Geology. Козлова Е.П. - 43 стр.

in the form of lava. As to elastic deformations accumulated at the sites of plate
collisions or extensions, they are ultimately released in earthquakes, which, among
other things, may also by cosmic factors, e.g. planetary gravitation changes, celestial
bodies, and meteorites. These hitting the earth, give off huge amount of energy that
modifies its surface.
       And more: the mass extinctions of certain plant and animal species in the last
billion years, as some scientists believe, exhibited a definite periodic pattern and –
what is most surprising indeed – concurred with the collisions of our planet with the
heavenly bodies, the asteroids. A similar event took place 65 million years ago when
many species disappeared from the face of the earth, among them, dinosaurs,
cephalopod mollusks, plankton foraminifera, the absolute majority of bivalved and
gastropod mollusks, and so forth. Such wholesale extinctions occurred between the
Paleozoic and the Mesozoic, and the end of the Devonian, between the Proterozoic
and Paleozoic, and in other periods.
       Some natural processes touch man and his living conditions, though the effect
is not as immediate. These are regional and global desert encroachments, soil erosion,
karst formation processes, changes in the level of the World Ocean and the like.

                         Natural Medium Under Pressure

      Today the anthropogenic (maninduced) effect on the lithosphere, the
atmosphere and the hydrosphere, large-scale and pervasive as it is, is fraught with
consequences. For one, it results in global changes of the climate and rapid desert
encroachment. The combustion of vast amounts of mineral fuel fills the atmosphere
with carbon dioxide, sulfur compounds and water vapor; all that intensifies the
hothouse effect. In a follow-up of this global process, the surface air temperature has
been increasing fact in the past 20-25 years. The rate of this increase is much above
the temperature rises of the Quaternary and even those that took place in the distant
geological past.
       Global warming is increasingly impacting the natural landscapes: warmer
climatic zones are encroaching on polar regions. Consequently, tundra and forest-
tundra landscapes are deteriorating fast, and the ice-belts of northern seas are
shrinking. The rapid thawing of ice covers in both hemispheres as a result of higher
temperatures may cause a significant rise in the level of the World Ocean whose
swelling waters would flood vast tracts of lowlands.
      There are changes in the location of humid and arid zones. Belts of steppes and
forest-steppes are expanding northwards, with deserts and semideserts moving next.
Simultaneously, arid zones are contracting because of the intensive evaporation
process touched off by global warming. Permafrost areas are shrinking too.




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