Environmental Engineering Reference
In-Depth Information
2
P
LANETARY
E
NERGETICS
Atmosphere, Hydrosphere, Lithosphere
. . . consider first of all
Seas, lands, and sky; those threefold essences,
Those bodies three, those threefold forms diverse,
Those triple textures vast . . .
Lucretius (c. 99-c. 55
B
.
C
.
E
.), De Rerum Natura
planet's atmospheric circulation and its massive water
cycle, the two processes that redistribute heat and mois-
ture and that are responsible for atmospheric and hydro-
spheric fluxes ranging from ephemeral (lightning) to
continuous (rivers), from highly localized (tornadoes)
to very extensive (monsoon). And only a tiny part of the
received radiation is converted by photosynthesis into
phytomass, whose production sustains an enormous vari-
ety of heterotrophs.
But photosynthesis needs much more energy indi-
rectly. Without surface temperatures high enough to
keep water liquid (at least seasonally) and to allow for
rapid rates of biochemical reactions, there would be no
excitation of chlorophyll, no absorption of nutrients
through roots, no decomposition of dead organic mat-
ter. And solar energy transformed into winds and
flowing water has indispensable indirect roles in photo-
synthesis, ranging from pollination of tens of thousands
of gymnosperm and angiosperm species to denudation
Even when compared to its closest planetary neighbors
the Earth is unique. Its improbable atmosphere is domi-
nated by molecular nitrogen and oxygen and contains
many trace gases (CH
4
,N
2
O, NH
3
) whose concen-
trations violate the rules of equilibrium chemistry to an
infinite extent (Lovelock 1979). This atmosphere is a
creation of life. The atmosphere of a lifeless Earth would
resemble those of Venus and Mars: 98% CO
2
, less than
2% N
2
, and a mere trace of O
2
; the surface temperature
would be about 563 K (290
C), above the melting point
of tin (232
C); and the surface pressure would be a few
MPa rather than just 101.325 kPa (1 atmosphere). Only
a small share of solar radiation is needed to power the
