB.  The day following the spacewalks, 
Endeavour will undock from the two components, completing the 
first Space Station assembly mission.

STS-88 marks Cabana's fourth flight in space.  He has been Chief 
of the Astronaut Office since 1994.  Currie and Newman each will 
be making their third flight into space, and Ross will be making 
his sixth space flight.

For complete biographical information on the STS-88 crew and 
other astronauts, see the NASA Internet astronaut biography home 
page at URL:  http://www.jsc.nasa.gov/Bios/.

For information on the International Space Station, visit the 
Space Station home page at URL:  http://issa-www.jsc.nasa.gov/
-----------------------------------------------------------------

SEARCH FOR PAST LIFE ON MARS: POSSIBLE RELIC BIOGENIC ACTIVITY IN 
MARTIAN METEORITE ALH84001
David S. McKay, Everett K. Gibson Jr., Kathie L. Thomas-Keprta, 
Hojatollah Vali, Christopher S. Romanek, Simon J. Clemett, Xavier
D. F. Chillier, Claude R. Maechling, Richard N. Zare

[Recent news stories have announced results concerning organic 
molecules and other possible biological features found in a 
martian meteorite.  To facilitate evaluation and understanding of 
these results, Science is providing the full text of the current 
version of the paper.  The final version will be published in 
Science on 16 August, 1996.]

Fresh fracture surfaces of the martian meteorite ALH84001 contain 
abundant polycyclic aromatic hydrocarbons (PAHs).  These fresh 
fracture surfaces also display carbonate globules.  Contamination 
studies suggest that the PAHs are indigenous to the meteorite.  
High-resolution scanning and transmission electron microscopy 
study of surface textures and internal structures of selected 
carbonate globules show that the globules contain fine-grained, 
secondary phases of single-domain magnetite and Fe-sulfides.  The 
carbonate globules are similar in texture and size to some 
terrestrial bacterially induced carbonate precipitates.  Although 
inorganic formation is possible, formation of the globules by 
biogenic processes could explain many of the observed features, 
including the PAHs.  The PAHs, the carbonate globules, and their 
associated secondary mineral phases and textures could thus be 
fossil remains of a past martian biota.

D. S. McKay, Mail Code SN, NASA Lyndon B.  Johnson Space Center 
(JSC), Houston, TX 77058, USA.
E. K. Gibson Jr., Mail Code SN4, NASA-JSC, Houston, TX 77058, 
USA.
K. L. Thomas-Keprta, Lockheed Martin, Mail Code C23, 2400 NASA 
Road 1, Houston, TX 77058, USA.
H. Vali, Dept. of Earth and Planetary Sciences, McGill 
University, 3450 University St., Montreal, Quebec, H3A 2A7 
Canada.
C. S. Romanek, Savannah River Ecology Laboratory, Drawer E, 
University of Georgia, Aiken, SC 29802, USA.
S. J. Clemett, X. D. F. Chillier, C. R. Maechling, R. N. Zare, 
Department of Chemistry, Stanford University, Stanford, CA 94305-
5080, USA.

A long-standing debate over the possibility of present-day life 
on Mars was addressed by the Viking lander experiments in 1976.  
Although the results were generally interpreted to be negative 
for life in the tested surface soils, the possibility of life at 
other locations on Mars could not be ruled out (1).  The Viking 
lander's mass spectrometry experiments failed to confirm the 
existence of organics for the martian surface samples analyzed.  
Furthermore, the Viking results contained no information on 
possible fossils.  Another source of information about possible 
ancient martian life is the Shergotty-Nakhla-Chassigny (SNC) 
class of meteorites, which appear to have come to the Earth by 
impact events on Mars (2, 3).  We have examined ALH84001, 
collected in Antarctica and recently recognized as a meteorite 
from Mars (4).  Our objective was to look for signs of past 
(fossil) life within the pore space or secondary minerals of this 
martian meteorite.  Our task is difficult because we only have a 
small piece of rock from Mars and we are searching for martian 
biomarkers on the basis of what we know about life on Earth.  
Therefore, if there is a martian biomarker, we may not be able to 
recognize it, unless it is similar to an earthly biomarker.  
Additionally, no information is available on the geologic context 
of this rock on Mars.

ALH84001 is an igneous orthopyroxenite consisting of coarse-
grained orthopyroxene [(Mg,Fe)SiO3] and minor maskelynite 
(NaAlSi3O8), olivine [(Mg,Fe)SiO4], chromite (FeCr2O4), pyrite 
(FeS2), and apatite [Ca3(PO4)2] (4, 5, 6).  It crystallized 4.5 
billion years ago (Ga) (6).  It records at least two shock events 
separated by a period of annealing.  The age of the first shock 
event has been estimated to be 4.0 Ga (7).  Unlike the other SNC 
meteorites, which contain only trace carbonate phases, ALH84001 
contains secondary carbonate minerals that form globules from 1 
to ~250 m across (4, 6, 8, 9).  These carbonate globules have 
been estimated to have formed 3.6 Ga (10).  Petrographic and 
electron microprobe results (4, 11) indicate that the carbonates 
formed at relatively high temperatures ( ~700 C); however, the 
stable oxygen isotope data indicate that the carbonates formed 
between 0 and 80 C (12).  The carbonate globules are found along 
fractures and in pore spaces.  Some of the carbonate globules 
were shock-faulted (4, 5).  This shock event occurred on Mars or 
in space, and thus rules out a terrestrial origin for the 
globules (3, 8, 13).  The isotopic composition of the carbon and 
oxygen associated with the carbonate globules also indicates that 
they are indigenous to the meteorite and were not formed during 
its 13,000-year residence in the Antarctic environment (13).

The delta 13C values of the carbonate in ALH84001 range up to 42 
per mil for the large carbonate spheroids (12) and are higher 
than values for carbonates in other SNC meteorites.  The source 
of the carbon is the martian atmospheric CO2, which has been 
recycled through water into the carbonate (12).  The carbon 
isotopic compositions of ALH84001 are similar to those measured 
in CM2 carbonaceous chondrites (14).  Consequently, the 
carbonates in ALH84001 and the CM2 meteorites are believed to 
have been formed by aqueous processes on parent bodies.  The 
delta 13C in martian meteorite carbonates ranges from -17 to +42 
per mil (12, 15, 16).  This range of 13C values exceeds the range 
of 13C generated by most terrestrial inorganic processes (17, 
18).  Alternatively, biogenic processes are known to produce wide 
ranges in delta 13C on Earth (19, 20).

ALH84001 arrived on Earth 13,000 years ago (15, 21) and appears 
to be essentially free of terrestrial weathering (8).  ALH84001 
does not have the carbon isotopic compositions typically 
associated with weathered meteorites (12, 15), and detailed 
mineralogical studies (8) show that ALH84001 has not been 
significantly affected by terrestrial weathering processes.

ALH84001 is somewhat friable and breaks relatively easily along 
preexisting fractures.  It is these fracture surfaces that 
display the carbonate globules.  We analyzed freshly broken 
fracture surfaces on small chips of ALH84001 for polycyclic 
aromatic hydrocarbons (PAHs) using a microprobe two-step laser 
mass spectrometer (L2MS) (22, 23).

Polycyclic aromatic hydrocarbons.  Spatial distribution maps of 
individual PAHs on interior fracture surfaces of ALH84001 
demonstrate that both total PAH abundance and the relative 
intensities of individual species have a heterogeneous 
distribution at the 50-m scale.  This distribution appears to be 
consistent with partial geo-chromatographic mobilization of the 
PAHs (24).  The average PAH concentration in the interior 
fracture surfaces is estimated to be in excess of 1 part per 
million (25).  The PAHs were found in highest concentration in 
regions rich in carbonates.

From averaged spectra we identified two groupings of PAHs by mass 
(Fig. 1A).  A middle-mass envelope of 178 to 276 atomic mass 
units (amu) dominates and is composed mostly of simple 3- to 6-
ring PAH skeletons with alkylated homologs accounting for less 
than 10% of the total integrated signal intensity.  Principal 
peaks at 178, 202, 228, 252, and 278 amu are assigned to 
phenanthrene (C14H10), pyrene (C16H10), chrysene (C18H12), perylene 
or benzopyrene (C20H12), and anthanthracene (C22H12) (26).  A 
second weak, diffuse high-mass envelope extends from about 300 to 
beyond 450 amu.  The peak density is high and shows a periodicity 
at 14 and 2 amu.  This distribution implies that there is a 
complex mixture of PAHs whose parent skeletons have alkylated 
side chains with varying degrees of dehydrogenation; specific 
assignments are ambiguous.

[Figure Caption]
Fig. 1. (A) Averaged mass spectrum of an interior, carbonate-
rich, fracture surface of ALH84001.  The spectrum represents the 
average of 1280 individual spectra defining an analyzed surface 
region of 750 by 750 m mapped at a spatial resolution of 50 by 
50 m.  (B through E) PAH Signal intensity as a function of 
distance from the ALH84001 fusion crust for the four primary PAHs 
shown in (A).  The fusion crust fragment, which showed no 
preexisting fractures, was cleaved immediately prior to analysis 
using a stainless steel scapel and introduced in <2 minutes into 
the L2MS.  Each plot represents a section perpendicular to the 
fusion crust surface, which starts at the exterior and extends a 
distance of 1200 m inward.  The spatial resolution is 100 m 
along the section line and is the average of a 2 by 2 array of 50 
by 50 m analyses, with each analysis spot being the summed 
average of 5 time-of-flight spectra.

Contamination checks and control experiments indicate that the 
observed organic material is indigenous to ALH84001.  The 
accumulation of PAHs on the Greenland ice sheet over the past 400 
years has been studied in ice cores (27).  The total 
concentration of PAHs in the cores varies from 10 parts per 
trillion for preindustrial times to 1 part per billion for recent 
snow deposition.  Because Antarctica is in the less 
industrialized Southern Hemisphere, we may expect that 
concentrations of PAHs in Antarctic ice lie between these two 
limits.  The primary source of PAHs is anthropogenic emissions, 
which are characterized by extensive alkylation (~10-fold greater 
than that of the parent PAHs) (28) and by the presence of 
abundant aromatic heterocycles, primarily dibenzothiophene 
(C12H8S; 184 amu).  In contrast, the PAHs in ALH84001 are present 
at the part per million level (~103 to 105 times higher 
concentration) and show little alkylation, and dibenzothiophene 
was not observed in any of the samples we studied.

Analysis of Antarctic salt deposits on a heavily weathered 
meteorite (LEW 85320) by L2MS did not show the presence of 
terrestrial PAHs within detection limits, which suggests an upper 
limit for terrestrial contamination of ALH84001 of 1%.  
Measurements of four interior fragments of two Antarctic ordinary 
chondrites (ALH83013 and ALH83101) of petrologic classes H6 and 
L6 showed no evidence of indigenous PAHs.  These represent 
equivalent desorption matrix blanks; previous studies have shown 
that no indigenous organic material is present in meteorites of 
petrologic class six (29).

Studies of exterior fragments of ALH84001 with intact fusion 
crust show that no PAHs are present within the fusion crust or a 
zone extending into the interior of the meteorite to a depth of 
sim 500 m (Fig. 1, B through E).  The PAH signal increases with 
increasing depth, leveling off at sim 1200 m within the 
interior, well away from the fusion crust.  This concentration 
profile is consistent with volatilization and pyrolysis of 
indigenous PAHs during atmospheric entry of the meteorite and 
formation of a fusion crust (30), but inconsistent with 
terrestrial introduction of organic material into the interior of 
ALH84001 along cracks and pore spaces during burial in the 
Antarctic ice sheet.  These results indicate that the PAHs are 
indigenous to ALH84001.

No evidence can be found for laboratory-based contamination 
introduced during processing.  Samples for analysis were prepared 
at the meteorite clean labs at NASA Johnson Space Center and 
sealed in containers before they were transported to Stanford 
University.  A contamination study conducted prior to analysis of 
these samples showed no evidence for any PAH contamination (31).  
We also conducted experiments in which chips of ALH84001 were 
cultured in nutrient medium under aerobic and anerobic 
conditions; we found the chips to be sterile.

With the use of the L2MS technique, PAHs have been found in a 
wide range of extraterrestial materials, including carbonaceous 
and ordinary chondrites (29), interplanetary dust particles (23, 
32), and interstellar graphite grains (33).  Each material is 
characterized by differing PAH distributions reflecting the 
different environments in which the PAHs formed and their 
subsequent evolution (for example, as a result of aqueous 
alteration and thermal metamorphism).  Comparison of the mass 
distribution of PAHs observed in ALH84001 with that of PAHs in 
other extraterrestrial materials indicates that the closest match 
is with the CM2 carbonaceous chondrites (34).  The PAHs in 
ALH84001, however, differ in several respects from the CM2 
chondrites:  Low-mass PAHs such as naphthalene (C10H8; 128 amu) 
and acenaphthalene (C12H8; 152 amu) are absent in ALH84001; the 
middle-mass envelope shows no alkylation; and the relative 
intensity of the 5- and 6-ring PAHs and the relative intensity 
and complexity of the extended high-mass distribution are 
different.

On Earth, PAHs are abundant as fossil molecules in ancient 
sedimentary rocks, coal, and petroleum, where they are derived 
from chemical aromatization of biological precursors such as 
marine plankton and early plant life (35).  In such samples, PAHs 
are typically present as thousands, if not hundreds of thousands, 
of homologous and isomeric series; in contrast, the PAHs we ob 
served in ALH84001 appear to be relatively simple.  The in situ 
chemical aromatization of naturally occurring biological cyclic 
compounds in early diagenesis can produce a restricted number of 
PAHs (36).  Hence, we would expect that diagenesis of 
microorganisms on ALH84001 could produce what we observed mdash a 
few specific PAHs mdash rather than a complex mixture involving 
alkylated homologs.

Chemistry and mineralogy of the carbonates.  The freshly broken 
but preexisting fracture surfaces rich in PAHs also typically 
display carbonate globules.  The globules tend to be discoid 
rather than spherical and are flattened parallel to the fracture 
surface.  Intact carbonate globules appear orange in visible 
light and have a rounded appearance; many display alternating 
black and white rims.  Under high magnification stereo light 
microscopy or SEM stereo imaging, some of the globules appear to 
be quite thin and pancake-like, suggesting that the carbonates 
formed in the restricted width of a thin fracture.  This geometry 
limited their growth perpendicular to, but not parallel to, the 
fracture.

We selected a typical globule, ~50 m in diameter, for analysis 
by TEM and electron microprobe (37).  On the basis of backscatter 
electron (BSE) images (Fig. 2), the larger globules (>10 m) have 
Ca-rich cores (which also contain the highest Mn abundances) 
surrounded by alternating Fe- and Mg-rich bands (Fig. 3).  Near 
the edge of the globule, several sharp thin bands are present.  
The first band is rich in Fe and S, the second is rich in Mg with 
no Fe, and the third is rich in Fe and S again (Fig. 3).  
Detectable S is also present in patchy areas throughout the 
globule.

[Figure Captions]
Fig. 2.  False-color backscatter electron (BSE) image of 
fractured surface of a chip from ALH84001 meteorite showing 
distribution of the carbonate globules.  Orthopyroxene is green 
and the carbonate globules are orange.  Surrounding the Mg-
carbonate are a black rim (magnesite) and a white, Fe-rich rim.  
Scale bar is 0.1 mm.  [False color produced by C.  Schwandt] 

Fig. 3.  BSE image and electron microprobe maps showing the 
concentration of five elements in a carbonate from ALH84001.  The 
element maps show that the carbonate is chemically zoned.  Colors 
range through red, green, light blue, and deep blue, reflecting 
the highest to lowest element concentrations.  Scale bars for all 
images are 20 m.  (A) BSE image showing location of 
orthopyroxene (OPX), clinopyroxene (CPX), apatite (A), and 
carbonate (MgC, C).  Fe-rich rims (R) separate the center of the 
carbonate (C) from a Mg-rich carbonate (MgC) rim.  Region in the 
box is described in Figs. 5 and 6.  (B) Iron is most abundant in 
the parallel rims, sim 3 m across, and in a region of the 
carbonate sim 20 m in size.  (C) Highest S is associated with an 
Fe-rich rim; it is not homogeneously distributed, but rather 
located in discrete regions or hot spots in the rim.  A lower S 
abundance is present throughout the globule in patchy areas.  (D) 
Higher concentrations of Mg are shown in the Fe-poor outer region 
of the carbonate.  A Mg-rich region (MgC), sim 8 m across, is 
located between the two Fe-rich rims.  (E) Ca-rich regions are 
associated with the apatite, the Fe-rich core of the carbonate 
and the clinopyroxene.  (F) P-rich regions are associated with 
the apatite.  


In situ TEM analyses of the globule in Fig. 4 revealed that Fe- 
and Mg-rich carbonates located nearer to the rim range in 
composition from ferroan magnesite to pure magnesite.  The Fe-
rich rims are composed mainly of fine-grained magnetite ranging 
in size from ~10 to 100 nm and minor amounts of pyrrhotite (~5 
vol%) (Fig. 3, region I, and Fig. 4A).  Magnetite crystals are 
cuboid, teardrop, and irregular in shape.  Individual crystals 
have well-preserved structures with no lattice defects.  The 
magnetite and Fe-sulfide are in a fine-grained carbonate matrix 
(Fig. 4, A through C).  Composition of the fine-grained carbonate 
matrix matches that of coarse-grained carbonates located adjacent 
to the rim (Fig. 4A).

[Figure Caption]
Fig. 4.  TEM images of a thin section obtained from part of the 
same fragment shown in Fig.  3A (from the region of arrow I, Fig.  
3A).  (A) Image at low magnification showing the Fe-rich rim 
containing fine-grain magnetite and Fe-sulfide phases and their 
association with the surrounding carbonate (C) and orthopyroxene 
(OPX).  (B) High magnification of a magnetite-rich area in (A) 
showing the distribution of individual magnetite crystals (high 
contrast) within the fine-grain carbonate (low contrast).  (C) 
High magnification of a pyrrhotite-rich region showing the 
distribution of individual pyrrhotite particles (two black arrows 
in the center) together with magnetite (other arrows) within the 
fine-grained carbonate (low contrast).


High-resolution transmission electron microscopy (HRTEM) and 
energy dispersive spectroscopy (EDS) showed that the Fe-sulfide 
phase associated with the Fe-rich rims is pyrrhotite (Fig.  4C).  
Pyrrhotite particles are composed of S and Fe only; no oxygen was 
observed in the spectra.  Particles have atomic Fe/S ratios 
ranging from ~0.92 to 0.97.  The size and shape of the FeS 
particles vary.  Single euhedral crystals of pyrrhotite range up 
to sim 100 nm across; polycrystalline particles have more rounded 
shapes ranging from ~20 to 60 nm across (Fig. 4C).  HRTEM of 
these particles showed that their basal spacing is 0.57 nm, which 
corresponds to the reflection of the pyrrhotite in a 4C 
monoclinic system.  The magnetite is distributed uniformly in the 
rim, whereas the pyrrhotite seems to be distributed randomly in 
distinct domains ~5 to 10 m long (Fig. 3C).  Magnetite grains in 
ALH84001 did not contain detectable amounts of minor elements.  
In addition, these magnetite grains are single-domain crystals 
having no structural defects.

A distinct region, located toward the center of the carbonate 
spheroid but completely separate from the magnetite-rich rim 
described above, also shows accumulation of magnetite and an Fe-
rich sulfide (Fig. 3A, region II, and Fig. 5A).  This region 
displays two types of textures:  the first one is more massive 
and electron-dense under the TEM.  The second region is much less 
electron-dense and is fine-grained and porous.  The porous 
material occurs mainly in crosscutting bands and rarely in 
isolated patches.  We interpret this porous texture as a region 
in which the massive carbonate has been partially dissolved.  The 
nanometer-size magnetite and Fe-sulfide phases are everywhere 
associated with the fine-grained, porous Mg-Fe-rich carbonate.  
In the regions containing high concentrations of magnetite, 
dissolution of carbonate is evident (Fig. 5A).  In contrast to 
the magnetite-rich rim, the core area contains few magnetite 
particles.  The Fe-sulfide phases in this magnetite-poor region 
have chemical compositions similar to that of the pyrrhotite.  
However, unlike pyrrhotite grains that have a large variety of 
morphologies, most of these Fe-sulfide particles have elongated 
shapes (Fig. 5B).  We could not obtain a diffraction pattern of 
these Fe-sulfide particles because they were unstable in the 
electron beam.  Possible candidates for these Fe-sulfide minerals 
include mackinawite (FeS1-x), greigite (Fe3S4), and smythite 
(Fe9S11).  Because of the morphological similarity to terrestrial 
greigite (Fig. 5C), we suggest that these Fe-sulfide minerals are 
probably greigite (38).

[Figure Caption]
Fig. 5.  TEM images of a thin section showing the morphology of 
the Fe-sulfide phases present in ALH84001 and a terrestrial soil 
sample.  Iron sulfide phase (greigite?--Fe3S4) is located in a 
magnetite-poor region separate and distinct from the magnetite-
rich rims (Fig. 3A, arrow II).  (A) TEM of a thin section showing 
a cross section of a single carbonate crystal (large black 
regions; the apparent cleavage features are due to knife damage 
by ultramicrotomy).  A vein of fine-grained carbonate (light 
gray) is observed within the large carbonate crystal.  Possibly 
greigite and secondary magnetite (fine, dark crystals) have been 
precipitated in this fine-grained matrix.  There is a direct 
relation between the presence of carbonate dissolution and the 
concentration of the fine-grained magnetite and Fe-sulfide 
phases.  This region shows fewer Fe-rich particles, while regions 
shown in Fig.  4 contain abundant Fe-rich particles.  The 
cleavage surface of the carbonate crystal does not show any 
dissolution features (arrows); there is no evidence of structural 
selective dissolution of carbonate.  (B) A representative 
elongated Fe-sulfide particle, located in the dissolution region 
of the carbonate described in (A), is most likely composed of 
greigite.  The morphology and chemical composition of these 
particles are similar to the biogenic greigite described in (C).  
(C) High magnification of an individual microorganism within a 
root cell of a soil sample showing an elongated, multicrystalline 
core of greigite within an organic envelope.


Formation of the magnetite and iron sulfides.  The occurrence of 
the fine-grained carbonate, Fe-sulfide, and magnetite phases 
could be explained by either inorganic or biogenic processes.  
Single-domain magnetite can precipitate inorganically under 
ambient temperature and neutral pH conditions by partial 
oxidation of ferrous solutions (39).  This synthetic magnetite 
ranges in size from about 1 to more than 100 nm and is chemically 
very pure (39).  Simultaneous inorganic precipitation of 
magnetite and pyrrhotite requires strongly reducing conditions at 
high pH (40).  However, carbonate is normally stable at high pH, 
and the observed dissolution of carbonate would normally require 
low pH acidic conditions.  It is possible that the Fe-sulfides, 
magnetite, and carbonates all formed under high pH conditions, 
and the acidity changed at some point to low pH., causing the 
partial dissolution of the carbonates.  But the Fe-sulfide and 
magnetite do not appear to have undergone any corrosion or 
dissolution, which would have likely occurred under acidic 
conditions (41).  Moreover, as previously mentioned, the 
dissolution of carbonate is always intimately associated with the 
presence of Fe-sulfides and magnetite.  Consequently, neither 
simultaneous precipitation of Fe-sulfides and magnetite along 
with dissolution of carbonates nor sequential dissolution of 
carbonate at a later time without concurrent dissolution of Fe-
sulfides and magnetite seems plausible in simple inorganic 
models, although more complex models could be proposed.

In contrast, the coexistence of magnetite and Fe-sulfide phases 
within partially dissolved carbonate could be explained by 
biogenic processes, which are known to operate under extreme 
disequilibrium conditions.  Intracellular coprecipitation of Fe-
sulfides and magnetite within individual bacteria has been 
reported (42).  In addition, extracellular biomediated 
precipitation of Fe-sulfides and magnetite can take place under 
anaerobic conditions (43, 44).

Magnetite particles in ALH84001 are similar (chemically, 
structurally, and morphologically) to terrestrial magnetite 
particles known as magnetofossils (45), which are fossil remains 
of bacterial magnetosomes (46) found in a variety of sediments 
and soils (41, 47, 48) and classified as single-domain (~20 to 
100 nm) or superparamagnetic (<20 nm) magnetite (49).  Single-
domain magnetite has been reported in ancient limestones and 
interpreted as biogenic (48).  Some of the magnetite crystals in 
the ALH84001 carbonates resemble extracellular precipitated 
superparamagnetic magnetite particles produced by the growth of 
anaerobic bacterium strain GS-15 (43).

Surface features and origin of the carbonates.  We examined 
carbonate surfaces on a number of small chips of ALH84001 with 
the use of high-resolution SEM (50).  The Fe-rich rim of globules 
typically consists of an aggregate of tiny ovoids intermixed with 
small irregular to angular objects (Fig. 6A).  Ovoids in the 
example are about 100 nm in longest dimension, and the irregular 
objects range from 20 to 80 nm across.  These features are 
typical of those on the Fe-rich rims of many carbonate globules.  
These objects are similar in size and shape to features in the 
Fe-rich rims identified as magnetite and pyrrhotite (Fig.  4, B 
and C).  These objects are too small to obtain compositional 
analysis under the SEM.  

[Figure Caption]
Fig. 6.  High-resolution SEM images showing ovoid and elongate 
features associated with ALH84001 carbonate globules.  (A) 
Surface of Fe-rich rim area.  Numerous ovoids, about 100 nm in 
diameter, are present (arrows).  Tubular-shaped bodies are also 
apparent (arrows).  Smaller angular grains may be the magnetite 
and pyrrhotite found by TEM.  (B) Close view of central region of 
carbonate (away from rim areas) showing textured surface and 
nanometer ovoids and elongated forms (arrows).


In the center of some of the globules (Fig. 2), the surface of 
the carbonate shows an irregular, grainy texture.  This surface 
texture does not resemble either cleavage or a growth surface of 
synthetic and diagenetic carbonates (51).  These surfaces also 
display small regularly shaped ovoid and elongated forms ranging 
from about 20 to 100 nm in longest dimension (Fig. 6B).  Similar 
textures containing ovoids have been found on the surface of 
calcite concretions grown from Pleistocene ground water in 
southern Italy (52), where they are interpreted as nanobacteria 
that have assisted the calcite precipitation.

The origin of these textures on the surface of the ALH84001 
carbonates (Fig. 6, A and B) is unclear.  One possible 
explanation is that the textures observed on the carbonate 
surface are a result of the partial dissolution of the carbonate 
mdash that is, they are erosional remnants of the carbonate that 
happen to be in the shape of ovoids and elongate forms, perhaps 
because the carbonate has preferentially eroded along grain 
boundaries or dislocations.  Shock effects may have enhanced such 
textures.  However, because we know of no similar example from 
the terrestrial geologic record or from laboratory experiments, 
we cannot fully evaluate this possible explanation for the 
textures.  A second possibility is that artifacts can be created 
during sample preparation or may result from laboratory 
contamination.  For example, the application of a thick Au-
conductive coating can produce textures resembling mud cracks, 
and even droplets or blobs of Au.  Laboratory contamination can 
include dust grains, residue from sample cleaning, and organic 
contamination from epoxy.  For comparison, we examined several 
control samples treated identically to the meteorite chips.  We 
conclude that the complex textures (Fig. 6) did not result from 
procedures used in our laboratory.  Only interior or freshly 
broken surfaces of chips were used (50).  We did observe an 
artifact texture from our Au-Pd conductive coating that consists 
of a mud crack-like texture visible only at 50,000 magnification 
or greater.  None of the controls display concentrations or blobs 
of coating material.  A lunar rock chip carried through the same 
procedures and examined at high magnification showed none of the 
features seen in Fig. 6.

An alternative explanation is that these textures, as well as the 
nanosize magnetite and Fe-sulfides, are the products of 
microbiological activity.  It could be argued that these features 
in ALH84001 formed in Antarctica by biogenic processes or 
inorganic weathering.  It is unlikely that reduced phases, such 
as iron sulfides, would form in Antarctica during inorganic 
weathering because reported authigenic sulfur-bearing phases from 
Antarctic soils and meteorites are sulfates or hydrated sulfates.  
In general, authigenic secondary minerals in Antarctica are 
oxidized or hydrated (53).  The lack of PAHs in the other 
analyzed Antarctic meteorites, the sterility of the sample, and 
the nearly unweathered nature of ALH84001 argue against an 
Antarctic biogenic origin.  As a control we examined three 
Antarctic ordinary chondrites (ALH78119, ALH76004, and ALH81024, 
all of which do not have indigenous PAHs) from the same ice field 
where ALH84001 was collected, as well as a heavily weathered 
ordinary chondrite that gave negative results for PAHs (LEW 
85320).  These meteorites were chosen to cover the different 
degrees of weathering observed on Antarctic meteorites.  
Examination of grain surfaces at all magnifications in weathered 
and unweathered regions of these meteorites showed no sign of the 
ovoid and elongate forms seen in ALH84001.  However, none of 
these control meteorites contained detectable carbonate.

Ovoid features in Fig. 6 are similar in size and shape to 
nannobacteria in travertine and limestone (54).  The elongate 
forms (Fig. 6B) resemble some forms of fossilized filamentous 
bacteria in the terrestrial fossil record.  In general, the 
terrestrial bacteria microfossils (55) are more than an order of 
magnitude larger than the forms seen in the ALH84001 carbonates.

The carbonate globules in ALH84001 are clearly a key element in 
the interpretation of this martian meteorite.  The origin of 
these globules is controversial; Harvey and McSween (11) and 
Mittlefehldt (4) argued, on the basis of microprobe chemistry and 
equilibrium phase relationships, that the globules were formed by 
high-temperature metamorphic or hydrothermal reactions.  
Alternatively, Romanek et al. (12) argued on the basis of 
isotopic relationships that the carbonates were formed under low-
temperature hydrothermal conditions (56).  The nanophase 
magnetite and Fe-sulfides present in these globules would likely 
not be detected in microprobe analyses, which normally have a 
spatial resolution of about 1 m.  Our TEM observations and our S 
maps suggest that nanophase magnetite and Fe-sulfides, while 
concentrated in some zones, are present in discrete regions 
throughout the globules.  The effect of these undetected oxide 
and sulfide minerals on the carbonate microprobe analyses may 
make the interpretation of the microprobe data (4, 11) uncertain.  
Alternatively, if the globules are products of biologic activity, 
a low-temperature formation would be indicated.  The textures of 
the carbonate globules are similar to bacterially induced 
carbonate crystal bundle precipitates produced in the laboratory 
and in a freshwater pond (57).  Moreover, the observed sequence 
in the martian carbonate globules--Mn-containing carbonate 
production early (in the core) followed by Fe carbonate and 
finishing with the abundant production of reduced Fe-sulfides, is 
a sequence that is common in terrestrial settings, because Mn is 
first reduced by biogenic action, followed by ferric iron and 
sulfate (57).  Pure Mg-carbonate (magnesite) can also be produced 
by biomineralization under alkaline conditions (59).  On the 
basis of these observations, we interpret that the carbonate 
globules have a biogenic origin and were likely formed at low 
temperatures.

It is possible that all of the described features in ALH84001 can 
be explained by inorganic processes, but these explanations 
appear to require restricted conditions mdash for example, 
sulfate-reducing conditions in Antarctic ice sheets, which are 
not known to occur.  Formation of the described features by 
organic activity in Antarctica is also possible, but such 
activity is only poorly understood at present.  However, many of 
the described features are closely associated with the carbonate 
globules which, based on textural and isotopic evidence, were 
likely formed on Mars before the meteorite came to Antarctica.  
Consequently, the formation of possible organic products 
(magnetite and Fe-sulfides) within the globules is difficult to 
understand if the carbonates formed on Mars and the magnetite and 
Fe-sulfides formed in Antarctica.  Additionally, these products 
might require anerobic bacteria, and the Antarctic ice sheet 
environment appears to be oxygen-rich; ferric oxide formed from 
metallic Fe is a common weathering product in Antarctic 
meteorites.

In examining the martian meteorite ALH84001 we have found that 
the following evidence is compatible with the existence of past 
life on Mars: (i) an igneous Mars rock (of unknown geologic 
context) that was penetrated by a fluid along fractures and pore 
spaces, which then became the sites of secondary mineral 
formation and possible biogenic activity; (ii) a formation age 
for the carbonate globules younger than the age of the igneous 
rock; (iii) SEM and TEM images of carbonate globules and features 
resembling terrestrial microorganisms, terrestrial biogenic 
carbonate structures, or microfossils; (iv) magnetite and iron 
sulfide particles that could have resulted from oxidation and 
reduction reactions known to be important in terrestrial 
microbial systems; and (v) the presence of PAHs associated with 
surfaces rich in carbonate globules.  None of these observations 
is in itself conclusive for the existence of past life.  Although 
there are alternative explanations for each of these phenomena 
taken individually, when they are considered collectively, 
particularly in view of their spatial association, we conclude 
that they are evidence for primitive life on early Mars.


References and Notes

1. P. Mazur et al., Space Sci. Rev. 22, 3 (1978); H. P. Klein, 
Eos 76, 334 (1995).

2. H. J. Melosh, Icarus 59, 234 (1984); B. J. Gladman, J. A. 
Burns, M. Duncan, P. Lee, H. F. Levison, Science 271, 1387 
(1996).

3. H. P. McSween Jr., Meteoritics 29, 757 (1994). Analyses of the 
gases in glassy inclusions in the SNC meteorites EET79001 by 
Bogard and Johnson [Science 221, 651 (1983)], Becker and Pepin 
[Earth Planet. Sci. Lett. 69, 225 (1983)], and Marti et al.  
[Science 267, 1981 (1995)] have shown that the abundance and 
isotopic compositions of the trapped gases in the SNC meteorites 
and the measured atmospheric compositions on Mars, measured in 
situ by the Viking landers, have a direct one-to-one correlation 
(more than nine orders of magnitude in concentrations). This 
remarkable agreement is one of the strongest arguments that the 
SNC meteorites represent samples from Mars.

4. D. W. Mittlefehldt, Meteoritics 29, 214 (1994).

5. A. H. Treiman, ibid. 30, 294 (1995) .

6. E. Jagoutz, A. Sorowka, J. D. Vogel, H. Wanke, ibid. 29, 478 
(1994) ; L. E. Nyquist, B. M. Bansal, H. Wiesmann, C. Y. Shih, 
Lunar Planet. Sci. 26, 1065 (1995).

7. R. D. Ash, S. F. Knott, G. Turner, Nature 380, 57 (1996) .

8. S. J. Wentworth and J. L. Gooding, Lunar Planet. Sci. 26, 1489 
(1995).

9. K. L. Thomas et al., ibid., p. 1409.

10. S. K. Knott, R. D. Ash, G. Turner, ibid., p. 765.

11. R. Harvey and H. P. McSween Jr., Nature 382, 49 (1996) .

12. C. S. Romanek et al., ibid. 372, 655 (1994) .

13. J. L. Gooding, Icarus 99, 28 (1992).

14. M. M. Grady, I. P. Wright, P. K. Swart, C. T. Pillinger, 
Geochim.  Cosmochim. Acta 52, 2855 (1988).

15. A. J. T. Jull, C. J. Eastoe, S. Xue, G. F. Herzog, 
Meteoritics 30, 311 (1995).

16. R. H. Carr, M. M. Grady, I. P. Wright, C. T. Pillinger, 
Nature 314, 248 (1985) ; I. P. Wright, C. P. Hartmetz, C. T. 
Pillinger, J. Geophys. Res. 98, 3477 (1993).

17. A. J. T. Jull, S. Cloudt, C. J. Eastoe, Lunar Planet. Inst. 
Tech.  Rep. 96-01, part 1 (Lunar and Planetary Institute, 
Houston, TX, 1996), p. 22; J. D. Hudson, J. Geol. Soc. London 
133, 637 (1977).

18. I. D. Clark and B. Lauriol, Chem. Geol. 102, 217 (1992); N. 
Nakai, H. Wada, Y. K. Iyosu, M. Takimoto, Geochem. J. 9, 7 
(1975).

19. K. J. Murata, I. Friedman, B. M. Madsen, U.S. Geol. Surv. 
Prof. Pap. 614B, 1 (1969); A. M. Martini, L. M. Walter, J. M. 
Budai, T. C. W. Ku, Geol. Soc. Am. Abstr. Prog. 27, A292 (1995);
G. E. Claypool and I. R. Kaplan, in Natural Gases in Marine 
Sediments, I. R. Kaplan, Ed. (Plenum, New York, 1974), pp. 99-
139.

20. T. O. Stevens and J. P. McKinley, Science 270, 450 (1995) .

21. Prior to landing in the Antarctic ice field, this meteorite 
was in space for about 16 million years, based on cosmic ray 
exposure data [D. D. Bogard, Lunar Planet. Sci. 26, 143 (1995)].

22. L2MS was used to analyze fresh fractured samples of ALH84001 
for the presence of PAHs. The L2MS instrument is capable of the 
simultaneous measurement of all PAHs present on a sample surface 
to a spatial resolution of 40 m, and detection limits are in the 
sub-attomole (>107 molecules) range (1 amol = 10 - 18 mol).

23. S. J. Clemett, C. R. Maechling, R. N. Zare, P. D. Swan, R. M.  
Walker, Science 262, 721 (1993) .

24. M. R. Wing and J. L. Bada, Geochim. Cosmochim. Acta 55, 2937 
(1991).

25. PAH concentration is estimated from comparison of the 
averaged spectra of interior fracture surfaces of ALH84001 with 
known terrestrial standards and the Murchison (CM2) meteorite 
matrix. In the case of Murchison (CM2), the total concentration 
of PAHs has been independently measured to be in the range of 18 
to 28 parts per million [K. L. Pering and C. Ponnamperuma, 
Science 173, 237 (1971)]. The average PAH spectrum of ALH84001 
used in this estimate was generated from the average of sim 4000 
single-shot spectra acquired from three separate fracture 
surfaces encompassing an analyzed surface area of ~2 mm2, 
representing regions both rich and poor in PAHs.

26. At a single laser ionization wavelength, L2MS is unable to 
distinguish between structural isomers; however, because 
different isomers have different photoionization cross sections, 
mass assignments are based on the most probable isomer. In the 
case of masses 178 and 202, the possible isomer combinations are 
phenanthrene or anthracene and pyrene or fluoranthene. At the 
photoionization wavelength used in this study (266 nm), the L2MS 
instrument is ~19 times as sensitive to phenanthrene as to 
anthracene and ~23 times as sensitive to pyrene as to 
fluoranthene [R. Zenobi and R. N. Zare, in Advances in 
Multiphoton Processes and Spectroscopy, S. H. Lin, Ed. (World 
Scientific, Singapore, 1991), vol. 7, pp. 1-167]. Hence, masses 
178 and 202 are assigned to phenanthrene and pyrene. In the case 
of higher masses, more structural isomers exist, and assignments 
are based on those PAHs known to have high cross sections from 
comparisons with standards.

27. K. Kawamura and I. Suzuki, Naturwissenschaften 81, 502 
(1994).

28. W. W. Youngblood and M. Blumer, Geochim. Cosmochim. Acta 39, 
1303 (1975); S. T. Wakeham, C. Schaffner, W. Giger, ibid. 44, 403 
(1980) ; R. E. LaFlamme an d R. A. Hites, ibid. 42, 289 (1978) ;
T. E. Jensen and R. A. Hites, Anal. Chem. 55, 594 (1983) .
29. S. J. Clemett, C. R. Maechling, R. N. Zare, C. M. O. D. 
Alexander, Lunar Planet. Sci. 23, 233 (1992); L. J. Kovalenko et 
al., Anal.  Chem. 64, 682 (1992).

30. The interiors of stony meteorites are not heated above 100 to 
120 C during passage through the Earth's atmosphere. For example, 
in the CM carbonaceous chondrite Murchison, amino acids have been 
found by Kvenvolden et al. [Nature 228, 923 (1970)]. If 
temperatures had been above 120 C, amino acids would have 
degraded.

31. Sources of laboratory contamination fall into three 
categories:  sample handling, laboratory air, and virtual leaks 
(that is, sources of PAHs inside the L2MS vacuum chamber). 
Possible contamination during sample preparation was minimized by 
performing nearly all sample preparation at the NASA-JSC 
meteorite curation facility. In cases where subsequent sample 
handling was required at Stanford, all manipulation was performed 
in less than 15 minutes, using only stainless steel tools 
previously rinsed and ultrasonicated in methanol and acetone. 
Dust-free gloves were worn at all times and work was performed on 
a clean aluminum foil surface. To quantify airborne contamination 
from exposure to laboratory air, two clean quartz discs were 
exposed to ambient laboratory environments both at NASA-JSC and 
Stanford. Each disc received an exposure typical of that 
experienced subsequently by samples of ALH84001 during sample 
preparation. No PAHs were observed on either quartz disk at or 
above detection limits.  Because contamination can depend on the 
physical characteristics of the individual sample (for example, a 
porous material will likely give a larger contamination signal 
than a nonporous one), additional contamination studies have been 
previously conducted at Stanford [see (29)]. Briefly, samples of 
the meteoritic acid residues of Barwell (L6) and Bishunpur (L3.1) 
were exposed to laboratory air for 1 and 4 days, respectively. 
Barwell (L6) is known to contain no indigenous PAHs and none were 
observed on the exposed sample. Bishunpur (L3.1), in contrast, 
contains a rich suite of PAHs, but no discernible differences in 
signal intensities were observed between exposed and unexposed 
samples.  To test for contamination from virtual leaks, the L2MS 
instrument was periodically checked using samples of Murchison 
(CM2) meteorite matrix whose PAH distribution has been previously 
well characterized. No variations in either signal intensity or 
distribution of PAHs were observed for L2MS instrument exposure 
times in excess of 3 days. No sample of ALH84001 was in the 
instrument for longer than 6 hours. The L2MS vacuum chamber is 
pumped by an oil-free system: two turbomolecular pumps and a 
liquid-nitrogen-cooled cyropump.

32. K. L. Thomas et al., Geochim. Cosmochim. Acta 59, 2797 
(1995).

33. S. J. Clemett, S. Messenger, X. D. F. Chillier, X. Gao, R. M.  
Walker, R. N. Zare, Lunar Planet. Sci. 26, 229 (1996).

34. S. J. Clemett, thesis, Stanford University (1996).

35. B. P. Tissot and D. H. Welte, Petroleum Formation and 
Occurrence (Springer, New York, 1978).

36. R. E. LaFlamme an d R. A. Hites, Geochim. Cosmochim. Acta 42, 
289 (1978); S. G. Wakeham, C. Schaffner, W. Giger, ibid. 44, 415 
(1980) .

37. We removed the spheroid from a thin section with a micro-
coring device, embedded it in epoxy, thin sectioned it using an 
ultramicrotome, and analyzed it using a TEOL 2000FX TEM 
[technique described in (31)]. We made about 50 thin sections 
from the globule, and the remaining carbonate globule was coated 
with evaporated carbon for conductivity (~10 nm) and mapped with 
wavelength dispersive spectroscopy for major and minor elements, 
using a Cameca SX 100 microprobe (Fig. 3).

38. H. Stanjek, J. W. E. Fassbinder, H. Vali, H. Wegele, W. Graf, 
Eur. J. Soil Sci. 45, 97 (1994).

39. B. A. Maher, in Iron Biominerals, R. B. Frankel and
R. P. Blakemore, Eds. (Plenum, New York, 1991), p. 179; R. M.  
Taylor, B. A. Maher, P. G. Self, Clay Miner. 22, 411 (1987).

40. H. G. Machel, in Palaeomagnetic Applications in Hydrocarbon 
Exploration and Production, P. Turner and A. Turner, Eds. (Geol.  
Soc. Spec. Publ. 98, Geological Society, London, 1995), pp. 9-29;
R. M. Garrels and C. L. Christ, Solutions, Minerals and 
Equilibria, (Freeman, Cooper, San Francisco, 1969).

41. H. Vali and J. L. Kirschvink, Nature 339, 203 (1989) ; H. 
Vali, O.  Forster, G. Amarantidis, N. Petersen, Earth Planet. 
Sci. Lett. 86, 389 (1987).

42. H. Vali and J. L. Kirschvink, in Iron Biominerals, R. B. 
Frankel and R. B. Blakemore, Eds. (Plenum, New York, 1990, pp. 
97-115; S.  Mann, N. H. C. Sparks, R. B. Frankel, D. A. 
Bazylinski, H. W. Jannasch, Nature 343, 258 (1990) ; M. Farina, 
D. M. Esquivel, H. G. P. L. de Barros, ibid., p. 256 (1990); D. 
A. Bazylinski, B. R. Heywood, S. Mann, R. B. Frankel, ibid. 366, 
218 (1993); A. Demitrac, in Magnetite Biomineralization and 
Magnetoreception, J. Kirschvink, D. S. Jones, B. J. McFadden, 
Eds. (Plenum, New York, 1985, pp. 625-645); R. B. Frankel and R. 
B. Blakemore, Eds.  Iron Biomineralization (Plenum, New York, 
1991).

43. D. R. Lovely, J. F. Stolz, G. L. Nord Jr., E. J. P. Phillips, 
Nature 330, 252 (1987) .

44. D. Fortin, B. Davis, G. Southam, T. J. Beveridge, J. Indust.  
Microbiol. 14, 178 (1995).

45. J. L. Kirschvink and S. B. R. Chang, Geology 12, 559 (1984).

46. R. P. Blakemore, Annu. Rev. Microbiol. 36, 217 (1982).

47. N. Petersen, T. von Dobeneck, H. Vali, Nature 320, 611 (1986) 
; J. W. E. Fassbinder, H. Stanjek, H. Vali, ibid. 343, 161 
(1990).

48. S. R. Chang, J. F. S. Tolz, J. L. Kirschvink, S. M. Awramik, 
Precambrian Res. 42, 305 (1989).

49. R. F. Butler and S. K. Banerjee, J. Geophys. Res. 80, 4049 
(1975).

50. We handpicked small chips in a clean bench from our 
curatorial allocation of ALH84001. Most chips were from a region 
near the central part of the meteorite and away from the fusion 
crust, although for comparison we also looked at chips containing 
some fusion crust. For high-resolution work we used an Au-Pd 
coating estimated to be ~2 nm thick in most cases. On some 
samples we used a thin (<1 nm) coating, about 10 s with our 
sputter coater; these samples usually showed charging effects and 
could not be used for highest resolution imaging. We more 
typically used 20 to 30 s. For backscatter and chemical mapping 
we used a carbon coat of about 5 to 10 nm thick. We monitored the 
possible artifacts from the coating using other reference samples 
or by looking at fresh mineral surfaces on ALH84001. We could 
also estimate relative coating thicknesses by the size of the Au 
and Pd peaks in the energy dispersive x-ray spectrum. For our 
heaviest coating, a slight crazing texture from the coating is 
barely visible at a magnification of 50,000 on the cleanest 
fresh grain surfaces. The complex textures shown in most of the 
SEM photographs are not artifacts of the coating process but are 
the real texture of the sample. We used a JEOL 35 CF and a 
Philips SEM with a field emission gun (FEG) at the JSC. The JEOL 
and Philips SEMs are equipped, respectively, with a PGT and Link 
EDS system. We achieved about 2.0 nm resolution at 30kV. Some 
images were also taken at lower kV, ranging from 1 to 10 kV. In 
most cases, the chips were coated after handpicking with no 
further treatment. For comparison, several chips were 
ultrasonically cleaned for a few seconds in liquid Freon before 
coating to remove adhering dust.  Several samples were examined 
uncoated at low kV. We carbon-coated and examined all of the 
surfaces analyzed for PAHs only after the PAH analyses had been 
completed.

51. J. Paquette, H. Vali, E. W. Mountjoy, Am. Mineral., in press;
J. Paquette, H. Vali, A. Mucci, Geochim. Cosmochim. Acta, in 
press.

52. E. F. McBride, M. Dane Picard, R. L. Folk, J. Sed. Res. A64, 
535 (1994); see fig. 9.

53. E. K. Gibson, S. J. Wentworth, D. S. McKay, Proc. 13th Lunar 
Planet. Sci. Conf., Part 2, J. Geophys. Res. 88, suppl. A912 
(1983); M. A. Velbel, Meteoritics 23, 151 (1988); I. B. Campbell 
and G. G. C. Claridge, Antarctica: Soils, Weathering Processes 
and Environment, Developments in Soil Science 16 (Elsevier, 
Amsterdam, 1987).

54. R. L. Folk, J. Sediment Petrol. 63, 990 (1993).

55. J. W. Schopf and C. Klein, Eds., The Proterozoiciment 
Biosphere (Cambridge University Press, New York, 1992).

56. Contrary to the interpretations presented by Harvey and 
McSween (11) concerning the equilibrium partitioning of stable 
carbon isotopes on Mars, delta 13C values for carbonate and 
atmospheric CO2 are incompatible with a high-temperature origin. 
For the CaCO3-CO2 system, solid carbonate is only enriched in 13C 
below about 200 C [T. Chacko, T. K. Mayeda, R. N. Clayton, J. R.  
Goldsmith, Geochim. Cosmochim. Acta 55, 2867 (1991); C. S.  
Romanek, E. L. Grossman, J. W. Morse, ibid. 56, 419 (1992)].  
Assuming the delta 13C of ambient CO2 is 27 per mil (the value for 
trapped gases in the martian meteorite EETA79001) [C. P. 
Harzmetz, I. P. Wright, C. T. Pillinger, in Workshop on the Mars 
Surface and Atmosphere Through Time, R. M. Haberle et al., Eds. 
(Tech. Rep.  92-02, Lunar and Planetary Institute, Houston, TX, 
1992), pp.  67-68], a delta 13C of 42 per mil for carbonate in 
ALH84001 can only be explained by a precipitation temperature 
around 0 C. This temperature estimate is compatible with an 
independent range of precipitation temperatures (0 to 80 C) based 
on the delta 18O of the same carbonates (12). If carbon isotopes 
are distributed heterogeneously on Mars in isolated reservoirs 
(for example, the crust and atmosphere), precipitation 
temperature estimates based on stable isotopes are relatively 
unconstrained. This is probably not the case, though, as other 
researchers [(3); L. L. Watson, I. D. Hutcheon, S. Epstein, E. M. 
Stolper, Science 265, 86 (1994) ; B. M. Jakosky, Geophys. Res. 
Lett. 20, 1591 (1993)] have documented a link between crustal and 
atmospheric isotopic reservoirs on the planet.

57. C. Buczynsik and H. S. Chafetz, J. Sediment Petrol. 61, 226 
(1991); also see Figs. 1D, 3, A and B.

58. K. H. Nealson and D. Saffarini, Annu. Rev. Microbiol. 48, 311 
(1994) ; J. P. Hendry, Sedimentology 40, 87 (1993).

59. J. B. Thompson and F. G. Ferris, Geology 18, 995 (1990).

60. We thank L. P. Keller, V. Yang, C. Le, R. A. Socki, M. F. 
McKay, M. S. Gibson, and S. R. Keprta for assistance; and R. 
Score and M. Lindstrom for their help in sample selection and 
preparation.  The guidance of J. W. Schopf at an early stage of 
this study is appreciated. We also thank G. Horuchi, L. Hulse, L. 
L. Darrow, D. Pierson, and personnel from Building 37. The work 
was supported in part by NASA's Planetary Materials Program 
(D.S.M. and R.N.Z.) and the Exobiology Program (D.S.M.). 
Additional support from NASA-JSC Center Director's Discretionary 
Program (E.K.G.) is recognized. C.S.R. and H.V. acknowledge 
support from the National Research Council. X.D.F.C. acknowledges 
support from the Swiss National Science Foundation.


5 April 1996; accepted 16 July 1996

Volume 273, Number 5277, Issue of 16 August 1996, pp. 924-930 
(c)1996 by The American Association for the Advancement of 
Science.
-----------------------------------------------------------------
End Marsbugs Vol. 3, No. 9.

