Реферат: Earth Impacts as a Threat to Civilization
In recent years we get more& more facts showing that the present appearance of our planet was formednot only by slow evolutionary processes, like wind erosion, but also bygigantic natural cataclysms. Geologists find evidence in sedimentary rock thatextremely powerful impacts repeatedly occurred in the geological history of theEarth.
Since the late Paleozoicperiod (i.e. for the last 250 million years) there are noticeable gaps in theevolution of living organisms. Paleontologists established that around 247, 220and 65 million years ago about 95% of all life on Earth perished. Mostrecently, for example, the gigantic dinosaurs died out. It is obvious that suchextinctions of terrestrial living organisms are the complex result of manyprocesses. Sharp climate variations, ice formations, fluctuation of the levelof oceans, decreases of concentration of oxygen in the waters of seas andoceans, and different extraterrestrial circumstances all played a part.However, to name the most important reason, was extremely difficult todiscover.
Scientistsassumed that at that time the Earth underwent bombardment by large asteroids.Space and aerial photography, executed in slanting solar illumination, revealedlikely asteroid impact sites. Studies at the sites confirmed the Earth’sencounters with celestial bodies.
Impact with an asteroidabout 10 kilometers in diameter is thought to have caused mass death ofdinosaurs. If the impact had arrived on the land, it would have sharplycooled, but if over the surface of ocean or sea, then water vapor would haveproduced a greenhouse effect and begun to warm the Earth everywhere. The Earthmay also have witnessed hot nitric acid rains, whose action on the environmentand the animal kingdom was catastrophic. Such a large impact could occur onEarth every hundred million years. Impacts of a smaller size are more frequentand also less damaging.
It ispossible 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 theasteroid. The purpose of the rocket is not to collide with the asteroid, to explodeclose enough to the asteroid to change its orbit. Smaller asteroids can also becut by lasers, with no effect on Earth.
The technologyof the 21st Century should be able to detect all large asteroids& possible impacts with Earth. We will only have to worry about objectswhose trajectory is very hard to observe. To solve this problem, scientistsneed to see Tunguska-sized asteroids from two points at the same time. Thefuture project of 3 telescopes around Earth’s orbit can make it possible.
We don’t know how much itwill cost, but in comparison with US Government Military Budget, it is verycheap. The Australian Spaceguard Survey estimates the project to cost 10million US dollars per year. The US Government currently spends around 330billion, according to www.whitehouse.gov, on military projects per year. Theimpact prevention projects have the same aim as military projects: to protect.An impact with big asteroid could do much more damage than our strongestmilitary enemy, so we should be able to spend at least 10 million dollars peryear to prevent another catastrophe. I also think all countries in the worldshould be interested in supporting Spaceguard program. It needs to be aninternational collaboration. According to Space Daily, funds for this programare reasonable, at approximately a half a penny (US) per person, per year inthe whole world. Worldwide Spaceguard program does very important mission forthe whole civilization.
AustralianSpaceguard Survey. 22 September 2002.
NASA’s NearEarth Object Program. 22 September 2002.
Department ofDefense. 22 September 2002.
Space Daily. 23September 2002