Botkin Environmental Science Earth as Living Planet 8th txtbk

106 CHAPTER 6 The Biogeochemical Cycles
Oil and gas is transported
below and on top of
the water by ocean
current and
wind
Wind and current
Air
Water
Seabed
Folded rock
(anticline)
(a)
Deposition of oil
on seabed is
degraded by
microbes
Microbes consume oil and gas
in water column and oil on
seabed (often in a mat)
Fracture (fault) oil
and gas (bubbles)
move up
(b)
FIGURE 6.2 (a) Idealized diagram of physical, chemical, and biological processes with shallow methane
and oil seeps; (b) small bubbles of methane (~1 cm) from a seep at Coal Oil Point on the seabed; and
(c) methane bubbles (~1 cm) at the surface. (Photographs courtesy of David Valentine.)
(c)
6.1 Earth Is a Peculiar
Planet
Our planet, Earth, is unique, at least to the extent that
we have explored the cosmos. In our solar system, and
in the Milky Way galaxy to the extent that we have
observed it, Earth is the only body that has the combination
of four characteristics: liquid water; water at its
triple point (gas, liquid, and solid phases at the same
time); plate tectonics; and life (Figure 6.3). (Recent
space probes to the moons of Jupiter and Saturn suggest
that there may be liquid water on a few of these
and perhaps also an equivalent of plate tectonics. And
recent studies of Mars suggest that liquid water has
broken through to the surface on occasion in the past,
causing Earthlike water erosion.)
The above discussion leads to consideration of
the history of Earth over billions of years. This has
prompted some geologists to propose “big history”—
to link contemporary history with geologic history,
perhaps even going back all the way to the Big Bang