Geology Reference
In-Depth Information
fering greatly as they are cut off from their traditional feeding and breeding grounds.
Further assaults on Gaia's icy realms are taking place in the world's glaciers, which are
extremely sensitive to climate change. Most glaciers decreased in length during the last
century, but a few, notably those in Norway, have expanded. The observed retreat of
global glaciers is consistent with a global warming of between 0.46
0
and 0.86°C over
the last 100 years.
Gaia's icy realm also extends into the great regions of permafrost up in the high
northern latitudes, where the subsoil has remained frozen for several thousand years
to depths of up to 1,600 metres. Vast areas of our planet's land surface, about 25% of
the total, are covered by permafrost, including half of Russia and Canada and 82% of
Alaska. Every summer the uppermost layers of permafrost melt in the sunshine, but as
climate change takes hold the melting goes deeper and the permafrost slowly retreats
northwards. Permafrost holds huge amounts of organic carbon (about one-seventh of
the world's total), mostly in the dead bodies of mosses and other plants, and its melt-
ing gives microbes access to huge amounts of organic material—food to them. As they
binge on this vast bonanza, the microbes release carbon dioxide and methane to the at-
mosphere, contributing another twist to the multifarious and accumulating positive feed-
backs that are warming our planet.
Much of the permafrost forms in gravelly or silty soils held together by ice, and when
this melts the ground becomes slushy and deforms. In parts of Alaska, this thaw-in-
duced subsidence has caused deformations of up to 2.5 metres, and with it the collapse
of buildings and pipelines. The loss of the permafrost has severe consequences for the
traditional peoples of the high Arctic, who find it much more difficult to hunt in the
soggy ground, and their prey, notably the reindeer, also face difficulties because their
migration routes are altered by the melting ground. The thawing in the far north is also
changing biotic communities as fens and bogs invade birch forest.
But another, possibly greater danger lurks in the permafrost and in some of the con-
tinental shelves of the world's oceans. In such places, where temperatures and pres-
sures are just right, a remarkable association takes place between two of Gaia's key
chemical beings—water and methane—giving rise to the increasingly infamous 'meth-
ane hydrates'. In these curious structures, water abandons its usual penchant for mak-
ing hexagonal ice molecules and assembles itself instead into curious cubic cages of ice
with up to eight 'guest molecules' of methane in cordial repose at the centre of each wa-
ter cage, made up by no less than 46 water molecules. The methane comes, of course,
from the activities of decomposing bacteria which live, as they have since Gaia's earli-
est days, in sediments poor in oxygen but rich in the dead bodies of creatures from the
upper airy, sunlit reaches of the planet. Apart from an abundant supply of methane and
water, low temperatures and high pressures are absolutely indispensable for the appear-
