The Dinosaurs Footprints and Extinction
A
Everybody knows that the dinosaurs were killed by an asteroid.
Something big hit the earth 65 million years ago and, when the dust had fallen, so had the great reptiles.
There is thus a nice if ironic, symmetry in the idea that a similar impact brought about the dinosaurs’ rise.
That is the thesis proposed by Paul Olsen, of Columbia University, and his colleagues in this week’s Science.
B
Dinosaurs first appeared in the fossil record 230m years ago, during the Triassic period.
But they were mostly small, and they shared the earth with lots of other sorts of reptile.
It was in the subsequent Jurassic, which began 202 million years ago, that they overran the planet and turned into the monsters depicted in the book and movie “Jurassic Park”.
(Actually, though, the dinosaurs that appeared on screen were from the still more recent Cretaceous period.)
Dr Olsen and his colleagues are not the first to suggest that the dinosaurs inherited the earth as the result of an asteroid strike.
But they are the first to show that the takeover did, indeed, happen in a geological eyeblink.
C
Dinosaur skeletons are rare.
Dinosaur footprints are, however, surprisingly abundant.
And the sizes of the prints are as good an indication of the sizes of the beasts as are the skeletons themselves.
Dr Olsen and his colleagues, therefore, concentrated on prints, not bones.
D
The prints in question were made in eastern North America, a part of the world then full of rift valleys similar to those in East Africa today.
Like the modern African rift valleys, the Triassic/Jurassic American ones contained lakes, and these lakes grew and shrank at regular intervals because of climatic changes caused by periodic shifts in the earth’s orbit.
(A similar phenomenon is responsible for modern ice ages.)
That regularity, combined with reversals in the earth’s magnetic field, which are detectable in the tiny fields of certain magnetic minerals, means that rocks from this place and period can be dated to within a few thousand years.
As a bonus, squishy lake-edge sediments are just the things for recording the tracks of passing animals.
By dividing the labour between themselves, the ten authors of the paper were able to study such tracks at 80 sites.
E
The researchers looked at 18 so-called ichnotaxa.
These are recognizable types of the footprint that cannot be matched precisely with the species of animal that left them.
But they can be matched with a general sort of animal, and thus act as an indicator of the fate of that group, even when there are no bones to tell the story.
Five of the ichnotaxa disappear before the end of the Triassic, and four march confidently across the boundary into the Jurassic.
Six, however, vanish at the boundary, or only just splutter across it; and three appear from nowhere, almost as soon as the Jurassic begins.
F
That boundary itself is suggestive.
The first geological indication of the impact that killed the dinosaurs was an unusually high level of iridium in rocks at the end of the Cretaceous when the beasts disappear from the fossil record.
Iridium is normally rare at the earth’s surface, but it is more abundant in meteorites.
When people began to believe the impact theory, they started looking for other Cretaceous-end anomalies.
One that turned up was a surprising abundance of fern spores in rocks just above the boundary layer - a phenomenon known as a “fern spike”.
G
That matched the theory nicely.
Many modern ferns are opportunists.
They cannot compete against plants with leaves, but if a piece of land is cleared by, say, a volcanic eruption, they are often the first things to set up shop there.
An asteroid strike would have scoured much of the earth of its vegetable cover, and provided a paradise for ferns.
A fern spike in the rocks is thus a good indication that something terrible has happened.
H
Both an iridium anomaly and a fern 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 modern 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 the 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.
Questions1 - 6
Do the following statements agree with the information given in the Reading Passage?
Choose the correct answer
YES if the statement is true
NO if the statement is false
NOT GIVEN if the information is not given in the passage
- Dr Paul Olsen and his colleagues believe that asteroid knock may also lead to dinosaurs’ boom.
-
YES
-
NO
-
NOT GIVEN
题解
查看题干，首先找到原因 asteroid knock，导致的事件是dinosaurs’ boom。阅读原文，开篇说的是Everybody knows，但是雅思里面很多阅读文章的观点与普罗大众的观点是相反的。并且在文章中出现了ironic, symmetry in the idea，这类表示否定意义的词语。然后还明确写出了dinosaurs’ rise，所以答案应该是Yes- Books and movie like Jurassic Park often exaggerate the size of the dinosaurs.
-
YES
-
NO
-
NOT GIVEN
题解
出现了专有名词Jurassic Park，然后行为是exaggerate，对象是size。阅读原文，确实找到了对应的专有名词，但是却并未发现相关描述size，也未发现有比较级或者夸大字眼，所以看下一题。- Dinosaur footprints are more adequate than dinosaur skeletons.
-
YES
-
NO
-
NOT GIVEN
题解
题干非常明显，对比footprints与skeletons，然后认为前者more adequate than后者。原文C段中非常详细地写了skeletons rare，然后footprints abundant，所以选YES，并且可以确定上一题答案是NOT GIVEN。- The prints were chosen by Dr Olsen to study because they are more detectable than the earth magnetic field to track the date of geological precise within thousands of years.
-
YES
-
NO
-
NOT GIVEN
题解
题干出现了比较级，比较的对象是prints和the earth magnetic field。文章中确实出现了球磁场的逆转，以及这两者可以被检测出来，但是并没有出现相关的比较形式，所以看下一题。- Ichnotaxa showed that footprints of dinosaurs offer exact information of the trace left by an individual species.
-
YES
-
NO
-
NOT GIVEN
题解
首先出现了一个专有名词Ichnotaxa，对象是footprints，动作是offer exact information，并且是individual species。在E段明确说明了cannot be matched precisely with the species of animal，所以答案是NO。并且可以得知，上一题的答案是NOT GIVEN- can find more Iridium in the earth’s surface than in meteorites.
-
YES
-
NO
-
NOT GIVEN
题解
首先是出现了比较级more...than，其次比较的对象是earth’s surface和meteorites，比较的东西是Iridium。F段中出现了答案Iridium is normally rare at the earth’s surface, but it is more abundant in meteorites，所以选NO。Questions7 - 13
Complete the following summary of the paragraphs of the Reading Passage
Using NO MORE THAN TWO WORDS from the Reading Passage for each answer.
Write your answers in gaps 7-13.
Dr Olsen and his colleagues applied a phenomenon named 7 to explain the large size of the Eubrontes, which is a similar case to that nowadays reptiles invade a place where there are no 8; for example, on an island called Komodo, indigenous huge lizards grow so big that people even regarding them as 9.
第7题
首先可以注意到空处前的单词是named，那么根据语义，该空应该填一个名词，它是Dr Olsen and his colleagues用来给某一种phenomenon取的名字。然后这个名字它是用来explain large size，并且这里出现了一个专有名词Eubrontes。在原文中可以找到这一句explanation for this rapid increase in size may be a phenomenon called ecological release，基本上和题干语意重合，其中rapid increase in size对应large size，phenomenon属于原词重现，named对应called。所以答案应该是ecological release。（值得一提的是Eubrontes这个词在文章中并没有直接出现，所以考试中不能硬着头去找专有名词）第8题
这个空紧接着第7题，如果是P3，那我觉着对应出题句在原文中可能不挨着，但是这是P1。题干中出现了reptiles invade和no，并且还有一个超高频考点similar to。回到原文，在I段中today直接对应nowadays，然后reptiles原词重现，并且还有一个no，所以答案呼之欲出，就是competitors。第9题
出现专用名词Komodo，还有lizards太big，然后空处就是需要填这个称呼。第I段中，直接定位到Komodo，然后large对应big，特别是so...that居然原词复现了。referred to as对应regarding them as，那么答案就是dragons。However, there were no old impact trace being found? The answer may be that we have 10 the evidence. Old craters are difficult to spot or it probably 11. Due to the effect of the earth moving. Even a crater formed in Ocean had been 12 under the impact of crust movement. Besides, the third hypothesis is that the potential evidence – some craters may be 13.
