Welcome to Mr Aslanov’s Lessons QUESTION-TYPE BASED TESTS FunEnglishwithme +99894 6333230
H. Both an iridium
anomaly and a fem spike appear in rocks at the end of the Triassic, too. That
accounts for the disappearing ichnotaxa: the creatures that made them did not survive the holocaust. The
surprise is how rapidly the new ichnotaxa appear.
I. Dr Olsen and his colleagues suggest that the explanation for this rapid increase in size may be a
phenomenon called ecological release. This is seen today when reptiles (which, in modem times, tend to be
small creatures) reach islands where they face no competitors. The most spectacular example is on the
Indonesian island of Komodo, where local lizards have grown so large that they are often referred to as
dragons. The dinosaurs, in other words, could flourish only when the competition had been knocked out.
J. That leaves the question of where the impact happened. No large hole in the earth's crust seems to
be 202m years old. It may, of course, have been overlooked. Old craters are eroded and buried, and not
always easy to find. Alternatively, it may have vanished. Although continental crust is more or less
permanent, the ocean floor is constantly recycled by the tectonic processes that bring about continental drift.
There is no ocean floor left that is more than 200m years old, so a crater that formed in the ocean would
have been swallowed up by now.
K. There is a third possibility, however. This is that the crater is known, but has been misdated. The
Manicouagan “structure”, a crater in Quebec, is thought to be 214m years old. It is huge—some 100km
across—and seems to be the largest of between three and five craters that formed within a few hours of each
other as the lumps of a disintegrated comet hit the earth one by one.
