Life’s Origins 161There are many possibilities for natural substances that could produce just such a tem-
plate for organic molecules. The best-known candidates are the minerals known as zeolites,
which are complex silicate minerals typically formed by the breakdown of volcanic glass in
hot gas bubbles left in lava. Zeolites have a complex, repetitious mineral structure that helps
them catalyze organic reactions and make these reactions go much faster. In fact, they are
heavily used in industrial settings for just that purpose, especially in petroleum refining, in
filtration, and in absorbing chemicals (hence their use in kitty litter). All it would take is a
few zeolites in a primordial soup, and the amino acids could be lined up into much more
complex proteins.
An even more daring idea was posed by Alexander Graham Cairns-Smith, who sug-
gested a template more humble than zeolites: common clay. Just as God supposedly created
Adam and Eve out of clay, Cairns-Smith argues that the complex open-layered structures
of clay minerals (which are sheet silicates, like micas) are ideal for absorbing organic mol-
ecules and lining them up along the clay mineral structure. The basic sheet structure of clay
minerals is repeated again and again, with small imperfections in the crystals, compara-
ble to mutations in the genetic code. In fact, Cairns-Smith takes the idea one step further.
He argues that life began as clay minerals that copied themselves over and over again (with
the mutations) during the crystallization process. Clays can grow, modify their environment,
and replicate in a very low-tech version of life. Cairns-Smith then argues that the high-tech
nucleic acids that had been lined up along these replicating clay “life forms” then underwent
a genetic takeover event, and organic “replicators” replaced silicate-based replicators.
Naturally, these highly speculative ideas are very controversial but not impossible given
what we know about the chemistry of clays and organic molecules. But there is one more
possible template to consider: the mineral pyrite, or iron sulfide, FeS 2 , better known as “fool’s
gold.” Gunter Wächtershäuser has shown that pyrite crystals have a positive charge on the
surface that could attract the negatively charged ends of many organic molecules. Once they
are attracted, lined up, and packed close to one another, the organic molecules could easily
link together to form complex polymers. Once linked together, they could unzip from the
pyrite template and float as free biochemicals.
The strength of this suggestion is that it fits another astonishing scientific discovery:
the “black smokers” at the bottom of the sea (fig. 6.6). In 1977, scientists using small sub-
marines floated over the midocean ridges on the deep seafloor, where seafloor spreading
takes place and new oceanic crust is generated. They were astonished to find places where
the volcanic heat was superheating the seawater and producing submarine hot springs,
with jets of near-boiling water shooting upward through chimneys (known as “black
smokers”) composed of pyrite, calcium sulfate, lead sulfide, and zinc sulfide. Living in
this hot, dark environment is a dense population of sulfide-reducing bacteria, some of the
most primitive life forms on earth, which take hydrogen sulfide (H 2 S, which produces the
“rotten egg” smell) and metabolize it, using it instead of water as the source of their hydro-
gen. These bacteria thus use chemosynthesis to power life because there is no light and there-
fore no possibility of photosynthesis or plant life (in contrast to most other environments on
earth). Feeding on this bacterial population was a huge community of bizarre animals never
seen before, including gigantic clams, huge tube worms, weird crabs, and some animals that
were entirely new to science. I vividly remember working in the lab as a graduate student
at Woods Hole Oceanographic Institution in Cape Cod in the summer of 1978 and attending