by Charles Baum
Earth may have reduced the quantity of organic molecules, but at the
same time they increased the diversity of complex prebiotic chemical
species.
MOLECULES FROM HOT ROCKS
Of all scenarios for the prebiotic production of organic molecules,
none is more original (and correspondingly controversial) than the
idea of Friedemann Freund, a longtime researcher at the NASA Ames
Research Center. He claims that igneous rocks were, and still are, a
principal source of Earth’s organic molecules. “Maybe,” he remarked
to Wes Huntress, the Geophysical Lab’s director, “the next chapter in
the origin of life is written in the solid state—in the dense, hard, seem-
ingly hostile matrix of crystals.”
Freund, who is as persistent and unflappable as anyone you’re ever
PRODUCTIVE ENVIRONMENTS
125
likely to meet, smiles and quietly presents his case. Tall, lean, with a
shock of graying hair, he speaks gently, with a slight German accent
and lots of eye contact. He’s always ready to talk about what he’s doing
and seldom expresses the slightest doubt that he’s onto something
important.
Here’s how he claims it happens. At high temperatures, every melt
contains some dissolved impurities. Molten rocks are no exception;
they always incorporate a little bit of water, carbon dioxide, and nitro-
gen. As the melt cools, minerals begin to crystallize one after another.
The first mineral might be rich in magnesium, silicon, and oxygen, but
inevitably it will also incorporate a small amount of carbon and nitro-
gen—elements that don’t easily enter the crystal lattice. These residual
elements concentrate along crystal defects—zipperlike elongated
spaces where the foreign atoms can react and, according to Freund,
ultimately form chainlike molecules with a carbon backbone. Freund
suspects that every igneous rock has the potential to manufacture such
organic molecules. When the rocks weather away, so the story goes,
they release vast amounts of organic carbon into the environment.
Many scientists would say that’s a wacky idea. “I am a hundred
percent sure that the Freund paper is utter nonsense,” asserts Washing-
ton University mineralogist Anne Hofmeister. “Most igneous rocks
form from an incandescent melt at temperatures greater than
1,000°C—temperatures at which even the hardiest organic molecule is
fragmented into carbon dioxide and water. By contrast, organic con-
tamination is everywhere in our environment.” What causes Freund’s
observed organics? “It’s surface residues,” Hofmeister says, “probably
sorbed out of the air.”
Freund rests his case on two sets of samples he has been studying
for almost a quarter century. Two-inch-long synthetic magnesium ox-
ide (MgO) crystals, produced by cooling a white-hot MgO melt from
2,860°C, serve as a simple model system. Pure MgO should be clear
and colorless, but Freund’s crystals have a cloudy, turbid interior, sug-
gestive of pervasive impurities. Infrared spectra reveal the sharp ab-
sorption features of carbon-hydrogen and oxygen-hydrogen bonding,
both characteristic of organic molecules. Studies of the crystals’ un-
usually high electrical conductivity and other anomalous properties
have further convinced him that the supposed MgO crystals are loaded
with excess carbon and hydrogen. The clincher: Subsequent analyses
of molecules extracted from crushed MgO crystals reveal the presence
126
GENESIS
of carboxylic acids, which just happen to be essential molecules in the
metabolism of all cells.
Studies of natural gem-quality olivine, an attractive green mineral
that is among the commonest constituents of igneous rocks, comple-
ment Freund’s work on synthetic MgO. Once again, his spectroscopic
studies revealed C–H and O–H bonds; once again, he extracted or-
ganic molecules from crushed powders. Olivine crystals hold an as-
tonishing 100 parts per million carbon, he claims. Furthermore, much
of that carbon occurs in biologically interesting, chainlike organic
molecules.
Others remain unconvinced. Caltech mineralogist George
Rossman duplicated some of Freund’s olivine results with dirty crys-
tals. “I ran a sample of ours that had been standing around for a while,”
he told Anne Hofmeister in 2002. “It had the organic bands. I washed it
off with organic solvent and re-ran it. No organic bands.” Organic con-
tamination is everywhere, so any surface—especially any powder—no
matter how well cleaned, will quickly become loaded with adsorbed
organic molecules. Freund counters that the types of molecules he ex-
tracts, carboxylic acids, are not typical of any ordinary environmental
contamination. They must have come from inside the mineral.
Freund had won relatively few converts by the summer of 2003,
when he came to George Cody’s lab to duplicate his extraction of mol-
ecules from olivine. For several weeks, a white-coated Freund was an
amiable fixture at Cody’s lab bench. He meticulously washed and pow-
dered the semiprecious stones, extracted carbon compounds with
strong solvents, and analyzed the samples with Cody’s battery of high-
tech instruments. Sure enough, every crystal seemed to release a small
hoard of carbon-rich molecules. There wasn’t much, certainly, but the
volume of igneous rock that has formed and eroded over the course of
geological history is immense. So, by Freund’s estimates, solid rocks
have provided one of Earth’s largest and most continuous sources for
the emergence of biomolecules.
Scientific progress involves a long process of hypothesis and test-
ing, bold claims, and critical counterarguments. Not surprisingly,
Freund’s hypothesis has received a lot of scrutiny and not a little dis-
dain. But those unexplained carboxylic acids can’t be ignored. And so,
for the time being, the jury is still out.
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127
THE MULTIPLE-SOURCE HYPOTHESIS
Where did life’s crucial molecules form? In spite of the polarizing ad-
vocacy of one favored environment or another by this group and that,
experiments increasingly point to the possibility that there was no
single dominant source.
It’s not a matter of Millerites versus ventists, or deep space versus
Earth’s surface. Many ancient environments boasted carbon atoms and
sufficient energy to initiate their chemical transformations. Many
environments must have contributed to the prebiotic inventory.
Lightning-sparked gases were a major source, to be sure, as were UV-
triggered reactions high in the atmosphere. Deep in the ocean, in en-
vironments ranging from lukewarm to boiling hot, molecules must
have been made in abundance, as they certainly were within some re-
active rocks of the crust (and, if Tom Gold is correct, perhaps in the
much deeper mantle). A wealth of organic products also rained down
from space, formed in remote dense molecular clouds and concen-
trated i
n the carbon-rich meteorites and asteroids that coalesced to
make our planet.
The bottom line is that the prebiotic Earth had an embarrassment
of organic riches derived from many likely sources. Carbon-rich mol-
ecules emerge from every conceivable environment. Amino acids, sug-
ars, hydrocarbons, bases—all the key molecular species are there.
So the real challenge turns out to be not so much the making of
molecules, but the selection of just the right ones and their assembly
into the useful structures we call macromolecules. That process re-
quired a higher level of emergence.
Interlude—Mythos Versus Logos
People of the past . . . evolved two ways of thinking,
speaking, and acquiring knowledge, which scholars
have called mythos and logos. Both were essential.
Karen Armstrong, The Battle for God, 2000
“Whoa, wait a minute!” My wife, Margee, sets aside my
draft, her expression a cross between confusion and ex-
asperation. “Is any of this stuff true? Who’s to say you’re not just
writing another creation myth?”
“What do you mean? This is science.” How could she miss
the point? “There’s a big difference between myth and science!”
“But you’re just making up a story. It’s really ancient history—
no one will ever know for sure how life started.” She’s warming
up to the debate. “Besides, you’re constantly saying ‘We don’t
know’ and ‘The jury’s still out.’ Can you be sure about anything?”
“Gimme a break!” was about the cleverest comeback I could
think of, as I turned back to the word processor.
So which is this book? Logos? Mythos? Some combination of the
two? Am I writing the truth, or only just-so stories?
The distinction is not always clear-cut. The studies of life’s
origin are in some ways like the efforts of archaeologists to docu-
ment the history of ancient Troy. Troy fell to the Greeks in about
1190 BCE and eventually was buried under the litter of later cit-
ies. Real people were born, led their lives, and died in Troy; nev-
ertheless, most of that rich, poignant history is lost forever. We
learn fragments of the truth from excavations, artifacts, and an-
cient documents. But mythology always lurks in the background.
The Iliad, the Odyssey, and the Aeneid inevitably color our un-
derstanding of the great city’s past.
129
130
GENESIS
Life, too, emerged through some real process. Molecules
formed, they combined, they began to replicate. Much of that
history is also lost forever. We will never know exactly where or
when the first living entity arose, nor is it likely that every chemi-
cal detail of the process will ever be known for certain. Scientists
flesh out the process with their own favorite origin stories: Miller’s
primordial soup, Gold’s deep hot biosphere, Wächtershäuser’s
sulfide surfaces. We tend to favor the stories told by our friends or
our mentors, while discounting those of our rivals. And even if we
do succeed in making life in the lab, there’s no guarantee that
that’s exactly the way it happened 4 billion years ago.
Nevertheless, science and myth differ in a fundamental way.
Scientific stories must win support through logically sound theory,
rigorously reproducible lab experiments, and independently veri-
fiable observations of nature. A scientific hypothesis must make
unambiguous predictions. If those predictions fail, the story is
deemed false by the scientific community and is cast aside. Today
we may debate the details of the process, but all scientists agree
that there must be a true origin-of-life story. That truth is our com-
mon goal.
There’s so much we don’t know and, as you have undoubt-
edly noticed, much of this book is qualified with phrases of un-
certainty. Hardly an experiment or theory goes unchallenged, and
groups of researchers often reach diametrically opposed conclu-
sions. But we have attained a vibrant stage in origins research,
one in which we are increasingly aware of what we don’t know
and, consequently, are increasingly focused on what we must
learn. A sustained, confident international program of research
has supplanted the naïve optimism of the 1950s and 1960s. And
so the scientific stories come thick and fast as theory, experiment,
and observation winnow the universe of possibilities.
Part III
The Emergence of Macromolecules
The beginning and end points of life’s emergence on Earth seem
reasonably well established. At the beginning, more than 4 billion
years ago, life’s simplest molecular building blocks—amino acids, sug-
ars, hydrocarbons, and more—emerged inexorably through facile
chemical reactions in numerous prebiotic environments, from deep
space to the deep crust. A half-century of compelling synthesis research
has amplified Stanley Miller’s breakthrough experiments. Potential
biomolecules must have littered the ancient Earth.
The end point of life’s chemical origin was the emergence of the
simple, encapsulated precursors to modern microbial life, with all of
life’s essential traits: the ability to grow, to reproduce, and to evolve.
Top-down studies of the fossil record hint that such cellular life was
firmly established almost 4 billion years ago.
The great mystery of life’s origin lies in the huge gap between mol-
ecules and cells. Ancient Earth boasted oceans of promising biomol-
ecules but, like a pile of bricks and lumber at a building supplier, more
than a little assembly was required to achieve a useful structure. Life
requires the organization of just the right combination of small mol-
ecules into much larger collections—macromolecules with specific
functions. Making macromolecules from lots of little molecules may
sound straightforward, but what most books don’t mention is that for
every potentially useful small molecule in that prebiotic environment,
there were dozens of other molecular species with no obvious role in
modern biology. Life as we know it is incredibly picky about its build-
ing blocks; the vast majority of carbon-based molecules synthesized in
prebiotic processes have no obvious biological use whatsoever. That’s
why, in laboratories around the world, many origins researchers have
shifted their focus to the emergent steps by which just the right mol-
ecules might have been selected, concentrated, and organized into the
essential structures of life.
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10
The Macromolecules of Life
To purify and characterize thoroughly all [biomolecules]
would be an insuperable task were it not for the fact that
each class of macromolecules . . . is composed of a small,
common set of monomeric units.
Lehninger et al., Principles of Biochemistry, 1993
We are chemical beings. Every living organism, from the simplest
microbes to multicellular fungi, plants, and animals, incorpo-
rates thousands of intricate molecular components
. All of nature’s di-
verse life-forms grow, develop, reproduce, and respond to changes in
their external environment—vital tasks that must be accomplished by
exquisitely balanced cascades of chemical reactions.
The more biologists learn about life, even the most “primitive”
single-celled organisms, the more amazingly complex life seems to be.
Everywhere you look, living entities have found their niche, and they
survive in wonderfully varied ways. Indeed, in a sense, chemical com-
plexity seems synonymous with life. Yet emergent systems, however
complex, are usually built from relatively simple parts, and life is no
exception.
One of the transforming discoveries of biology is that all known
life-forms rely on only a few basic types of chemical reactions, and
these reactions produce a mere handful of molecular building blocks.
Virtually all of life’s essential construction materials are carbon-based
organic molecules that combine by the thousands to form layered en-
closures or chainlike polymers. In every instance, just a few kinds of
small molecules assemble into a great variety of larger structures.
In the early nineteenth century, conventional wisdom held that
life’s chemical compounds formed by their own mysterious rules, per-
haps governed by a “vital force.” Many scholars assumed that the na-
133
134
GENESIS
scent science of chemistry applied only to the inorganic world—the
world of rocks, minerals, and metals. This perception changed in 1828,
when the young German chemist, mineral collector, and gynecologist
Friedrich Wöhler demonstrated that biological molecules are no dif-
ferent in principle from other chemicals. He combined the common
laboratory reagent cyanic acid with ammonia and succeeded in pro-
ducing urea, which is extracted in the kidneys and found in urine.
Wöhler’s letter announcing his important discovery displayed a sense
of whimsy not always associated with German academicians: “I can no
longer, as it were, hold back my chemical urine: and I have to let out
that I can make urea without needing a kidney, whether of man or
dog.” By employing straightforward lab techniques to produce a chemi-
cal substance known only from life, Wöhler convinced his colleagues
of the ordinariness of organic chemistry.