The reading passage asserts that there are three possible explanations for the mass ext
inction at the end of the Triassic period. However, the speaker challenges each of the
se theories by giving her own arguments.
To begin with, the article points out that the decline of sea level could be the pri
mary cause because it eliminated ideal habitats for creatures that originally lived in
shallow water or coastal areas. This change significantly affected the food chain and e
ventually led to the mass extinction. Nevertheless, the speaker refuted this theory by
arguing that though sea levels did fluctuate during that time, it was a gradual proces
s that allowed enough time for species living in the shallow water and coastal areas
to adapt to the change.
In addition, the article proposes the global cooling theory, which means that the rise
of the level of sulfur dioxide due to volcanic eruption should be to blame, because
it lowered the temperature on earth and subsequent climate change. But the speaker chal
lenges this by offering her contention that excessive sulfur dioxide could combine with
water and thus be eliminated from the atmosphere, so this explanation doesn't stand, e
ither.
2Finally, the article suggested that the collision of an asteroid at the end of the T
riassic period could result in an elongated period when the sunlight was blocked by du
st that generated from the formation of the crater. Again, the speaker refuted this by
pointing out that no evidence could support this theory, since the only crater found
near that time was formed 2 million years earlier than the mass extinction, which had
nothing to do with the extinction.