by Charles Baum
to be sure, but oil fields also contain, along with methane, an abun-
dance of helium gas—a light gas that quickly escapes into space and so
could only come from deep within the Earth. How could one reconcile
the mixing of deep helium with surface biology? Gold’s conclusion:
The organic molecules that eventually become petroleum are produced
deep underground by purely chemical processes and are then modi-
fied by the action of subsurface microbes.
In this scenario, vast sources of primordial hydrocarbons—the
major molecular components of oil—exist in Earth’s mantle. Because
they are lighter than the surrounding rocks, these hydrocarbons slowly
but surely rise toward the surface, constantly refilling petroleum reser-
voirs. In Gold’s heretical view, oil is thus a renewable resource instead
of a finite one built up over millions of years by the burial and decay of
once-living cells. In an extraordinary move, Gold first published this
novel idea as an op-ed piece in the June 8, 1977, issue of the Wall Street
Journal. An oil-hungry nation in the midst of an energy crisis took
considerable notice of the radical hypothesis.
A scientific theory is useful only if it is testable, and Gold soon
proposed a test of dramatic proportions. Gold’s oil-from-below hy-
pothesis predicts that great oil fields should arise equally in many dif-
ferent types of rock, but all known petroleum has been found in layers
of exactly the kind of sedimentary formations that would have col-
lected abundant remnants of past life. Gold countered, logically, that
petroleum geologists never look for oil anywhere but in those sedi-
mentary formations. Perhaps, he suggested, immense new oil fields
were waiting to be found in igneous and metamorphic rock.
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GENESIS
Armed with his provocative theory and a persuasive, dynamic ora-
torical style, he presented a simple (and expensive) proposal to the
Swedish State Power Board in 1983. Drill an oil well in solid granite—
the last place on Earth a petroleum geologist would look. He had tar-
geted a unique and tempting granitic mass, the Siljan Ring impact site
in central Sweden. This highly fractured granite body, formed 368 mil-
lion years ago when an asteroid shattered the crust, holds tantalizing
hints of petroleum in the form of carbon-filled cracks and flammable
methane seeps. Gold’s enticing rhetoric, amplified by increasing opti-
mism from Dala Deep Gas, the company formed to do the drilling,
lured energy-poor Swedes into spending millions of dollars on explor-
atory holes.
Seven years and $40 million later, a 6.8-kilometer-deep hole had
produced only modest amounts of oil-like hydrocarbons and methane
gas—a small enough yield for oil experts to say “I told you so,” but
large enough to convince Gold that his theory was right. Where else, he
asked, could that trace of organic molecules have come from? Never-
theless, most scientists saw the Siljan experiment as a failure, and no
one is likely to drill for oil in granite again, at least anytime soon.
The modest production of methane gas and smelly, oily sludge
from the Swedish wells inspired Gold to elaborate on his theory. Ex-
trapolating far beyond his peers, he described “the deep hot biosphere”
in several articles and a popular 1998 book of that title. The vast, deep
hydrocarbon reserves at the heart of Gold’s 1977 hypothesis provide a
wonderful food source for deep microbes, which coincidently leave
their biological overprint on the otherwise abiotic oil. In entertaining
prose, he reviewed the growing and accepted body of evidence for deep
life in many types of rock—all very reasonable stuff. Gold’s conclu-
sion: Deep microbial life, much of it nourished by upwelling hydrocar-
bons, accounts for fully half of Earth’s total biomass. Though living
cells represent a tiny fraction of Earth’s total rock mass, the volume of
rock is so vast—a few billion cubic kilometers—that it shelters astro-
nomical numbers of microbes. Inevitably, our view of life has been
skewed because these microscopic life-forms lie completely hidden
from everyday view.
In April 1998, I invited Gold to visit the Geophysical Lab and
present his ideas at our regular Monday morning seminar. Seemingly
unfazed by more than two decades of impassioned objections to his
views, he delivered a polished and forceful account of many lines of
HEAVEN OR HELL?
105
evidence that petroleum is abiotic and rises from the depths. Geology,
biology, thermodynamics, experiments on organic molecules, carbon
isotopes, observations of diamonds, and, of course, the chemical prop-
erties of petroleum itself all came into play. Knowing our special inter-
est in life’s origins, he underscored the possible role of this deep
hydrocarbon source in supplying critical molecules for prebiotic pro-
cesses. Perhaps, he posited, life arose from those deep sources of or-
ganic molecules. Throughout the entertaining lecture, he bolstered his
controversial conclusions with rhetorical flourishes more suited to a
courtroom than a scientific seminar (“the only possible explanation,”
“no question remains,” the evidence “persuades one completely,” and
the like).
I doubt that anyone was persuaded completely, but we had to ad-
mire his creativity and conviction. And Tommy Gold helped to remind
us all, once again, how much we don’t know about the interior of our
planet just a few miles beneath our feet.
HEAVEN VERSUS HELL
If so many organisms exist beyond the Sun’s radiant reach, then geo-
thermal energy, and the abundant chemically active mineral surfaces
that are synthesized in geothermal domains, must be considered as a
possible triggering power source for life. To be sure, sunlight remains
the leading contender for life’s original energy source. The vast major-
ity of known life-forms do rely, directly or indirectly, on photosynthe-
sis. In many scientific circles, a surface origin of life in a nutrient-rich
ocean, under a bright Sun, remains the seemingly unassailable conven-
tional wisdom.
But that nagging problem of macromolecular formation remains.
Most known living species depend on the Sun directly or indirectly,
but the Sun’s harsh ultraviolet radiation inhibits the emergence of the
larger multimolecular structures on which all organisms depend. Fur-
thermore, if the earliest life of almost 4 billion years ago was confined
to the sunlit surface, how did it escape the brutal, sterilizing final stages
of bombardment by asteroids and comets? As Gold said over and over
again, Earth’s surface, bathed in solar radiation and blasted by light-
ning, is the truly extreme environment.
And there’s another reason to look closely at the possibility of hy-
drothermal origins. If life is constrained to form in a sun-drenched
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GENESIS
pond or ocean surface, then Earth, and perhaps ancient Mars or Venus,
are the only possible pla
ces where life could have begun in our solar
system. If, however, living cells can emerge from deeply buried wet
zones, then life may be much more widespread than previously imag-
ined. The possibility of deep origins raises the stakes in our explora-
tion of other planets and moons.
Jupiter’s fourth largest moon, Europa, presents a particularly
promising target for exploration. According to recent observations,
Europa is covered with a veneer of ice about 10 kilometers thick, cover-
ing a deep ocean of liquid water. Hydrothermal activity on the floor of
that ocean might be an ideal environment for life-forming chemistry.
Saturn’s largest moon, Titan, is another intriguing world. Though
much colder than Earth, Titan has an organic-rich atmosphere slightly
denser than Earth’s and, like all large bodies, its own sources of inter-
nal heat energy.
The idea that life may have arisen in a deep, dark zone of volcanic
heat and sulfurous minerals flies in the face of deeply ingrained reli-
gious metaphors. To many people, the Sun represents the life-giving
warmth of heaven, while sulfurous volcanoes are the closest terrestrial
analog to hell. How could life have come from such a dark, hostile
environment?
Nature is not governed by our metaphors, however cherished they
may be. Life as we know it demands carbon-based chemicals, a water-
rich environment, and energy with which to assemble those ingredi-
ents into a self-replicating entity. Ongoing laboratory experiments that
simulate deep conditions as well as those on the surface—coupled with
observations of environments elsewhere in the solar system—will be
the ultimate arbiters of truth.
8
Under Pressure
Where is this original homestead of life? . . . a place where hot
volcanic exhalations clash with a circulating hydrothermal
water flow; a place deep down where a pyrite-forming
autocatalyst once gave, and is still giving, birth to life.
Günter Wächtershäuser, 1988
The first emergent step in life’s chemical origin, wherever it may
have occurred, must have been the synthesis of organic molecules.
Stanley Miller’s experiments amply demonstrated one potential an-
cient energy source with which to effect this synthesis—lightning near
the ocean–atmosphere interface. Subsequent workers, notably Thomas
Gold, postulated deeper origins and chemically derived energy sources.
Any plausible source of carbon-based molecules should be fair game
for origin researchers. Every plausible source deserves rigorous study.
In 1996, when George Cody, Hat Yoder, and I began our research
on hydrothermal chemistry and the origins of life, we were novices in
the origins game, too naïve to suspect that we were wasting our time.
We thought that our experimental studies of organic synthesis in hot,
high-pressure water provided compelling evidence that hydrothermal
zones could have played a role in the prebiotic production of life’s mol-
ecules. Stanley Miller and his students, most notably chemist Jeffrey
Bada at the Scripps Institution of Oceanography, would have been
happy to set us straight, but we had yet to cross paths with them.
Harold Morowitz, whose ideas instigated the research, had warned us
that we might meet with some criticism. He was right.
It must have seemed odd to the scientific community that a group
of geologists and geophysicists was studying the origin of life. For al-
107
108
GENESIS
most a century, our home base, the Carnegie Institution’s Geophysical
Laboratory, had supported research on the physics and chemistry of
Earth materials at extreme temperatures and pressures. Carnegie sci-
entists had melted granite, synthesized basalt, and heated and squeezed
just about every known rock-forming mineral to understand how our
dynamic planet works. They routinely achieved temperatures of thou-
sands of degrees and pressures of millions of atmospheres—extreme
environments that would seem to have little to do with life’s delicate
chemistry. Nevertheless, the lab’s arsenal of furnaces and pressure ves-
sels stood ready to heat and squeeze almost any sort of sample, and
experiments on carbon compounds weren’t intrinsically different from
any other chemical we might have chosen to study.
EXPERIMENTS
Now, more than 2,000 experiments later, our hydrothermal organic-
synthesis program is expanded, well funded by NASA, and going
strong. Our simple strategy, much in the spirit of Stanley Miller’s origi-
nal experiments, has been to subject plausible prebiotic chemical mixes
of water, carbon dioxide, and minerals to a controlled environment—
in our case, a high-pressure and high-temperature environment typi-
cal of deep-ocean hydrothermal systems—still often employing the
classic gold-tube protocol described in the Prologue.
Our first experiments (the ones with pyruvate and carbon diox-
ide) were exhilarating. In that series we synthesized sugars, alcohols,
and a host of larger molecules, many incorporating dozens of carbon
atoms. Under extreme hydrothermal conditions, the pyruvate mol-
ecules polymerize; in some cases they form rings and branching struc-
tures reminiscent of molecules found in modern cells.
In a later set of experiments, we sealed water, nitrogen gas, and
powdered minerals into the gold tubes—a reasonable proxy for primi-
tive conditions at some hydrothermal vents. In these experiments, we
produced ammonia, an essential starting material for synthesizing
amino acids and other biomolecules. Our work suggests that hydro-
thermal vents may have been one of the principal sources of the early
Earth’s ammonia. Carrying on with this line of experiments, we put
ammonia into a capsule with pyruvate and found that these two com-
pounds react to form the amino acid alanine. By 1999, we had estab-
UNDER PRESSURE
109
lished one plausible chemical pathway leading from simple carbon
compounds, nitrogen gas, and common minerals to key biomolecules.
In 1997, shortly after our initial exciting results, Cody, Yoder, and I
submitted our first papers for peer review. We believed optimistically
that our demonstrations of facile hydrothermal organic synthesis
would be welcomed as a logical extension of the Miller–Urey approach.
After all, we, like Miller a half-century before, had subjected a closed
vessel containing water and simple carbon-containing molecules to
heat. We had followed Miller’s lead in attempting to simulate a plau-
sible prebiotic environment. And we, too, had found an abundance of
synthetic organic molecules. We thought the Miller camp might actu-
ally welcome our contribution. Boy, were we wrong!
Miller and his scientific cohort had staked their claim to a surface
origin of life, and they seemed determined to systematically head off
dissenting opinions. Their reasons were straightforward and clearly ar-
gued. While organic synthesis may occur near the 100°C limit of liquid
ments, the biomolecules of interest, notably amino acids, decompose
at a higher rate than they can be manufactured. Hydrothermal zones
on the early Earth would have destroyed many essential biomolecules
in the prebiotic ocean much faster than they could have been replen-
ished. Such hostile zones were antithetical to life. We weren’t the first
researchers to suffer these criticisms: The Oregon State group who first
outlined the hypothesis of a hydrothermal origin of life following deep-
sea discoveries in Alvin had found themselves repeatedly thwarted by
this argument, their manuscript rejected time and again. However, we
were not about to follow their example by publishing in obscure con-
ference proceedings.
Stanley Miller had been relentless in his offensive ever since the
hydrothermal-origins idea arose. In a 1988 article in Nature, Miller
and Jeffrey Bada wrote, “This proposal is based on a number of misun-
derstandings concerning the organic chemistry involved. . . . The high
temperatures in the vents would not allow synthesis of organic com-
pounds, but would decompose them.” Miller was more blunt in a Dis-
cover feature in 1992, when he called the vent hypothesis “a real loser.”
In The Spark of Life, their popular book on origin theories, Bada
and Christopher Wills dubbed those of us working on the hydrother-
mal hypothesis “ventists,” making us sound a little like the members of
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GENESIS
some fanatical religious cult. Their presentation is engaging and gen-
erally accurate, but like an argumentative rondo the old refrain ap-
pears again and again: “Vents are more likely to destroy organic
compounds than create them.” “This high temperature rapidly destroys
organic compounds rather than synthesizing them.” “At these high
temperatures, amino acids undergo total decomposition on a time
scale of only a few minutes.” “Vents . . . do terrible things to the primor-
dial soup.” Piled onto this catchy litany were other criticisms: Our start-
ing solutions were much too concentrated, the resulting products were
much too dilute, and our geological assumptions about vent-water cir-
culation were incorrect.
Our immediate reaction to the assault was defensive and angry.