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| Two of my astrobiology colleagues: Andrew Steele (l) and Steve Shirey (r), Carnegie 2012 |
“The
probability for the chance of formation of the smallest, simplest form of
living organism known is 1 to 10,340,000,000.... The size of this figure is
truly staggering, since there are only supposed to be approximately 1080 electrons
in the whole universe!” Harold Morowitz, in Energy Flow in Biology (1968).
In 1996, NASA announced that it had
found evidence of life contained in the Martian meteorite Alan Hills 84001
(McKay et al., 1996). They held press conferences and presented evidence for
what they termed bacterial cell structures in the meteorites, along with some
amino acid profiles. News spread like wildfire among Mars aficionados and
skeptics alike. The search for life on Mars stimulated several lander and
orbital missions to Mars. At the same time, NASA under the advice of Wesley T.
Huntress, Associate Administrator for Space Science, had the idea to form the
NASA Astrobiology Institute (NAI), a virtual institute in which scientists in
disciplines as far-ranging as astronomy and astrophysics would regularly engage
with molecular biologists and geochemists. Objectives central to this effort
were to understand how life arose on planet Earth, to determine when it arose,
and to devise a set of criteria everyone could agree on that constituted
evidence of life.
This task has been more difficult than
it sounds. To this day, NASA and NAI scientists still are discussing how they
will determine which chemical or physical line(s) of evidence constitute proof
that there is life on another planetary body. I was part of two original NAI
teams that took very different approaches to search for life. The Jet
Propulsion Lab (JPL) team focused on biosignatures. Biosignatures are fingerprints
of life such as isotope fractionation patterns or elemental ratios. Ken
Nealson, who specifically moved from University of Wisconsin to JPL, led the
effort. Our work was carried out in both modern extreme environments as well as
in ancient rocks. Being on the JPL campus, this NAI team used several new
techniques that were being specifically designed for space flight. The goal of
this group was to develop biosignatures in tandem with new analytical methods
in the lab to help us to understand the significance of biosignatures observed
in the field.
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| (L-R) Wes Huntress, Doug Rumble, Marilyn, Ken Nealson, 2002 |
On a geological time scale of hundreds,
thousands, or millions of years, biologically-resistant material gradually
obtains an isotopic and chemical composition that has little resemblance to
original biochemical compounds. If we were to find evidence of life in martian
rocks billions of years old, we needed to broaden our thinking. Rather than
searching for pristine molecules similar to ones in living organisms, we needed
to know what these molecules would look like—their biosignature--after they had
been substantially degraded. Working with postdoc Sue Ziegler, we fed a simple
mixed culture of microorganisms a single protein, Rubisco, the protein I
studied for my PhD work. The bacteria ate the Rubisco protein completely in
about 36 hours, turning the Rubisco protein into their own bacterial proteins.
We compared the chemical isotope
biosignature of the amino acids in the Rubisco with the isotope biosignature of
the amino acids in the microbes. The biosignatures were completely different.
After the bacteria had eaten the Rubisco, some slightly larger heterotrophic
organisms ate the bacteria. Bacterial proteins were decomposed and recycled
into these larger beasts. In a very short time, hours to days, the original
Rubisco protein isotope biosignature had been altered twice. In the real world,
almost any biomass made by plants and animals is quickly metabolized by
microbes and almost never enters the fossil record. It is a reasonable
assumption that if there were living organisms on another planet, a similar
hierarchy of organisms would probably have evolved.
The approach by the Carnegie team,
which I also worked with, was completely different. Geophysical Laboratory
staff member Bob Hazen and Harold Morowitz (George Mason University) had the
idea that we might be able to study some of the most basic reactions fundamental
to all organisms. Bob Hazen is an
accomplished writer of popular science books, textbooks, and scientific
articles in his discipline. Over the years, I watched him transform from a
high-pressure mineralogist to an astrobiologist to a big picture thinker on the
nature of carbon in the deep earth. He was never a “lab guy” like the rest of
us at the Geophysical Lab. Instead, he partnered with bright people like Larry
Finger, George Cody, Robert Downs, and others to anchor the data collecting. Often,
we sparred with one another, at unpredictable times. He saw my work as
incremental, which is what most scientific advances truly are. I saw his work
as broad brush, not getting at the heart of problems. Either way, Hazen
sustained having novel scientific ideas which he supported with his
encyclopedic ability to read articles, understand them, and write about them
with style.
Harold Morowitz was a real original
thinker and intellect. Working at a second tier university in northern
Virginia, he struck me as a person who could work anywhere that welcomed
complex thoughts. Harold knew the biochemical pathways and enzymes thoroughly, which we appreciated. He visited to discuss the experiments,
and sometimes tension arose when hypotheses did not match results and findings.
Both he and Bob Hazen were scholars, while the
rest of us were soldiers in the laboratory figuring out difficult analytical
problems. Fortunately, George Cody and Harold worked on the same plane and were
able to match their talents to produce the detailed work on abiotic organic
synthesis.
Hazen and Morowitz’s idea was to use heat and
pressure—non-biological hydrothermal chemistry--rather than biological enzymes
to see if we could simulate the TCA cycle reactions. The TCA cycle (also known as
the Krebs cycle) operates generating energy for cells in just about all known
organisms. Some microbes are missing a piece of the cycle, but in general, the
TCA cycle is at the heart of metabolism. Geophysical Laboratory staff member
George Cody, former Geophysical Laboratory Director Hat Yoder and I, as well as
Bob and Harold, postdocs Mark Teece, Jay Brandes, Tim Filley, Jennifer Blank,
and Nabil Boctor, discussed how this could be carried out. Bob and his postdocs
would seal simple organic reactants into gold tubes—1/4” in diameter and about
4 inches long--that served as reaction vessels.
Then, Hat Yoder would take the gold tubes and subject them to high
temperatures (200°C) and high pressures in his laboratory’s apparatus that took
up an entire room. He was used to doing experiments at thousands of atmospheres
of pressure and at least 500°C. It was a challenge for him to reduce the
pressure and temperatures to levels that would not completely burn up the
organic starting materials. He would place the small gold tubes into larger
metal cylinders that he referred to as “bombs” because if they were made
improperly they could explode and had the power to shoot through pretty think
steel walls. Fortunately, that did not happen with any of our samples.
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| We tried to create "life" with heat and temperature, 2002 |
George and his postdocs would analyze
the products of the reaction. George Cody is one-of-a-kind, often self-absorbed
and oblivious to humans, other times thinking about the long-term vision for
the Geophysical Laboratory and his colleagues. Cody is most comfortable at the
console of his custom built NMR spectrometer. As he evolved from being a coal
chemist to an organic geochemist to an astrobiologist to a generalist, his
skills in analyzing complex data sets thoroughly distinguish his work. At
parties, George often can’t leave his work behind. After a few glasses of red
wine, he may regale his friends about hamiltonians (an obscure parameter
measured by his NMR spectrometer), while his wife looks patiently on. When we
worked together, I could always rely on George to huddle with me and figure out
gnarly lab problems, personnel issues, and weird data. Mark Teece and I were to
measure the isotopic biosignature in the products; Harold and the rest of us
would interpret the results.
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| Jay Brandes (l) and George Cody at his NMR, 2001 |
Experiments were more complicated than
we ever anticipated. Eventually, Cody and team members found a potential
reaction that jump started a modification of the biological TCA cycle. This
pathway, named the hydrothermal redox pathway, is not used in any extant
organisms but may have been the ignition point for primary metabolism during
the early evolution of living organisms. One of the keys to getting this
pathway to work at all was to choose the correct metals (for example, iron) and
their sulfide minerals as catalysts. The potentially critical catalytic role of
such metallic catalysts may be a crucial link between geochemistry and
biochemistry at the point of life’s emergence. Integrating all of this, they
discovered that they were within one reaction of demonstrating a purely geochemical
carbon fixation pathway that closely mimics the TCA pathways, but they were
unable, ever, to figure out how to do the last remaining reaction
non-biologically.
Origin of life studies were being
carried out across the NAI and internationally at this time (2000s). The RNA world
hypothesis, promoted by Jack Shostack at MIT, had been a favored pathway for
jump-starting life. RNA (ribonucleic acid, one of the molecules carrying the
genetic code) can catalyze simple reactions, directs the construction of more
complicated molecules like proteins, and holds heritable information. The
problem with this model was figuring out how to make RNA molecules in the first
place. One hypothesis was that meteorites that bombarded early Earth brought
these molecules with them.
Zita Martins and the organic
geochemists at Goddard Space Flight Center were searching for the building
blocks of DNA and RNA, nucleobases, in organic extracts of the Murchison
meteorite, one of the most famous carbonaceous chondrites of all time. Zita was
working with Danny Glavin and Jason Dworkin at Goddard, and her colleagues and
PhD advisor in the Netherlands. Using a sophisticated type of mass
spectrometry, she could detect nucleobases in some of the Murchison extracts.
She was able to zero in on these unusual and complicated structures,
essentially picking the “needles out of the haystack” of other compounds. We
began a collaboration to measure the stable isotope biosignature patterns in
these particular molecules. If they really came from outer space, these
compounds should have an isotope biosignature pattern similar to other
meteorite organic molecules. Alternatively, if these were terrestrial
contaminants, they should resemble isotope biosignature patterns of biological
molecules.
Zita arrived with extracts in hand at
the Geophysical Laboratory, and we were confident that we could readily measure
the carbon isotope patterns based on the results she measured at Goddard Space
Flight Center. Unfortunately, the analytical system I was using, a combustion-GC-IRMS
system, combusts all carbon compounds in the chromatogram, which was loaded
with a multitude of other compounds, mostly organic acids, as well as with
trace amounts of nucleobases (Martins et al., 2008).
We were able to devise a clever
analytical scheme for our instrument that separated the organic acids from the
nucleobases without any serious overlap. The carbon isotope biosignature
patterns of the organic acids had enriched levels of 13C in them,
similar to measurements others had made on these same types of compounds in
meteorites. We were thrilled when we were able to measure a 13C-enriched
carbon isotope biosignature for uracil, a component in RNA, in the Murchison
sample. The two isotope biosignatures were consistent with an extraterrestrial
origin for both compounds. We also analyzed uracil from the soil surrounding
the location in Australia where the meteorite was found. The soil uracil had an
isotope biosignature similar to terrestrial carbon—not at all like the
meteorite uracil. This work supports one of the many theories about the origins
of life. One of these theories holds that meteorites delivered organic
molecules to Earth during its formation and the period when Earth was
continually bombarded by incoming asteroids. Although it was known that amino
acids (e.g., Engel et al., 1980; Martins
et al., 2007) were common monomers in some meteorites, no one had ever found
nucleobases.
Eventually, the stable isotope
biogeochemistry studies of the Carnegie team shifted in emphasis. In phase two
of the NAI project at the Geophysical Laboratory, we began to study the
isotopic compositions of ancient sedimentary rocks and stromatolites and began
an ambitious field campaign in Svalbard, an archipelago high above the Arctic
Circle in a project termed AMASE: Arctic Mars Analogue Svalbard Expedition.
Both the NAI and AMASE endeavors required field trips to far flung places to
collect samples from ecosystems of interest to astrobiologists.
Andrew Steele AKA Steelie
With
Wes Huntress as our new Director in 1999, we began a search to hire a
replacement for Ed Hare—someone who would be a full time astrobiologist.
Carnegie and the Geophysical Laboratory hire people in very different ways than
universities. It is the sole discretion of the Director of the department to
choose and negotiate with a new staff member. For the astrobiology position, we
advertised widely and received a number of applications from interesting,
qualified individuals. A short list was struck and about five people each spent
a couple of days visiting the campus, giving a seminar, and trying to impress
the scientific staff.
At
the time, I was involved in using a new time-of-flight mass spectrometer to
identify unknown compounds in complex mixtures. The instrument, the Protein
Chip Reader, could measure the coupling of an antibody with its antigen very
precisely. I had heard about a young man at Johnson Space Flight Center who was
developing a similar system—except miniaturized—for flying on an upcoming Mars
mission. He also heard of what I was doing and wrote me an email asking to
visit the Laboratory. I was excited by the prospect, asked for his CV, and
invited him to come for a seminar. Unbeknownst to him, his CV was circulated to
the astrobiology hiring committee. We considered him a potentially viable
candidate. Andrew Steele was officially on our radar screen.
Andrew
was, by then, working in England, so flew over to the States the weekend before
his seminar to get adjusted to the time change. I met him briefly before his
Monday seminar, telling him, “Hey! Do you know we have a staff position open
for an Astrobiologist?” He did not. The news sent him into a bit of a panic,
because Steele is usually informal in his mannerisms, dress, and speaking style.
Apparently, he purchased a new outfit, updated his talk, and practiced it again
and again before arriving at the Lab for his “visit” early Monday morning,
which morphed into an impromptu interview. His combination of microbiology,
meteorite geochemistry, technology, and Mars science was a perfect fit for what
we were looking for. An offer quickly followed.
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| Steelie at the 9:30 Club, Washington DC |
Andrew—Steelie,
as he is known to almost everyone, looks the part of a 1990s British rocker. In
fact, he is an accomplished guitarist and composer of rock music, playing and
singing in a Takoma Park band. His light brown hair reaches to the middle of
his back, or is frequently up in a man-bun or back in a ragged ponytail.
Wearing jeans purchased at a boutique shop in London and a t-shirt with science
logos, Steelie can light up a room with his outward enthusiasm. He wears his
personality and feelings on his sleeve, however. When he’s in a bad mood, it
shows. When he’s deep in thought, he paces, looking at the ground, muttering to
himself about thermodynamics and Mars.
I
was barely 13 years old when Steelie was born in January 1965. When we traveled
to conferences, NASA meetings, and fieldwork, we looked like an unusual pair.
Once—just once—in an airport rental car lot, a stranger said to him, “Your mother is waving at you over there.”
That comment resulted in endless teasing. I was not old enough to be his
mother, but earned the nickname of “Ma.” While he liked to say he thought I was
“matronly” when he first met me, I enjoyed saying about him, “Yeah, he’s my
son, living in the basement, doesn't have a girlfriend or a job, plays on an
old Atari video game all day.” The razzing continues to this day.
Steelie
hit the ground running at the Lab and built a strong team of young postdocs and
students who adored him and his unconventional style. People came from around
the world to work with him. He set up his first lab in Ed Hare and John
Frantz’s old labs, shoehorning in autoclaves, microbial culture apparatus, DNA
identification instruments, and sophisticated microscopes. He was known for
working odd hours. I’d see him slink by my office around 11 am, backpack slung
over his shoulder, often laughing. He worked until late at night, sometimes
regaling his colleagues with emails at midnight. Steelie had never been
responsible for lab personnel before. Sometimes he loved the job, other times
he found it a bother.
Often,
he was late for lab, committee, and informal meetings that he himself had set
up. Finally one day, fed up with this, his lab group and I “decorated” his
office with thousands of Styrofoam peanuts. When he saw the mess we created he
was furious and let his lab mates know, in no uncertain terms, he was angry
with their childish behavior. I let him know that I was the mastermind of the
prank, and that if he wanted grown up behavior, he should be on time like a
professional adult. We glowered a bit, then burst out laughing. I can’t say he
completely changed his ways, but he grew more “adult like” and commanded the
respect of his peers and lab group.
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| Styroform peanut crew, Steelie's lab |
Steelie’s
first field trip was with my lab group who were investigating the effects of
chicken waste (i.e., chicken &%*t) on the ecosystem. As part of this trip,
we used seine nets to sample small fish from rivers that had been potentially
polluted by chicken waste. Steelie came dressed in shorts wearing sandals. On
his first attempt at fish seining, he lost one sandal in the mud. The remainder
of the day he wore one shoe. He’d also forgotten to bring his wallet and
drivers license, something we learned was more common than not. Consequently,
when we went out for beers at the end of the day, the waitress refused to serve
him.
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| Steelie missing his shoe, 1st field trip |
Steelie’s
next field trip was the 2003 expedition on AMASE. In Longyearbyen, he purchased
a pair of fancy red hiking boots, which gave him huge blisters when he climbed
Sverrefjell volcano for the first time. I joined the AMASE team in 2004, and by
this time, he became skilled at organizing Artic fieldwork and finding signs of
life on seemingly barren rocks. Never ever one to give up, Steelie went on to
become Chief Scientist and an accomplished Arctic explorer over the years.
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| Steelie doing science in the Arctic |
Steelie is one of my Science Brothers.
Now that we live and work thousands of miles away from each other, when we call
the other answers the phone “As I live and breathe!” I watched over his
daughter when his second child was born. He mentored my son Evan when Chris and
I moved to California. Steelie was one of the first people I told about my ALS
diagnosis. I was one of the first he told about his mother’s passing. I may be
more matronly than ever. His hair and beard are tinged with gray, but we’ve got
a firm hold on life and science.
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| Steelie and Marilyn, Merced, 2014 |
A ride on the Vomit Comet
We’ve all watched those
space movies—Sandra Bullock floating around trying to repair a space ship, her
hair twirling around her head, waving herself around the universe. It’s as fun
as it looks, which I found out in 2004 on a trip on NASA’s Vomit Comet. In
order to train astronauts for the feeling of zero gravity, NASA has a special
plane taking off from Johnson Space Flight Center near Houston, Texas. In order
to achieve zero gravity, the aircraft, a large C-130 cargo jet aircraft,
follows a parabolic flight plan going up in an arc followed by descending in a
similar arc. During the upward climb, gravity is about double Earth’s gravity;
on the downward trajectory, gravity goes to zero.
My opportunity to fly on
the Vomit Comet was made possible by working with Jake Maule, a postdoc working
with Andrew Steele. Jake, now a physician at Duke University Hospital, is a
trim, sharp-looking Brit who had dreams of joining the astronaut core. His PhD
is in medicine, so he was looking to use that training combined with an
astrobiology theme to be attractive to the very competitive NASA program for
selecting astronauts. Jake and I were both interested in immunology at that
time. I had purchased an instrument capable of making the types of measurements
that can detect complex diseases like HIV-AIDS. The instrument, an ELISA reader
(enzyme-linked immuno-sorbent assay) measures the amount and strength that
antibodies have in binding to the molecules, antigens, they are trying to
remove from harming our bodies.
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| Jake Maule, Arctic, 2005 |
Jake’s idea was to use
the ELISA reader to find out whether and how antibodies and antigens hook up
together without the benefit of gravity. He asked to borrow my instrument. I
told him, “OK, but you have to take me with you!” He thought about it briefly,
and agreed. We flew down to Johnson Space Flight Center for 2 days of training.
After a morning of lectures, we went into a space simulation chamber that was
evacuated leaving almost no air, but all was fine because we were wearing
oxygen masks. The chamber was then filled with nitrogen gas—which does not
support life—and we were asked to remove our masks. It took me only 20 seconds
to feel the effects—I was unable to count to five! My mask went right back on.
Jake and I practiced our
experiments in a lab on the ground. We planned to fly 40 cycles alternating
between zero gravity and two-times gravity (2-G) during our 3 hour flight. Each
cycle lasted 20 seconds—barely enough time to complete the manipulations
needed. The morning of our flight we were given two medications to
help—Dexedrine and scopolamine-one to keep you awake and the other to keep you
from getting airsick. Donning NASA flight suits, 15 scientists, a flight
supervisor, and the flight surgeon entered the plane. Excitedly, we set up our
experiments. Ours was inside of a newborn baby’s Isolette, a plastic box with
armholes for two people to attend to a premature infant, which kept our
supplies from floating around the aircraft.
We were seated for
takeoff, then at 10,000 feet we moved to our workstations, where our feet were
placed under straps so we wouldn’t float away. When we were about to enter
zero-G, special lights flashed on. Then, as we switched to 2-G, the flight
supervisor shouted, “Feet down! Comin’ up!” We heard that phrase more than 40
times.
The first zero-G
experience made your stomach do a flip-flop. Your hair raises up, your
equipment floats around. Wow! Then, all too soon, you feel 2-G making you twice
your body weight. A slight movement of your head and you felt nauseous, even
going so far as to cause vomiting. On the second cycle, we began the
manipulations. My skills working at sea on ships tossed around by big waves
trained me for this work. Opposite to me, Jake was turning a bit green. The
flight surgeon floated by, offered him a barf bag, wrapped it up, and then went
on to the next scientist who needed some help. I’m proud to say my stomach
remained in check.
After 40 cycles of zero
G, Jake and I unplugged and floated for the next couple of parabolas. The
feeling of weightlessness, even for 20 seconds, is something my body has never
forgotten. The ability to float in air, even fly, is something we only dream
about but never experience. The trip on the Vomit Comet let my soul soar!
Because I was a trooper
on the flight, the pilots invited me to sit in the jump seat just behind them
when we were returning to Johnson. What an eye opener! First, I saw how close we were to another
airplane and how the pilots handled that. Then, a warning light came on in the
panel of instruments on the plane’s dashboard. We were all connected via
headsets, so I could hear them discussing the meaning of the orange light.
Apparently, it had to do with the functioning of one of the two jet engines.
After we safely landed, the plane was taken into a hanger for maintenance to
figure out what was happening with that engine. Turns out that it needed to be
completely overhauled. Our 2nd flight was cancelled and the Vomit
Comet was out of commission for months.
Our experiments were
successful. We determined that antibodies and antigens had no problems working
in the absence of gravity. Although humans evolved with the benefits of a
gravitational field, our biochemical systems could adapt to spaceflight.
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