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Реферат Earth Impacts as a Threat to Civilization

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Текст реферата Earth Impacts as a Threat to Civilization

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Earth Impacts as a Threat to Civilization.
University of Minnesota.
Natalya S. Myers
September 24,2002
In recent years we get more & more facts showing that the present
appearance of our planet was formed not only by slow evolutionary
processes, like wind erosion, but also by gigantic natural cataclysms.
Geologists find evidence in sedimentary rock that extremely powerful
impacts repeatedly occurred in the geological history of the Earth.
Since the late Paleozoic period (i.e. for the last 250 million years)
there are noticeable gaps in the evolution of living organisms.
Paleontologists established that around 247, 220 and 65 million years
ago about 95% of all life on Earth perished. Most recently, for
example, the gigantic dinosaurs died out. It is obvious that such
extinctions of terrestrial living organisms are the complex result of
many processes. Sharp climate variations, ice formations, fluctuation
of the level of oceans, decreases of concentration of oxygen in the
waters of seas and oceans, and different extraterrestrial
circumstances all played a part. However, to name the most important
reason, was extremely difficult to discover.
Scientists assumed that at that time the Earth underwent bombardment
by large asteroids. Space and aerial photography, executed in slanting
solar illumination, revealed likely asteroid impact sites. Studies at
the sites confirmed the Earth’ s encounters with celestial
bodies.
Impact with an asteroid about 10 kilometers in diameter is thought to
have caused mass death of dinosaurs. If the impact had arrived on the
land, it would have sharply cooled, but if over the surface of ocean
or sea, then water vapor would have produced a greenhouse effect and
begun to warm the Earth everywhere. The Earth may also have witnessed
hot nitric acid rains, whose action on the environment and the animal
kingdom was catastrophic. Such a large impact could occur on Earth
every hundred million years. Impacts of a smaller size are more
frequent and also less damaging.
It is possible to detect dangerous objects decades before their
collision with Earth. Scientists use telescopes to calculate the speed
& orbit of an asteroid. The best way to change the trajectory of
motion is to send a rocket towards the asteroid. The purpose of the
rocket is not to collide with the asteroid, to explode close enough to
the asteroid to change its orbit. Smaller asteroids can also be cut by
lasers, with no effect on Earth.
The technology of the 21 st Century should be able to detect all
large asteroids & possible impacts with Earth. We will only have to
worry about objects whose trajectory is very hard to observe. To solve
this problem, scientists need to see Tunguskasized asteroids from two
points at the same time. The future project of 3 telescopes around
Earth’ s orbit can make it possible.
We don’ t know how much it will cost, but in comparison with US
Government Military Budget, it is very cheap. The Australian