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Topic 14
Reading
In the late June of 1908, a fireball exploded above the remote Russian forests of Tunguska, Siberia, destroying more than 800 square miles of trees. While scientists think the Tunguska explosion was caused by an asteroid, recent studies have shown that the event was most likely the result of a “swamp gas” explosion, rather than an object from outer space. Here is why.
First of all, if an asteroid exploded above Tunguska, it would have left some traces at the impact site. But so far neither its fragments nor any impact craters have been discovered in Tunguska after repeated expeditions. In January 2001, a meteoric explosion took place over Canada. The meteoric explosion left abundant fragments. Therefore, if the same event happened in Tunguska, something would be found.
Second, if it was a large asteroid that slammed into Earth, the impact on land would have caused a huge crater. Researcher first proposed the Lake Cheko, a 164-foot-deep lake located just 5 miles northwest of the epicenter of the destruction, might have been the impact crater. Nevertheless, researchers concluded that was not an impact crater. Without a smoking gun, the asteroid impact theory simply could not hold.
Finally, judging from the butterfly pattern of trees knocked sideways in Tunguska, the explosion must have occurred close to the ground. Note that the Tunguska is a swampland extending to thousands of kilometers. In the beginning of summer, all swamps in the region would be defrosting, releasing in a very short time a large quantity of “swamp gas,” or methane gas. Scientists point out that the most likely culprit was a huge cloud of well mixed methane and air, which was common in Siberia. The truth is, comets and meteors do not explode when encountering Earth’s atmosphere.
Topic 14
Listening
The Tunguska explosion is the largest impact event in recent history. This explosion has sparked heated debates in the science community. The latest explanation for the Tunguska event is a methane gas explosion, but I don’t find it convincing.
First of all, those for a methane gas explosion claim that the lack of asteroid or comet particles at the Tunguska explosion site proves that the impact was unlikely to be caused by an asteroid. But the absence of asteroid fragments doesn’t mean that the asteroid did not hit Tunguska. It was 19 years after the Tunguska explosion that scientists went to the scene to find evidence. Any traces left at the impact site would have been destroyed by the forces of nature. In contrast, just two weeks after the meteoric explosion occurred in Canada, scientists rushed to the site to search for meteoric remains.
Second, those against the asteroid theory argue that if an asteroid slammed into the Earth, the impact would have caused a huge crater on Earth. However, the asteroid did not have to crash into the Earth as an intact rock. When an asteroid or comet enters the Earth, it could explode in the lower atmosphere before hitting the ground. Under rapid heat and pressure, the space rock slamming into the Earth could have exploded into a huge fireball over Tunguska. If so, there would not be any crater at Tunguska.
Finally, if it was methane gas that caused the Tunguska explosion, the huge fireball would not have concentrated on one spot. As a matter of fact, the traces of Tunguska explosion have a single epicenter of destruction. The single epicenter was more likely to be caused by an asteroid rather than a swamp gas blast.