Environmental Management: Principles and practice

part of a complex system and must fit in, obey the limits or be cut out. If humans
upset Gaian mechanisms, there could be sudden, possibly catastrophic, runaway
environmental changes. Environmental management must assess the reality of this
threat and, if it is significant, monitor for and prevent runaway changes.
Environmental catastrophes and changes
The scale of catastrophes varies from local to global. They may happen every few
years or be millions of years apart, and they may or may not have a predictable
pattern of recurrence. Catastrophes may be sudden, obvious and gradual, or of the
creeping form (where a system is stressed and changes virtually imperceptibly until
a threshold is reached, whereupon there may be sudden drastic alteration). Given
long enough, chance events probably affect the survival of organisms at least as
much as evolution—the process has been described as ‘contingency’ (Gould, 1984).
Events which challenge life but give insufficient time for adaptation would allow
some organisms to prevail for quite fortuitous reasons (rather than ‘survival of the
fittest’).
Early earth scientists invoked catastrophic events to explain erosive land forms,
prehistoric extinctions and geological unconformities (Thomas Huxley probably
coined the term ‘catastrophism’ in 1869). With the publication of The Principles of
Geology in 1830, Charles Lyell helped uniformitarianism (the idea of continuing
gradual change, involving processes operating in the past that operate today) to prevail
over catastrophism, but since the mid-nineteenth century there have been various
attempts to revive it (Smith and Dawson, 1990; Ager, 1993).
A number of scientists recognize mass extinctions, perhaps 15 significant events
in the last 600 million years, the four major ones being: ca. 440 million years BP, ca.
390 million years BP, ca. 220 million years BP, and (the K/T boundary event) ca. 65
million years BP (Raup, 1988; 1993). The cause of mass extinctions is debated, and
some question whether there really is adequate evidence, suggesting instead more
gradual loss of species.
In the early 1980s Walter Alvarez noted the widespread occurrence of iridium
(a rare metal), glass spherules and ‘shocked quartz’ grains in a thin clay layer of K/
T boundary age (Alvarez and Asaro, 1990). This and tsunami beds around the Gulf
of Mexico have been interpreted as evidence of a planetesimal (of roughly 10 km
diameter) impacting with the Earth (Kerr, 1972). Others suggest that a very large
sheet-lava eruption, possibly the outpouring of the Deccan Plateau Basalts of India
caused the extinctions. These are by no means the only causes suggested by supporters
of the K/T mass extinction. Others include: climate change, sea-level falls, reduction
of atmospheric oxygen levels, disease, etc.
Whether or not a planetesimal strike caused the extinction of the dinosaurs or
caused earlier and subsequent disruptions, there is enough evidence of impacts to

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indicate a threat that environmental managers should seriously consider. Over 100
ancient craters, a few of more than 100 km diameter, are known on Earth and some
are as recent as 1500 BP (Huggett, 1990). A small body (estimated 100 metres
diameter) probably exploded about 8 km up at Tunguska, Siberia, in AD 1908,
flattening 1200 to 2200 km
2
of taiga forest. A similar strike may have occurred in
South Island, New Zealand, ca. 800 BP (Hecht, 1991), and a blast (of about 100
kilotons yield) in the South Atlantic in 1978 may have been caused by a planetesimal
(Lewin, 1992). The impact of a 1-km diameter body would probably endanger
civilization.
Volcanic eruptions can be locally devastating (e.g. Pompeii and Herculaneum
—AD 79; Hekla, Iceland—AD 1636; Tambora, Indonesia—AD 1815; Krakatoa,
Indonesia—AD 1883), and large outpourings of lava or eruptions of ash, gases and
aerosols into the stratosphere could alter climate and cause acid fallout. Smaller
eruptions like El Chichon (Mexico—1982) and Mt Pinatubo (Philippines—1991)
caused temporary slight lowering of global temperatures. Palaeoecologists and
archaeologists have correlated past eruptions, acid deposition in Greenland ice and
alteration of climate affecting human fortunes in Europe.
The recurrence of catastrophic events may not be random: planetesimal strikes,
variation in Earth’s solar radiation receipts and perhaps vulcanicity and seismic
activity might be more likely at certain alignments in the orbits of the planets or
perhaps as the solar system passes the galactic plane every 26 to 33 million years.
Velikovsky (1950; 1952; 1955) suggested that planetary alignments within the solar
system could be blamed for catastrophic events. However, this, and a modern variant,
the ‘nemesis’ hypothesis have won only limited support. The nemesis hypothesis,
suggests that a hidden companion star to the Sun in an eccentric orbit periodically
affects the solar system enough to alter climate and possibly trigger volcanicity.