Environmental Engineering Reference
In-Depth Information
more volatile elements such as nitrogen, oxygen and carbon condensed at low
temperatures farthest from the sun, forming outer planets rich in gas-liquid-ice.
Figure 1
Earth and other planets of our solar system. Planetesimals
condensed and concentrated in a rotating disc of planetary matter
around our sun, with early fractionation according to temperature
zones within the disc. (Not to scale.)
Our embryonic Earth gained kinetic and thermal energy through the accretion of mass
and additional thermal energy from crustal radioactivity, creating high temperatures at the
core and raising surface temperatures briefly as high as 8,000° C to 10,000° C. As a
result, planetary materials segregated according to their chemical and physical character,
and Earth's internal structure is a microcosm of the solar system. Its core is surrounded
by five concentric, progressively cooler, less dense and more unstable layers or
geospheres (Figure 10.3). Paralleling the distribution of elements in our solar system
outwards from the sun, high-density stable refractory elements (Ni, Fe) survived in the
core. More-volatile elements formed the mantle (Fe, Mg, Si,) and crust (Mg, Si, Ca, Na,
K, C). The most volatile elements (H, N, O, S) were driven off to form the ocean-
atmosphere systems. Some condensed as fluids (H
2
O), others formed gases (O
2
, N
2
, CO
2
,
CH
4
, NH
3
, NO
2
, SO
2
), whilst some part of the lightest elements were exhaled to space (H,
He). Many of these more volatile elements may be stored as unstable compounds in
Earth's crustal rocks. They are exchanged with the atmosphere or hydrosphere through
the acid/base oxidation/reduction processes referred to in Chapter 1. Human activity,
intentionally or inadvertently, often accelerates the rate and extent of these processes with
increasingly detrimental environmental impacts and climate change.
processes. The
biosphere
itself is a hydrocarbon derivative of geological fractionates
where lithosphere, hydrosphere and atmosphere meet. All three systems respond to
heating,
photodissociation
or fractionation by sunlight, in addition to geological
processes, through biogeochemical reorganization.
