Around the world travel to find old rocks

Marilyn in Rajasthan, India 2009

         The work with Papineau took me to several locations around the globe to examine Precambrian rocks in the field. We traveled to Ontario and Quebec to study banded iron formations (BIFs) on a NASA Astrobiology Institute-sponsored field trip (Ohmoto et al., 2008) where a diverse team of scientists argued in the field about the levels of oxygen on early Earth, formation of banded iron formations, and isotopic compositions of billion year old rocks. One memory I have of this trip is of Dick Holland, Harvard University, and Hiroshi Ohmoto, Penn State, standing on a BIF and speaking with a bullhorn to young astrobiologists, to give their perspectives on all of these topics. My next trip with Dominic was to Rajasthan, India, where we sampled stromatolites containing commercial grade phosphates from the Aravalli Supergroup. My trip to India and my first in-depth field trip to examine stromatolites in a natural setting was a remarkable experience.

         Standing on outcrops that extended for several kilometers and that had been formed almost entirely by the actions of microbes was a highlight for me as a biogeochemist who was brought into the field by the early work of Barghoorn and others from the 1970s. My challenge was to inspect the rocks in the field and couple observations with my more reductionist approach based on isotopic measurements in the laboratory. We traveled with two Indian specialists, Professor Roy and Professor Ritesh Purohit, who had studied the geology of these formations for many years. Fieldwork in India, as opposed to other places I had worked, was never conducted without close watchfulness from local people. At the end of a 1 to 2 hour sampling, our field area would be lined with about 20 to 30 men, women, and children along with goats, water buffaloes, and cows observing our activities. 

Dominic Papineau, Marilyn, Prof. Roy, and Ritesh Purohit (left to right), India standing on stromatolites billions of years old

         Based on the samples we collected from India, we published a series of papers on the development of the Earth’s early nitrogen cycle (Papineau et al., 2013). Based on these 2.15 billion years old samples, we linked the carbon cycle to a robust nitrogen cycle at the time when atmospheric oxygen increased 2.4 billion years ago. Microbes, primarily cyanobacteria, were the producers of oxygen at that time. Not only did we measure high concentrations of organic carbon in these rocks, but their carbon isotope values were highly variable. Extreme variability in carbon isotopes is indicative of swings from low to high primary productivity by photosynthetic organisms.

         My second major field trip with Dominic Papineau was fascinating for its spectacular geology, the remoteness of the location, and the chance to interact with native people of northern Quebec. From a small village on the eastern shore of Hudson Bay we chartered a fishing boat, the Kakivak, in July 2011, that was crewed by Inuit men. My husband accompanied me and 13 other scientists along with five Inuit crew for a two-week adventure on Hudson Bay. We set sail from Umijaq on a Sunday afternoon, making our way across Hudson Bay to the Belcher Islands.  These islands are special for several reasons. First, they are very remote, and scientists have visited them only sporadically over the past 100 years. Robert Flaherty described the geological formations in 1918. Our target samples were 1.875 billion year old stromatolites that had first been found in the early 20^th century. Scientists at that time realized how special these rocks were and found evidence for the remains of microorganisms that lived on the early Earth. We returned to several of these sites, spending three days at one of the most spectacular stromatolite sections that I have ever seen. 

Wouter Bleeker lecturing on Precambrian geology

Stromatolites on Belcher islands, 2010

         Second, the islands are special because they are biologically pristine. This was the second time I was able to study and sample tundra vegetation. As the temperatures of Arctic and tundra areas increase due to climate change, plants will respond with longer growing seasons, making it important to develop records of present day communities and the processes that influence them. I was able to collect about 75 specimens from the Belcher Islands for my herbarium collection that may—some day—serve as an historic record of what the plant life was like in the early 21^st century.

         People, other than the Inuit, rarely visit the Belcher Islands, as there is no support for ecotourism in the area. We were fortunate to be able to experience Inuit culture including native fishing. Periodically, the crew fished while we were out examining rocks. They caught Arctic char which they shared with us: the muscle, Canadian sushi, went to the scientists and the rest of the fish--tongue, liver, intestines, skin, heart--was consumed raw with great relish by the crew. The Inuit understand in a very fundamental way about the ecosystem in which they live.  

Inuit crew: Captain on left, Marilyn on right

         The 2^nd week of our expedition took us back towards the mainland. We traveled to the Nastapoka Islands that form an arc parallel to the coastline, a part of the Hudson Bay considered by some to be a remnant crater from a meteorite impact. Our scientific party scoured several of these islands looking for evidence of shocked rock strata indicative of such an impact. We were unable to find samples of this nature, but could see correlations between these rocks and those on the Belcher Islands. Our 3^rd destination was the Richmond Gulf, an unbelievably beautiful body of water with high mountains, cliffs, and crystal clear waters. Our team scoured at least 7 different sites with numerous outcrops to compare the stratigraphy here with that on the Belcher Islands. Canadian Geological Survey scientist, Dr. Wouter Bleeker, took samples for dating, as there are only a handful of dates from this whole area.        

         In the Richmond Gulf, we were treated to a sighting of beluga whales, small white whales considered a delicacy by the Inuit. The pod of about 20 belugas swam into the inlet where we were moored, diving, jumping, and hunting for the abundant Arctic char. Our Inuit crew watched them carefully, but decided not to hunt owing to the fact that we had 15 people on one small boat.

         Almost 600 kg of rocks were shipped back to the United States and Ottawa for further analysis. The expedition was a lifetime experience for all of us, as we were privileged to seeing places, rocks, and people that very few people will ever have the opportunity to experience. The results from this trip are currently being written up for a publication, spear-headed by Papineau, on the nature of concretions found in Paleoproterozoic rocks and what they mean in terms of organic carbon cycling.

Marilyn and Chris, Belcher Islands

         Studies on isotopic compositions of Earth’s earliest sedimentary rocks are going to feed into studies that will consume the astrobiological community when samples from Mars are finally returned to Earth. It is vitally important for the scientific community to continue to carefully study biosignatures on the Earth weighing what is a definite biosignature versus an ambiguous one.  The personalities that study Earth’s oldest rocks are quite strong; individuals hold strong opinions. There is a constant push and pull to announce the first evidence of life on Earth, similar to the desire to find the signs of life on Mars.

"Slatering" or How to confuse pesky colleagues

Page Chamberlain (green shirt, center) and Marilyn (to his right with shorts and skinny), Geophysical Lab on Upton St., circa 1988

            In 1996, I spent a short sabbatical at Dartmouth College interacting with Page Chamberlain and his lab group. I taught a 1-month long course on Organic Geochemistry to a full class of bright undergrad and grad students. Page had been a postdoc at the Geophysical Lab in the late 1980s. A recent Harvard grad, Chamberlain had a wife and small baby and was desperate to move out of their small apartment in DC to more comfortable surroundings. Page taught me how to use the very dangerous, potentially explosive, bromine pentafluoride vacuum line for analyzing oxygen isotope in rock samples. He was a thorough teacher, but had a nervous tic in his right eye that wouldn’t go away. At that time, given the stresses in his life, he was largely humorless. He landed a plum job at Dartmouth and was substantially relieved.

            Years later, at a Geological Society of America meeting, I saw Page at the annual Harvard-MIT cocktail party. He’d had a drink or three and blurted out that I was one person he was “afraid of”. Page has a commanding presence, is well over 6 feet tall, bald, and not a shrinking violet. We decided then and there that we needed to fix the fear feeling and get to know each other better. Hence, we planned the sabbatical. My children, Dana and Evan, and I moved into one of his son's bedrooms in the Chamberlains’ large, white colonial house, three blocks from campus. The house was filled with numerous pets: two unruly Labrador retrievers, a large iguana named Mikey, a rouge cat, numerous fish, and some sort of slimy shrimp growing in a bowl on the kitchen counter. Page’s wife Margaret Dyer-Chamberlain ran the household. I was pleasantly surprised to learn that Page had loosened up completely and was now known, not only for his brilliance in geochemistry, but for knowing how to not take himself too seriously. He can be enormously funny.

            Often after my lectures, we’d sit and talk about things. As an inexperienced lecturer, Page offered advice on how to deal with questions that you didn’t know the answer to. “I Slater them,” he explained to me.

            “If a student asks a question and you don’t feel like answering, look at them seriously over your glasses and say ‘ I believe Slater wrote the definitive paper on that in the 1960s. You should know about that.’ They then go away and spend a few days trying to find the seminal article by Slater.”

Derek Smith and Andrew Steele, UC Merced 2015

            “What happens then?” I asked.

            “When they return, if they do, ask if they looked for the correct Slater paper. Was it John F. Slater or his brother Frank Slater from Yale? Were they sure they searched the literature thoroughly? Send ‘em off again,” he answered.

            “And the third time?” I inquired.

            “Mention that Slater won a serious prize, not the Nobel—too easy to check—but another prize less well known. You can add that Slater had cancer in the late 1980s and ask the student if he was still alive. They’ll go away at this point and not come back, thinking they’re idiots.”

            We professors at public universities couldn’t easily get away with this. But I could see some value in teaching a student to think critically and read the literature. I’ve “Slatered” a few people in my career, most notably a young whipper-snapper from Paul Koch’s lab. Seth Newsome, Paul’s student at UC Santa Cruz, was giving a talk at the Isotope Ecology meeting in Flagstaff, Arizona, in 2004. I was chairing the session. Seth ended his talk by saying that he interpreted his data in a non-scientific way sometimes. Not knowing what that meant I asked. In front of the entire conference, this upstart “kid” answered, “I’ll tell you all about it, when I come over to your house tonight.” The audience laughed. I turned bright red.

            He was referring to a house party the Carnegie/Smithsonian people were holding that evening, not—as others assumed—a private, candlelight meeting. People asked, “Who was that guy?” When he came to the party later that evening, we were ready. I started, “Seth, I assume you’ve looked at Slater’s work on seals and isotopes. He published early in the 1960s. I think he found similar trends to yours.” My colleague Noreen Tuross followed. “Yeah, that was an OK paper, but Slater’s best work was in the ‘70s with his son Slater Jr. Have you seen that one?” The other Carnegie postdocs nodded sagely. Some said, “That was a special paper Slater and Slater, 1978.”

            Seth shook his head. We saw him mentally jot down the name of Slater. Throughout the evening, we kept it up. Finally, by midnight, he was let in gently that he’d been “Slatered”.

 Marilyn and Seth Newsome, wombat hunting, South Australia, 2008

            In 2005, when I had a postdoc position to work on wombats in Australia, he was my first choice. We’ve been working together ever since—a great scientist and a perfect colleague and friend. More stories on Seth will follow.

Earth’s Earliest Signs of Life: If we found it, could we recognize it?

Dina Bower (left), unidentified young astrobiologist, Jim Cleaves, Verena Starke--the next generation learning to look at ancient rocks

         Since the early 1970s, scientists have been measuring the amount and nature of organic carbon from almost 4 billion year old Precambrian rocks. Geologists were searched the world over for older and older rocks resting exposed on the surface that might contain evidence of the first signs of life. Greenland’s coasts have a couple of small deposits of some of the Earth’s oldest rocks. For example, the Isua formation was thought to have formed in a sedimentary environment 3.85 billion years ago. In the 1980s, Cyril Ponneperuma and his student Cliff Walters of the University of Maryland examined the organic geochemistry of these rocks to find the evidence of the first living organisms.

         Professor Ponneperuma wanted Cliff to discover something revolutionary. Cliff struggled at the University of Maryland to find any molecules that did not look like modern contamination, but his professor pressured him to “discover” something big. Fortunately for Cliff, he sought out the wisdom of Tom Hoering. Hoering’s reputation for careful, exacting work was well known in the geochemistry community, particularly after he debunked an earlier study on “Precambrian” hydrocarbons, which turned out to be ink from the newspapers wrapping the rock specimens. Walters finally concluded that any molecular signals in these samples were contamination. He went on to become a very successful petroleum organic geochemist at Exxon Mobil, having learned from Tom Hoering about stringent lab procedures.

         A decade later, UCLA scientists, including Stephen Mojzsis, used more sophisticated instrumentation to measure carbon isotope signals directly in the rocks (i.e. in situ) with an instrument called an ion probe, a multi-million dollar combination mass spectrometer and microscope.  A beam of strong positive ions, charged particles, bombard the polished surface of a rock sample. Elements from the rock were sputtered off the surface then accelerated through a high vacuum flight tube where they were separated and measured. The ion probe was promoted as the solution to answering the question of whether the carbon in ancient rocks was indigenous to the sample or was caused by contamination. The UCLA group measured carbon isotope signals (Mojzsis et al., 1996) in Isua samples, concluding that they were in the range of similar measurements from much younger, firmly established Precambrian stromatolite samples.

         The problem with the ion probe measurements was that there were no comparable working standards. As time went on, ion probe users realized they needed to be much more careful about how their instruments were standardized. Dominic Papineau, a postdoctoral fellow at the Geophysical Laboratory, compared “conventional” elemental analyzer methods with ion probe methods to learn more about the standards needed for accurate and precise carbon isotope analyses (Papineau et al., 2010b) using Akilia rocks, from southwestern Greenland. 

Clark Johnson studying Canadian banded iron formations, 2007

         Dominic Papineau, a French Canadian, was a graduate student at the University of Colorado training with Stephen Mojzsis, now a professor there. Dominic wrote to me midway in his doctoral work and asked if would be one his dissertation committee. I readily agreed. Steve Mojzsis has quite a reputation for speaking his mind at scientific conferences. A bright, well-spoken man, he can argue a point with great skill, which he does. Dominic, in learning from his professor, tried to emulate Mojzsis, but as a student, he wasn’t ready to take on senior scientists in public. Papineau came to the Geophysical Lab as a postdoc working with me and opened many new doors for research and collaboration. With a bit of a swagger, he worked hard trying to deal with opinions and speculations about the Earth’s oldest rocks. We remain colleagues to this day.

         Several papers were published on the Akilia “rocks” (e.g., McKeegan et al., 2007), however, there are only a handful of specimens from this location and no real outcrop that can be studied by the community. Therefore, few samples can be shared among labs.  Speculation and debate about what type of rocks these are and how they were formed abounds. Dominic obtained a couple of the Akilia specimens from his Ph.D. advisor Stephen Mojzsis. Our first paper together was based primarily on microscopic analyses using Raman spectroscopy, transmission electron microscopy, and Synchrotron X-ray based microscopy (Papineau et al., 2010a). Papineau studied graphite inclusions in association with apatite crystals, phosphate minerals common in many types of rocks.

         Andrew Steele and I encouraged him to quantify the occurrences of graphite-apatite pairs rather than loosely describing them. Were these common features? Were there only one or two within a thin section? Did they all present the same appearance? About one-sixth of the apatite crystals were associated with a graphite coating. The graphitic carbon was primarily ordered graphite, with a much smaller amount of disordered carbon. Raman spectroscopy was also used to determine that the graphite in these rocks was crystallized at very high temperatures during metamorphism (>650°C). The carbon was severely reordered making it impossible to determine if it was originally biogenic or abiogenic carbon.

         It is important for scientists to debate and ultimately come to an agreement on the first conclusive evidence of life on Earth. Many researchers use the carbon isotope compositions of graphite from Earth’s oldest rocks as firm evidence that photosynthesis was an active process 3.85 billion years ago. Others argue that owing to metamorphic processes, graphitic carbon in ancient rocks could result from numerous types of abiogenic reactions that show carbon isotope compositions similar to photosynthetic ones. This distinction is important because we want to know how to identify very old signs of life after we have sufficient samples from Mars and other planetary bodies. We still struggle to find an unambiguous signal of first life on Earth.

Nancy Drew and the Mystery of the Disappearing Nitrogen

Ed Young (left) and Doug Rumble (right) with isotope vacuum line requiring liquid nitrogen, circa 1993

            Every workplace has its dose of office politics. The Carnegie’s Geophysical Laboratory was no exception. As just a rank-and-file staff scientist, we had serious domain over our laboratories, but little sway in the grand scheme of things. All of us were assigned lab duties. Mine was “ethanol disbursement officer” meaning that I had the keys to jugs of pure unadulterated alcohol that could intoxicate the entire campus. George Cody’s duty was to keep track of a large liquid nitrogen cylinder at the loading dock of the Lab. Sometimes that chore kept him busier than he would have liked.

            Liquid nitrogen is used for many things in a laboratory. It’s temperature is -196°C. It will freeze just about anything. In fact, if liquid nitrogen drops remain on your skin for too long, you’ll get a nasty burn. Accordingly, dermatologists use liquid nitrogen to remove cancerous tissue and unwanted moles on skin. George used it to cool his NMR magnet and needed over 100 liters every week, usually on Friday afternoon. I used it for making chemical products of amino acids. Doug Rumble needed it for measuring oxygen isotopes in rocks.

Doug Rumble (l) and Craig Schiffries (r) using an isotope line with liquid nitrogen, circa 1992

            Filling the big cylinder outside happened via a delivery truck about every 4-5 weeks and was quite expensive. Not only was there a definite need to have liquid nitrogen on hand at all times for science, but there was a cost issue as well. Users were asked to fill out a simple signup sheet posted by the door. Often folks forgot. In the winter of 2004-2005, there were several times in which the big cylinder was somehow left open, bleeding the precious liquid into thin air, leaving the cylinder completely empty. No one would admit to leaving open a valve or forgetting to shut off the main tank. Although no person admitted to a mistake, people began to talk about seeing a raccoon in the area, thinking that just possibly….

            In response to Lab hallway theories and discussions, I penned a “Nancy Drew” story with the names of Carnegie people thinly disguised. For those of you who have never heard of Nancy Drew (https://en.wikipedia.org/wiki/Nancy_Drew), she was a young gal who often solved mysteries that her police chief dad struggled with. In my day (1960s), all girls in middle school (10-13 years old) read Nancy Drew books. Some reacted to my story that I had the mentality and sense of humor of a high school student. Younger folks on campus thought that I was pretty bad ass. If I could have figured out how to put that on my CV, I would have.

            Below is my first Nancy Drew story. Not anywhere near the Great American Novel, but a start.

-------- Forwarded Message --------

Subject:	[Everyone] Special Notice for Alert Scientists
Date:	Wed, 26 Jan 2005 13:18:23 -0500 (EST)
From:	Marilyn Fogel <m.fogel@gl.ciw.edu>
Reply-To:	m.fogel@gl.ciw.edu
To:	everyone@gl.ciw.edu
CC:	everyone@dtm.ciw.edu

The Mystery of the Disappearing Nitrogen

by Nancy Drew

Nancy was drinking a glass of whole milk after school one afternoon, when

her father, Chief Inspector Albert Drew, came home, threw his brief case

on the floor and bellowed out a loud, "Dagnab it!" Nancy jumped almost a

foot off of her chair, because her normally serious and competent father

had almost never (but not quite) used a swear word.

"Gee Dad, what's up? Can I help?"

"Its the most puzzling case I've ever had to deal with. There were clues

everywhere, and now this!" he answered her. Nancy took a sip of milk,

offered the Old Man a cookie, and waited for him to continue.

"At first," he said, "I was certain we had a simple open and shut valve

case with the liquid nitrogen tank. It was certainly nothing a little

common sense and good old gum shoe work could solve. But this afternoon

the case was blown wide open by the most disturbing news."

Nancy nodded, drank more milk, and offered him another cookie.

Bolstered with sugar and chocolate, he continued, " The tip came in this

morning and I just can't believe it yet. My head is blowing off steam like

a leaking nitrogen tank. I was snooping around the gas cylinders, poking

my head in the dumpster, and looking at the tell tale patterns of 4 liter

nitrogen dewars in the snow, when I first saw it."

Nancy poured another glass of milk, this time adding a shot of brandy

while her father was deep in thought. She offered him some brandy to go with his third cookie.

"There high in a tree next to the liquid nitrogen tank was the fattest

raccoon I have ever seen, and I can tell you that while I've been on the

force, I've seen a lot fat ones waddling through vacant alleyways. But

this one was different! He had a Huge Grin and suddenly starting talking

to me. I noticed that he was holding a hose made of braided stainless

steel and he was inhaling deeply."

Nancy got a clean glass from the sparkling cabinets in her mom's clean

kitchen and filled it with brandy laced with a bit of tequila. For the

Inspector, she topped off his glass with tequila this time, hoping it

would not ignite as he lit his pipe.

The Chief went on. "As I stared at the Raccoon, he started talking to me.

Then, I started answering him and even went on to ask him some questions.

Before you knew it, I was deep in conversation with him. Without much

prodding he admitted that he was the culprit responsible for the liquid

nitrogen losses over the weekend and Monday night. Imagine that! Not

only was this raccoon capable of filling up a dewar (and presumably then

inhaling it), he was also mischievious enough to do it twice. I thought it

was the biggest break in my career, when suddenly the raccoon dissolved in

front of my very eyes."

He downed his tequila, wiped his mouth, and drank staight from the bottle

this time. Nancy poured herself a shot, salted her hand, and tipped her

head back to deliver the tequila straight home.

Inspector Drew drew himself up to his full, incredible height, his crewcut

trimmed and waxed just so, his shoes polished and brilliant, before

admitting the last piece of information that would trouble the family for

a long time. "All that was left of him was his big shining smile. I used

my cell phone to take a picture of that smile, but guess what? Blank,

nothing there. I slapped myself a couple of times, fired off a few rounds

of my service revolver, and looked again. There they were. Tracks. Raccoon

tracks in the snow. I heard the laughing of that raccoon as the gas valve

opened again as I watched it."

Draining the remaining tequila in the bottle and sitting down finally. He

blurted out what he was afraid of from the start. "Nancy, I am convinced

that Raccoon was no ordinary urban animal seeking food. I believe he came

straight from Titan, the distant methane moon. He must have needed to

breathe pure nitrogen because all organisms on that planetary body are

anaerobes, shunning oxygen."

"Daddy!' Nancy squeeled, delirious with the news. "You've found

Extraterrestrial Life!" just before she and the Inspector passed out at

the kitchen table.

Stay tuned for Chapter Two.

To be continued.

Meteorites from out of this world

Steelie (left) and George Cody (right), Japan 2008

         As an isotope biogeochemist with a fully working laboratory, I am often included in studies far outside of my range of expertise because I can make reliable and precise analyses of organic materials. Fortunately, at the Geophysical Laboratory this happened frequently! Collaborating on a diversity of scientific projects is one of the most satisfying and challenging aspects of my chosen field. My interest in carbonaceous chondrites started when staff scientist George Cody began collaborating with Carnegie’s Department of Terrestrial Magnetism staff member, Conel Alexander. George, an organic geochemist who specializes in the analysis of complex organic matter, is an expert at using solid-state NMR to interrogate the structure kerogen and coal. He’s also developed a unique talent for using a special type of X-rays, XAFS (X-ray Absorption Fine Structure), to learn intimate details about the chemical bonds in geochemical materials. It was a natural extension of this work that he applied his analytical skills to the study of meteoritic organic matter. Conel, a cosmochemist, has an encyclopedic knowledge of carbonaceous meteorites and a knack for obtaining significant quantities of rare meteorites for destructive analysis.

         In 2002, George and his colleagues examined the molecular structure of the insoluble organic matter (IOM) by NMR spectroscopy. Then, Conel took the lead on purifying IOM from a great variety of chondrites. We were off and running with isotope studies. Over time, I gained a real appreciation for this kind of work for the following reasons. After studying terrestrial organic matter of all ages, meteoritic IOM was the perfect medium for understanding almost everything about isotope effects that are catalyzed by nonbiological reactions. IOM could be formed under high temperature conditions; it could be heavily metamorphosed; it could have been formed at ultra-low temperatures; or a combination of all these could be responsible. Although the soluble organic compounds in meteorites could readily include contamination from Earth, the IOM phase did not.

George Cody with colleagues at the Beamline

         Our first study (Alexander et al., 2007) with 75 different meteorites measured the amount of organic carbon. It ranged from 0.002% to slightly >2% of the meteorite. At a first glance, we could tell we were dealing with a great diversity in synthesis and molecular structure. Conel had hoped we’d have a diversity in IOM chemical composition based on his informed choice of so many different meteorites types. The carbon isotope signals in IOM varied with just about the full range of bulk organic carbon found in Earth materials. Although the carbon isotope compositions of specific compounds in meteorites (e.g., Murchison; Engel et al., 1990) have values that are anomalously enriched in the heavy isotope of carbon (¹³C), bulk meteoritic IOM did not. Our study was the first study to include a diversity of meteorite types and weathering conditions.

         The hydrogen isotope values were spectacular: up to 5% heavy hydrogen (²H) relative to 156 parts per million ²H found for most of earth’s materials. For me, the challenge of making measurements with such a huge ²H signal was very instructive. We learned about “blanks” and “memory” especially with the meteorites that had such ²H enriched isotope values. Conel and I developed a suite of reference materials with isotopic compositions of 1%, 2%, and 3% ²H that we carefully weighed and analyzed with each batch. After every isotopically heavy measurement, we ran a “blank” that was typically too small to capture, but cleared the slight “memory” from the previous sample.

         Our analyses included meteorites from many classes that have names that don’t make any sense to me, but are loved by those who study meteorites full time. Meteoritists assume that each type of meteorite comes from a single parent body formed from a uniform reservoir in the solar nebula. This may not be the case. We measured an extreme range in the isotopic and elemental compositions within one meteorite class alone, which means that there are different processes taking place during the formation of IOM in parent bodies. Our results could not predict whether the IOM was formed in the solar system or an interstellar location.

         For a biogeochemist, this means that within a solar nebula, there are different abundances of volatile gases. The isotopic compositions, therefore, could represent the formation of IOM at different stages of the formation and reaction in the nebula.  We concluded the following: “Taken together, the presence of large isotopic anomalies in the IOM and the higher abundance of IOM-like material in comets compared to chondrites require that if IOM is solar it formed in the outer rather than the inner Solar System (Alexander et al., 2007).” It still humbles me today to analyze material that could have originated from outside our solar system.

         One of our findings contributed significantly to the ongoing controversy about the source of water to the terrestrial planets (Alexander et al., 2012). Previously, it had been thought that water-rich comets delivered water as the planet passed through cometary tails. We proposed that meteorites and their parent asteroid bodies, rather than comets, were the primary source of planetary water. After analyzing the IOM hydrogen isotope compositions, we backtracked and compared that data to the hydrogen isotopes in bulk, whole-rock meteorites. Our results showed that Earth’s water was closer in isotopic composition to the water in chondrites than it was to the water in comets. Further, we concluded that the chondrites originated from the region of the solar system between Mars and Jupiter and came from a variety of different parent bodies.

         The third meteorite endeavor I worked on began with Andrew Steele. He had shifted his career from microbiology to planetary sciences after working at NASA’s Johnson Space Flight Center and developing expertise on the AMASE expeditions. Steele pioneered the use of a specialized instrument (WiTek Raman) for examining the relationship of macromolecular carbon with minerals on a nano to micro scale. While his work on the Martian meteorite ALH 84001 showed that organic carbon molecules are indeed indigenous, it was a “one off”.  Steelie wanted to learn if what he found in that meteorite could be found in others from Mars. Mars sample return missions, originally scheduled for 2005, then 2008, then not at all, were going to provide material for all of us to examine with sophisticated lab instrumentation. Our Geophysical Laboratory stable isotope lab was prepared and equipped to handle C, N, H, S, and O isotopes in all types of organic and inorganic phases, if we had the chance to get our hands on returned samples.

         Instead of returned martian rocks, Steele obtained 12 known martian meteorites. I began work with Roxane Bowden, our isotope Lab Manager, to measure %C and the isotopic composition of very small quantities of powdered “Martians” that Steele passed to us as though they were precious gems.

         Roxane started as a lab manager for me when I went to NSF in 2009 as a rotating program director. I posted an advertisement on Isogeochem (the listserve for isotope geochemists like me) and within 30 minutes I received a reply from her. Turns out her husband, now a Colonel in the US Army was posted to Walter Reed Hospital. She was living in Silver Spring, Maryland, and looking for a job. Roxane had over 10 years of experience working in Kansas, North Carolina, with a Ph.D. from Canada. She visited the lab a couple of days later.

Weifu Guo, Dominic Papineau, Marilyn, Roxane, Derek Smith (left to right) and Elementar Engineers 2011

         At that time we had an instrument—the high temperature TC/EA—on the frizz. I had it apart and was examining it. I asked Roxane to have a look as well, and she received a nasty electrical shock! Oops. She survived without any problem, and accepted the position. Roxane kept a strict lab—no fooling around, no short cuts, and her work was always first rate, even if a bit “slow” for the younger postdocs who were anxious to get their data completed. Roxane mastered the elemental analyzers (two of them), the TC/EA, and the GasBench. She also figured out how to measure unusual sulfur isotopes using the Elementar CUBE—a beast that was oversold on its capabilities. One summer, we managed to get her to Svalbard where she walked on glaciers and saw the camaraderie we enjoyed with AMASE.         

Roxane Bowden, Marilyn, and Steve Squyres, Svalbard 2009

         Together, she and I developed a protocol that was enforced by Roxane’s strict adherence to quality control. Anything that touched the samples was muffled in a furnace at 500°C for two hours. All utensils were rinsed with distilled, deionized water, because even an alcohol wash leaves a carbon residue. The elemental analyzer autosampler was cleaned, the combustion and reduction columns were renewed, and the mass spectrometer was checked out with blanks, boat blanks, and procedure blanks. This ensured that we were able to reliably measure carbon isotopes in less than 1 microgram of carbon. This is quite a feat. It is extremely difficult to control contamination from air, surfaces, and natural exposure. Such stringent measures are needed because most meteorites are found many years after they came to Earth (e.g. ALH 84001), exposing them to colonization by microbes or contamination by organic matter in soil or dust.

         To determine the carbon isotope values of indigenous martian carbon, we subjected each sample to a series of analyses. Our first included all carbon: both inorganic and organic. We assumed that a meteorite might have picked up terrestrial carbon. The second step was combustion in air at 550°C, which removed all simple carbon molecules like oils or amino acids, and left high-molecular weight organic carbon. Then we acidified the sample to remove inorganic carbonate and measured values again to give us total martian organic carbon (TOC). We found only very small amounts--0.0019 to 0.0095% with only a half a microgram of carbon or less in the sample. The carbon isotope values overlapped with terrestrial carbon. We were able to pick out discrete minerals, olivine crystals, from the meteorite DAG 476 to compare with the bulk meteorite and showed that the carbon was indeed indigenous to the martian meteorite.

         How did it form? Was this a product of a living organism? Together with Steele’s microscopic investigations, we assembled a pathway for organic carbon synthesis on Mars. The carbon was found in association with high temperature mineral phases in 11 out of 12 martian basaltic rocks. Based on the location next to these minerals, we concluded that the organic carbon precipitated from reduced carbon phases inside melted minerals phases hosted by olivine (Steele et al., 2012). This carbon, formed by igneous processes, was detected in meteorites that covered most of martian geologic history from 4.2 billion to 190 million years ago. We concluded that the organic carbon found on Mars should not automatically be considered to be the result of extraterrestrial biological activity.

         For the decade or more that I worked on meteorites it impressed me how precious these exceedingly rare samples are and what a boon for planetary scientists to have them in their hands. Each year, NASA selects a team of scientists to travel to Antarctica to search for meteorites that might have fallen in previous years. Dark rocks on icy, white surfaces will melt the snow around them making them easy to see. The other major source of meteorites is from the Sahara desert, where alternatively, there is little to no vegetation to obscure the meteorite falls. NASA’s strategy of funding the study of cosmochemistry with samples in hand (meteorites), as well as through complex and expensive missions, has advanced our knowledge about the solar system to a remarkable degree in the past few decades. Given what we know now about organic carbon on Mars, in the coming 10 to 20 years the question of whether life arose elsewhere in the universe, I believe, will be answered.