Geology Reference
In-Depth Information
and nutrients, and live in a vast variety of habitats: from deep, hot smoking volcanic
vents at the bottom of the ocean, to bare rock surfaces exposed to wind, rain and intense
sunshine. Ever since their appearance at the beginning of the Archean eon some 3,500
million years ago, bacteria have operated a tightly coupled metabolic network spanning
the entire globe which has ensured that the earth's surface has remained within habitable
bounds.
Bacteria Rule the World
To most people bacteria are nothing more than bringers of disease to be eradicated at all
costs, but in fact only a small minority are pathological to humans. Most are engaged
in the nitty-gritty, everyday work of keeping the planet alive by capturing energy, re-
cycling and decomposing. But before we take a look at how bacteria do these marvel-
lous things for Gaia, we need to learn something about them as individual beings. Let's
shrink ourselves down so that we are only about 1/500th of a millimetre long, about the
size of an
Escherichia coli
cell, a bacterium of about average size. Let's dive down into
the soil, a place where bacteria teem in vast numbers; an average gram of soil contains
millions of bacterial cells of many types.
There ahead of us in the gloom lies a single bacterium—a huge soilstraddling zep-
pelin. It feels squishy to the touch, like a water-filled balloon, for the cell's watery in-
terior is bounded by a tough outer membrane that our puny sub-microscopic fingers can
prod but not break. This is the microbe's cell membrane, studded with countless tiny
pores through which even tinier molecules of food and waste constantly stream in and
out. Brace yourself, for now we'll shrink down small enough so that we too can pass
through a pore into the interior of the cell.
Here in the intense gloom we see a rich soup of molecular beings dashing about in
a seemingly random frenzy. Snaking through them all like a twisted rope is the bacteri-
um's genetic material, its DNA, which coils off into the distance like a giant earthworm
plunging into the soil. We swim right up and tag the DNA rope with a red handker-
chief and set off to see where it will lead us. As we move along the strand, our vista
is unchanged—everything around us appears to be an undifferentiated mass of frenzied
molecular movements. We travel for several hours, and there is no change in what we
see, until there in the gloom we see a little red speck stuck to the DNA strand—it's our
handkerchief! We've discovered that the strand is in fact a great
circle
of DNA.
We've learnt several interesting things from this brief journey to the bacterial world.
The first is that the inside of our bacterium has very little structure—just about the only
large organised thing we found was the long, circular rope of genetic material—the
