Geology Reference
In-Depth Information
NASA, whose science funding is tied closely to the prospect of great discoveries,
jumped at this possibility. If life is constrained to arise in a Miller-Urey scenario, at the
sun-drenchedsurfaceofawateryworld,thenEarthandpossiblyMars(initsearlieststages,
its first five hundred million years) are the only plausible living worlds within our reach.
But if life can emerge from the black, hot depths of a subsurface volcanic zone, then many
additional celestial bodies become tempting targets for exploration. Mars today must have
deephydrothermalzones;perhapsendureslivesthereevennow.SeveralofJupiter'smoons
arealsoripeforbiologicalinvestigation,asisSaturn'sorganic-rich,Earth-sizemoonTitan.
Even some of the larger asteroids may have deep, life-producing, hot wet zones. If life
arose deep on Earth, then NASA's search (and funding) for exobiology will surely last for
many decades.
My Carnegie Institution colleagues and I are relative latecomers to the origins game.
Our lab's first NASA-sponsored experiments in 1996 were specifically designed to test or-
ganic synthesis in black smoker regimes, where high temperatures and pressures prevail.
Like Miller, we subjected mixtures of simple gases to energetic conditions—in our case,
heat and chemically reactive mineral surfaces, just as you'd find in a deep volcanic zone.
Like Miller, we produced amino acids, lipids, and other bio-building blocks. Our results,
now duplicated and expanded in numerous labs, show beyond a doubt that a suite of life's
molecules can be synthesized easily in the pressure-cooker conditions of the shallow crust.
Volcanic gases containing carbon and nitrogen readily react with common rocks and sea-
water to make virtually all of life's basic building blocks.
What's more, these synthesis processes are governed by relatively gentle chemical re-
actions called reduction and oxidation reactions, or redox reactions, such as the familiar
rusting of iron or caramelizing of sugar. These are the same kinds of chemical reactions
that life uses in metabolism, in sharp contrast to the violent ionizing effects of lightning
or ultraviolet radiation. Indeed, while harsh lightning bolts may facilitate the production of
small biomolecules, they just as easily rip those building blocks to molecular shreds. To
many of us in the origins game, it makes a lot more sense for Earth to have made its pre-
biotic molecules with less energetic chemical reactions, in more or less the same way that
cells do it today.
Stanley Miller and his followers did what they could to squelch our conclusions and
abort our research program. In a flurry of critical publications, they argued that the high
temperatures of the volcanic vents would quickly destroy any useful biomolecules. “The
vent hypothesis is a real loser,” Miller complained in a 1998 interview. “I don't understand
why we even have to discuss it.” They based their arguments on meticulous experiments
in which biomolecules degrade in boiling water.But these simplistic studies failed to mim-
ic the complexity of primordial Earth; missing were the deep ocean's extreme gradients of
temperatureandcomposition,theturbulentflowandcyclingofvolcanicvents,thechemic-
