162 Evolution? The Fossils Say YES!
a presentation of these remarkable discoveries given by the very scientists who had just
left the submarine. This amazing chemosynthetic community is totally different from the
plant-based photosynthetic ecologies elsewhere on earth. The most important clue is that it
is inhabited by the most primitive life forms known on earth, the sulfide-reducing Archae-
bacteria (fig. 5.6). To many scientists, this suggests that the simplest forms of life arose not on
the surface in Darwin’s “warm little pond,” but in a deep-sea hot spring, where they would
have been protected if impacts vaporized the shallow oceans.
But there is one other issue that has been widely argued among scientists working on
the origins of life: What was the first genetic material? Today, the information for reproduc-
tion and making more copies of living organisms is encoded in the nucleic acids, RNA or
DNA, of each cell. The nucleic acids then code for certain strings of proteins, which are the
stuff of life. But nucleic acids are far more complex and difficult to produce than are proteins,
which we saw are among the easiest long-chain biomolecules to generate. Protein biochem-
ists like Sidney Fox have long advocated that it would be easier for the first self-replicating
organism to make its genetic code out of readily available protein chains (which still execute
the commands of the nucleic acids today). At some later point in time, more complex nucleic
acids were produced that eventually hijacked the system of replication from one protein to
its descendants.
FIGURE 6.6. In the deep volcanic rift valleys of midocean ridges, fresh lava erupts as the oceanic crust pulls
apart. The hot magma heats the seawater percolating through it to superheated temperatures, forming plumes
of boiling water and dissolved minerals known as “black smokers.” The main precipitate of this reaction is
pyrite (iron sulfide, or “fool’s gold”), which is also a good template for bonding together complex organic
materials. Consistent with the hypothesis that life originated in deep-sea vents, biologists have found that the
genetically simplest forms of life, the Archaebacteria, are common in the black smokers. These are the base
of a food chain that includes a huge community of giant clams, tube worms, crabs, and many other unique
creatures found only in these dark submarine communities. Since there is no light at this depth, this entire
system relies not on photosynthesis, but on chemosynthesis, with sulfur-reducing bacteria (rather than plants)
at the base of the food chain. (Photo courtesy NOAA)