In a discovery with frightening implications for human’s dominance of the Earth, scientists have discovered that a massive comet or asteroid, similar to the one that killed off thedinosaurs, wiped out the giant reptile’s predecessors about 200 million years earlier. The finding suggests that regular collisions between our planet and large objects act as an evolutionary dice-shaker. They send dominant species back to the starting square and advance other species to a dominant position. We could be next.
Students of the fossil record have long wondered about the greatest catastrophe ever to strike life on Earth, which they call ‘The Great Dying’. This happened 251 million years ago, when suddenly 90% of all marine animals and 70% of land vertebrates perished. The impact of a comet or asteroid similar to that which brought doom to the dinosaurs 65 million years ago was suspected. However, the latest edition of the journal Science reports on the first evidence that such a collision actually happened. Scientists at the Universities of Washington and Rochester in the US have found that molecules of helium and argon gas, which have been locked in since ‘The Great Dying’ are present in such proportions that they must have come from space. As in the later impact, the strike came from a body between 6 and 12 kilometres wide. Researcher Robert Poreda said yesterday the effect would have been to release energy one million times greater than the biggest earthquake of the past century. The crash coincided with volcanic activity on an unimaginable scale in what is now Siberia. Over a million years – a relatively short time in geological terms – 1.6 million cubic kilometres of lava poured out of the ground, covering the entire planet in a layer ten metres thick. Said Robert Poreda, ‘We’re not sure of all the environmental consequences but with the impact and the volcanic activity, we do know that Earth was not a happy place. It may be that the combined effects of impact and volcanism are necessary to cause such a tremendous extinction.’
The end of the dinosaurs also coincided with an eruption of lava from below the Earth’s crust, in what is now India. In both cases, the impact of the comet or asteroid may have caused the eruption. The dinosaur-killing impact has been tied to a crater on the Yucatan peninsula in Mexico, but it is not known where the earlier collision happened. At the time all the Earth’s land made up a single continent, Pangea. The age immediately prior to the dinosaurs was called the Permian. Although there were reptiles living in land and water (earlier versions of the dinosaurs), the dominant life form was the trilobite. This creature is visually somewhere between the woodlouse and the armadillo. At their peak, there were 15,000 kinds of trilobite. Around the time of the impact they disappeared. Something similar happened to the dinosaurs 65 million years ago. In the same way that the earlier impact seems to have cleared the way for them, the later crash made room for our ancestors, the mammals. ‘The two extinctions are like bookends for the age of the dinosaurs’, said Dr Peroda. ‘The first boundary helped the dinosaurs to establish themselves and the second extinguished it.’ Although it is likely to be millions of years before the next big asteroid or comet impact, there is a growing call for a defence system to be put in place.
8 Scientists have discovered that a huge comet or asteroid wiped out
A the dinosaurs.
B giant reptiles.
C creatures before the dinosaurs.
D creatures similar to the dinosaurs.
9 The ‘Great Dying’ happened
A 200 million years ago.
B 251 million years ago.
C 65 million years ago.
D 265 million years ago.
10 The ‘Great Dying’ killed
A a few land vertebrates.
B all the dinosaurs.
C most marine animals.
D some mammals.
11 Which statement is not true of the asteroid or comet?
A It was under 12 kilometres in diameter.
B It contained helium and argon.
C It contained lava.
D It was over six kilometres in diameter.
12 Where did the first massive comet or asteroid hit the earth?
A it is not known
B in Siberia
C in India
D in Mexico
13 Which statement is not true of the lava that covered the planet?
A It was caused by the impact of the asteroid.
B It was 1.6 cubic kilometres in volume.
C It was ten metres thick.
D It happened over one million years.
14 Which creatures lived at the same time as the trilobites?
15 According to the article, which of the following statements is true?
A There will be another giant asteroid.
B There is unlikely to be another ever.
C Humans will dominate the earth.
D It is time to expect another asteroid.