2009 进军美利坚作文组 wondersmiths2第十一次作业 8.28

wondersmiths2UID：2609756

高分120 practice 4
In the lecture, the speaker talks about the cause of Tunguska explosion. She strongly disagrees with the arguments stated in the reading passage, due to the following reasons.

Firstly, the fact that there are no traces of impact left in Tunguska is not sufficient to prove that Tunguska explosion was not caused by an asteroid. It is not surprising that the traces have been destroyed by the force of nature after ninety years. So, This directly casts doubts on the point shown in the reading passage.

Secondly, there exist a lot of other causes for the fact that there is no huge crater in Tunguska. Perhaps, the asteroid hit the Tunguska already exploded in the outer space before it landed on ground, or it became a huge fireball above Tunguska so that no crater is left in Tunguska. Hence, the view demonstrated in the reading passage cannot be convincing.

Finally, the speaker raises the issue that if the explosion really was caused by "swamp gas" then there should be no trees in huge areas because of the fire. However, there only exists the butterfly pattern of trees knocked sideways in Tunguska. Therefore, the opinion of the speaker completely is a contrast to the point displayed in the reading passage.