Geology Reference
In-Depth Information
ily on other sets of mineral surfaces. As handed molecules are separated and concentrated,
each surface becomes a tiny experiment in molecular selection and organization.
On its own, no such natural experiment with minerals and molecules is likely to have
generated life. But take countless trillions of trillions of trillions of mineral surfaces, each
bathed in molecule-rich organic broth, and repeat those tiny natural experiments over
and over for hundreds of millions of years. Earth must have eventually tested virtually
every combination ofsmall molecules somewhere, sometime. The tiny fraction ofall those
molecular combinations that wound up displaying easier self-assembly, or developed a
stronger binding to mineral surfaces, or enjoyed greater stability under the high temperat-
ures and pressures, survived, possibly to grow, possibly to learn new tricks.
We don't yet know exactly which of those myriad possible combinations of molecules
and minerals led to lifelike organization, but the principles of molecular selection and or-
ganization are now emerging. Biomolecules were synthesized in abundance, and some of
those molecules went on to form larger and larger clusters. Our experiments suggest that
electricchargeplayedabigrole.Somemoleculeshaveaslightpositivecharge;othershave
a slight negative charge; and still others (like water) are polar with slightly positive and
negative ends to the same molecule. Minerals, too, have charged surfaces, some positive
and some negative. Add all these charged pieces together, and they spontaneously organ-
ize,withpositiveelectricchargealwaysattractedtonegativeelectriccharge.Andsovaried
molecular assemblies occurred in virtually every wet, mineral-rich environment on prebi-
otic Earth.
Step 3: Replication
Arrays of chemicals, no matter how intricately patterned, are not alive unless they can
make copies of themselves. Life's most distinctive hallmark is reproduction: one consorti-
um of molecules becomes two, two become four, and on and on in geometric expansion.
The greatest enigma in the biogenesis story remains the emergence of that first system of
self-replicating molecules. Clever experiments replicate portions of plausible reproductive
cycles, though we have yet to mimic completely that elusive biochemical trick in the lab.
Nevertheless, at some point in space and time, an organized collection of molecules began
to duplicate itself at the expense of other molecules (that is, “food”).
Imagine Earth at age five hundred million years—roughly four billion years ago. It had
abrothoforganic molecules, ithadtrillions upontrillions ofreactive mineral surfaces, and
it had hundreds of millions of years to play with. Most of the molecular milieu did noth-
ing of interest and displayed no useful functions. But a small fraction of the organic mo-
lecules arrayed on mineral surfaces produced some kind of structure with enhanced func-
tion—perhaps a stronger surface attachment, or maybe the means to attract more molec-
