by Charles Baum
goo that oozed out of our gold capsules held self-organizing molecules.
That might be worth investigating, because we had started with a core
metabolic molecule. It would be newsworthy if there were a facile path
from primitive metabolism to membranes.
On hearing my story, Dave immediately invited me to his specially
equipped lab at UC Santa Cruz (where he had moved in 1994) to try
the experiment. The following winter, I prepared some new pyruvate-
plus-water capsules and subjected each of them to two hours at 2,000
atmospheres and 250°C. I brought them, unopened, to the beautiful
Santa Cruz campus.
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GENESIS
In spite of his insanely busy schedule as faculty member in two
departments, supervisor of two laboratories, and mentor to several
graduate students and postdocs, Dave was a gracious and attentive
host. He welcomed me to his biochemistry lab and we set to work
immediately.
Once I had opened the capsules (which responded with the now
familiar bang! and intense oily foaming), he led me step-by-step
through the chloroform extraction, concentration, and preparation of
a 10 × 10-inch glass plate for chromatography. I had pored over his
1989 paper several times, so it was a delight to duplicate that work with
my own samples under his supervision.
Within a couple of hours, I had decorated a glass plate with a small
yellow-brown dot of unknown chloroform-soluble compounds. We
gently lowered the plate into a deep glass tank into which I had poured
a half-inch layer of pungent ether. (The strong smell triggered a brief,
vivid flashback to an early childhood moment—a menacing masked
anesthesiologist bending over me, smothering my face prior to a ton-
sillectomy. I had to shake away the disturbing image.) As with Deamer’s
earlier work, the solvent pulled the glass plate’s single yellow-brown
spot into a long streak. Then we rotated the plate and the chloroform
smeared the streak into what we hoped would be a distinctive pattern
of organic compounds.
I felt more than a little tingle of anticipation as the lights went out
and the UV fluorescent lamp flicked on. The results were gorgeous! A
brilliant yellow, blue, and purple pattern appeared, blazing across the
plate in a diffuse 7-inch-long arc of color. We were delighted to see
several distinctly fluorescing areas, strikingly similar in detail to the
Murchison sample [Plate 6]. Noting the correspondence, Dave sug-
gested that we first concentrate on a blue fluorescing area most closely
matching the position of his original “spot 1.”
Again, we followed the 1988 procedures: Carefully mark the glass
plate, scrape off the white powder from the area of interest, wash that
powder with chloroform to redissolve the fluorescing molecules,
and dry the extract (by this time the lab area smelled strongly of the
chloroform–ether mix). Then the big test. Would my concentrated
extract perform the self-organization trick?
The test was quick and easy. We applied a bit of the extract to a
droplet of water on a glass slide and watched in the microscope, which
used a UV light to highlight fluorescent molecules. Sure enough, tiny
ISOLATION
151
green fluorescing spheres appeared, like a fantastic display of Christ-
mas lights. [Plate 7] Beautiful, but were they vesicles that trapped the
surrounding liquid, or simply solid spheres? That was key to deter-
mine if we had really made cell-like bilayer membranes.
Deamer’s technique was to repeat the microscope observations,
but this time starting with a strongly fluorescing red dye in the water.
For a second time he applied a bit of the extract to the water and, once
again, green fluorescing spheres formed. If we had made hollow
vesicles, then they would capture the distinctive red dye. To find out,
Dave carefully flushed the slide with new, nonfluorescing water. Lo and
behold, the centers of the tiny green vesicles glowed red. We knew we
had made bilayer membranes from nothing more than pyruvate and
water.
We celebrated that night with a bottle of Napa Valley cabernet and
talk of next steps and publications. We both knew that the pyruvate
results were at best a footnote to the Murchison and NASA Ames dis-
coveries, but the experiments seemed to underscore the inevitable
emergence of self-organizing molecular systems along the path to life.
To be sure, many problems remain to be solved. Recent work by
Deamer’s group suggests that lipid self-organization may be sharply
limited by the presence of dissolved calcium and magnesium, seawater
ingredients that would have been present in significant concentrations
in Earth’s early ocean. Perhaps life can begin only in fresh water, or
maybe some as yet unidentified varieties of lipid molecules were in-
volved. And, as many biologists have been quick to point out, the
vesicles produced in Deamer’s work are a far cry from actual cell mem-
branes, which feature a mind-boggling array of protein receptors that
regulate the flow of molecules and chemical energy into and out of the
cell.
These details will occupy researchers for decades to come, but the
emergence of cell-like vesicles from simple molecules is now one of the
best-understood features of life’s origin.
AEROSOL LIFE
New ideas about the emergence of self-organized molecular systems
keep origin-of-life workers on their toes. An especially intriguing re-
cent proposal comes from Oxford chemist Christopher Dobson and
his collaborators at the National Oceanic and Atmospheric Adminis-
152
GENESIS
tration (NOAA) in Boulder, Colorado. In 2000, they published a specu-
lative yet persuasive hypothesis on lipid self-organization in the Pro-
ceedings of the National Academy of Sciences. Elaborating on earlier
unpublished work by the geophysicist Louis Lerman at Stanford,
Dobson’s group focused on the possible roles of atmospheric aerosols
in prebiotic synthesis and molecular organization.
Many organic molecules—especially lipid molecules like the ones
Deamer isolated from the Murchison meteorite—could have accumu-
lated at the ocean’s surface like an oil slick. As wind kicked up white-
caps and waves crashed onto the earliest shores, a continuous fine mist
of aerosol particles—tiny droplets, some smaller than a thousandth of
an inch across—would have sprayed into the atmosphere from the oily
surface. Each water droplet would have contained a significant con-
centration of organic molecules that almost immediately would have
formed a membranous shell around the wet interior. The largest of
these droplets would have fallen quickly back into the foam, but smaller
aerosol particles are quite robust and could have remained suspended
in the atmosphere for months or even years, riding wind currents like
microscopic gliders high into the stratosphere.
Dobson and colleagues speculate that lipids in each aerosol par-
ticle formed a spherical, si
ngle-layer structure with the hydrophobic
ends facing the atmospheric exterior and the hydrophilic ends facing
the aqueous interior. Many of these aerosol particles would have incor-
porated reactive, water-soluble organic molecules, which might have
undergone further chemical reactions in sunlight. Each particle would
have had weeks or months to experience such energetic transforma-
tions; each would have been, in effect, a tiny chemical experiment.
For hundreds of millions of years, aerosol particles in numbers
beyond imagining drifted into the skies. Upon their return to the ocean,
each hydrophobic aerosol particle would have been spontaneously
coated by more lipid molecules at the ocean’s surface to form a bilayer
structure—the emergence of the familiar membrane structure of cel-
lular life. In the words of Dobson, “Organic aerosols offer more than
freedom from the tyranny of the tidal pool or Darwin’s ‘warm little
pond’; they offer a possible mechanism for the precursory production
and the subsequent evolution of populations of cells.”
In either scenario, whether in the form of wind-blown aerosols or
water-bound vesicles, lipid self-organization seems to have been an es-
sential step in isolating the insides from the outsides of cell-like struc-
ISOLATION
153
A
B
C
D
According to the theory of Christopher Dobson and colleagues, the surface of the
ancient ocean was coated with amphiphilic molecules. The action of ancient waves
and winds would have formed aerosol particles surrounded by lipid molecules (A).
These particles might have remained in Earth’s atmosphere for months (B), but
would eventually return to the ocean (C), and form cell-like bilayer structures (D) (after Dobson et al., 2000).
tures. But a membrane, by itself, is not life. Other essential
biomolecules, including proteins, carbohydrates, and nucleic acids, had
to be assembled from the soup. The trouble is that the building blocks
of these macromolecules—amino acids, sugars, bases—are all water
soluble. By themselves, they can’t self-assemble in water.
What to do? Call in the rocks.
12
Minerals to the Rescue
But I happen to know exactly how life arose; it’s brand-new
news, at least to the average layman like yourself. Clay. Clay is
the answer. Crystal formation in fine clays provided the
template, the scaffolding, for the organic compounds and the
primitive forms of life. All life did, you see, was take over the
phenotype that crystalline clays had evolved on their own.
John Updike, Roger’s Version, 1986
The first living entity emerged from interactions of air, water, and
rock—the same raw materials that sustain life today. Of these three
chemical ingredients, rocks—and the minerals of which they are
made—have generally received little more than a footnote in theories
of life’s emergence. The atmosphere and oceans have long enjoyed the
starring roles in origin scenarios, while rocks and minerals sneak in
and out as bit players—or simply as props—and then only when all
other chemical tricks fail.
Some recent and fascinating experiments promise to change that
misperception. Origin-of-life researchers have begun to realize that
minerals must have played a sequence of crucial roles, beginning with
the synthesis of biomolecules and during their subsequent assembly
into growing and evolving structures.
The Miller–Urey chemical process works by ionizing gas mol-
ecules—blasting them with lightning or ultraviolet radiation and
thereby stripping off electrons, so that small groups of atoms readily
recombine into larger organic molecules. Interesting molecules inevi-
tably emerge, but those energetic processes effectively prevent the for-
mation of essential macromolecular structures, including the polymers
and membranes required by all known life-forms. The Miller–Urey
155
156
GENESIS
scenario can’t have been the entire story. That’s why many researchers,
especially those trained in geology, turn to rocks and minerals.
MINERALS AS PROTECTION
Rocky outcrops and overhangs—especially in tidal zones, where sea-
water evaporates and thus concentrates organic molecules—might
have promoted macromolecular formation. Imagine a shaded cove
where increasingly concentrated mixtures of organic molecules accu-
mulated and reacted, protected by a rocky ledge from the Sun’s harm-
ful radiation. Rocks might have served as Earth’s earliest sunblock.
They may well have provided protection at a smaller scale as well. Many
volcanic rocks of the early Earth were laced with countless air pockets
left by expanding volcanic gases. Evaporating seawater might have de-
posited a rich mix of organic molecules in such tiny hollows, each like
a small test tube where further reactions could proceed.
Mineralogist Joseph V. Smith, professor emeritus at the University
of Chicago, envisions even smaller protected environments. He cites
electron microscopy studies of weathered mineral surfaces, which of-
ten display myriad microscopic cracks and pores. Feldspar, the com-
monest of all rock-forming minerals, sometimes features millions of
tiny weathered pockets, each the approximate size and shape of living
cells, each providing a place for molecules to congregate, each pore and
crack a separate experiment in molecular self-organization. [Plate 7]
POLYMERIZATION ON THE ROCKS
The production of macromolecules requires two concerted steps: The
correct molecules must first be concentrated and then organized into
the desired structure. In the case of lipid membranes, these two tasks
occur virtually simultaneously and spontaneously; lipids in water sepa-
rate and self-organize into a bilayer. But other key biological macro-
molecules, including proteins and carbohydrates, form from
water-soluble units—amino acids and sugars. Consequently, they tend
to break down, not form, in water.
One promising way to assemble such molecules from a dilute so-
lution is to concentrate them on a surface. For decades, the prevailing
paradigm has been that the molecules of life assembled at or near the
ocean–atmosphere interface. The surface of a calm tidal pool, or per-
MINERALS TO THE RESCUE
157
haps a primitive slick of water-insoluble molecules might have done
the job. But then, as noted, these environments are open to lightning
storms and ultraviolet radiation.
Origin scientists with a penchant for geology have long recognized
that rocks might provide attractive alternative surfaces for concentra-
tion and assembly—a kind of scaffolding for the assembly of protolife.
More than a half-century ago, the British biophysicist John Desmond
Bernal advocated the special role of clays, which are ubiquitous miner-
als with regularly layered atomic structures.
Clays come in a wide range of compositional and structural vari-
ants, but
all of them feature layers of strongly bonded silicon and alu-
minum atoms. The proclivity of clays to exhibit a surface electrostatic
charge enhances their ability to adsorb organic molecules—a kind of
molecular-scale static cling. What’s more, clays tend to occur as excep-
tionally fine-grained flat particles. Consequently, a palm-sized pile of
ordinary clay can boast a reactive surface area greater than 1,000 square
feet.
Subsequent experiments have supported Bernal’s speculations. In
a 1978 study, Israeli biochemist Noam Lahav and colleagues discov-
ered that amino acids concentrate and polymerize on clays to form
small, protein-like molecules. Such reactions occur when a solution
containing amino acids evaporates in the presence of clays—a situa-
tion not unlike the evaporation that dries up a shallow pond or tidal
pool. Of special note is the fact that this process relies on cycles of
heating and evaporation—and cycles, recall, are one of the key factors
in the emergence of complexity. Patterns of daily and seasonal changes
doubtless fostered the emergence of new molecular structures.
More recently, research by NASA-sponsored teams in California
and New York has demonstrated that a variety of layered minerals can
adsorb and assemble a variety of other organic molecules. In a tour de
force series of experiments during the past two decades, chemist James
Ferris and colleagues at Rensselaer Polytechnic Institute induced clays
to act as scaffolds in the formation of RNA, the polymer that carries
the genetic message enabling protein synthesis.
Ferris relied on the simplest of procedures. First, he prepared a
solution of “activated” RNA nucleotides, each consisting of a ribose
sugar bonded to a phosphate and a base, plus a reactive molecule called
imidazole that promotes, or “activates,” bonding between nucleotides.
Such a solution can sit on the lab bench for weeks with little change.
158
GENESIS
But sprinkle in a bit of a suitable clay mineral and the RNA pieces start
to link up. In a matter of hours, lengths of 10 nucleotides form. By the
end of 2-week experiments, the RPI team produced RNA strands of
more than 50 nucleotides. The fine-grained clay particles had induced
polymerization by a process not yet fully understood.
Buoyed by the Ferris team’s success, other origin-of-life research-