The Tunguska mystery.pptVIP

What happened 100 years ago? June 30 1908 7:14AM. Central Siberia（西伯利亚）-Semen Semenov,a local farmer, saw“the sky split （分裂）in two. Fire appeared high and wide over the forest. From where the fire was came strong heat. then the sky shut close, and a strong thump（重击声） sounded and I was thrown a few yards. After that such noise came, as if cannons（重炮） were firing, the earth shock What happened 100 years ago? Such is the harrowing(悲惨的） testimony（证词） of one of the closest eyewitnesses to what scientists call The Tunguska Event the largest impact of a cosmic （宇宙的）body to occur on the earth during modern human history. Semennov experienced a raging Conflagration some 65 kilometers from ground zero.（爆心投影点 ） The effect of the event But the effect of the blast（爆炸） rippled （波及）out far into northern Europe and central Asia as well, some people saw massive （巨大的）silvery （银色的）clouds and brilliant colored sun sets on the horizon, where as others witnessed luminescent （发光的）skies at night, Londoners for in stance could plainly read newsprint at midnight without artificial lights. Geophysical servatories place the source of anomalous seismic and pressure waves they had recorded in a remote section of Siberia. the epicenter lay close to the River Dudkamenaga Tunguska, an uninhabited area of swampy taiga forest that stay frozen for eight or nine months of the years. Many scientists believe that an asteroid （小行星）or comet （彗星）entered the earth’s atmosphere over central Siberia and exploded between five and 10 kilometers above the ground. The airburst flattened （击倒）about 80 million trees over 2000 square kilometers, which is about four times the area of Lake Tahoe. If the impactor （撞击体）was an asteroid, investigators（研究者） estimate （推断）its diameter （直径）would have ranged from 50 to 80 meters. Searchers have so far fund no remains of the object, which seems to have disintegrated. Ever since the Tunguska event, scientists and lay enthusiasts （狂热者）alike have wondered what caused it. Althoug