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The extinction of the dinosaurs – thought to be caused by an asteroid

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The extinction of the dinosaurs – thought to be caused by an asteroid  [#permalink]

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New post 21 Jan 2020, 19:21
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The extinction of the dinosaurs – thought to be caused by an asteroid impact some 65 million years ago – was more likely to have been caused by a 'mantle plume' – a huge volcanic eruption from deep within the earth's mantle, the region between the crust and the core of the earth. This theory, already supported by a significant body of geologists and palaeontologists, is strengthened by new evidence.

Research by an American earth scientist, Professor Gerta Keller and her team, suggests that a similar eruption under the Indian Ocean several million years before the extinction of the dinosaurs had a similarly devastating impact on the environment. However, at this earlier time there is no evidence of any asteroid impact. Her findings are based on analysis of microfossil assemblages, which were found inside cores that had been drilled deep into sediments on the ocean floor.

The eruptions that were responsible for these two extinction events were as a result of mantle plumes – a phenomenon caused by the hot mantle rising from deep within the earth. Likened to the actions of a lava lamp, the mantle's heat causes it to rise and mushroom out; it then flattens causing the mantle to melt and spew magma over the earth's surface and across an area of some 1,000 kilometres diameter. These eruptions last between one and two million years and more than one million cubic kilometres of lava can be erupted in that time. Today, we can witness seven huge remnants of such mantle plume activity. These are also known as 'hotspots' and are responsible for the volcanic activity on Iceland, the islands of Hawaii, Easter, Reunion, Tristan and Louisville as well as volcanism in the Afar region of Ethopia.

According to Dr. Andrew Kerr of Cardiff University's School of Earth, Ocean and Planetary Sciences, mantle plumes are a catalyst for the formation of ocean basins and the fundamental reshaping of the earth's surfaces. The massive outpouring of lava, ashes, and gas can have significant effects on climate and have the potential to dictate the course of evolution. Kerr says that it is likely that were it not for mantle plumes, mammals would not have become predominant, and humankind would not be here today. Bizarrely, however, there is a vocal minority of earth scientists who do not believe that mantle plumes exist.


1. What is the central theme of the passage?

A. The role of mantle plumes in the extinction of dinosaurs
B. Unanticipated effects of mantle plume activity
C. Earth science theories that explain the extinction of dinosaurs
D. The formation and consequences of mantle plumes
E. Contrasting views of earth scientists on the mantle plume phenomenon



2. The author mentions ‘two extinction events’ in line 11 most probably in order to

A. support Dr. Kerr’s view that mantle plumes have a significant effect on the course of evolution, especially the predominance of mammals and the origin of humankind
B. undermine the evidence offered by Professor Keller’s study of mantle plume eruptions
C. highlight the devastating effects that mantle plume activities can have on the earth’s environment
D. question the assertion that mantle plumes were responsible for the eruptions that caused devastating environmental impact
E. strengthen the theory that asteroid impact was not the primary reason for the extinction of species in the past



3. According to the passage, each of the following statements about mantle plume activity is true, EXCEPT:

A. It is caused due to the heat from the earth’s mantle bubbling up, similar to the functioning of a lava lamp
B. During mantle plume eruptions, magma is spewed over hundreds of kilometres on the earth’s surface
C. Several ‘hotspots’ of volcanic activity across the globe give rise to mantle plume eruptions
D. It is an eruption that originates between the earth’s crust and its core and lasts for one or two million years
E. The massive deluge of lava, ashes, and gas during mantle plume eruptions can have significant effects on climate and evolution



4. It can be inferred from the passage that Professor Keller and team would be most likely to agree that which of the following is a possible outcome of mantle plume activity

A. The extinction of a species other than dinosaurs
B. The asteroid impact that happened 65 million years ago
C. The formation of microfossil assemblages on the ocean floor
D. The fundamental reshaping of the earth’s surface
E. The recent bouts of volcanic activity that the earth’s ‘hotspots’ have seen


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Re: The extinction of the dinosaurs – thought to be caused by an asteroid  [#permalink]

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New post 24 Jan 2020, 20:43
Official answers:
1.OA: D
The focus is on mantle plumes and not on dinosaurs – dinosaur extinction is only one of the several outcomes of mantle plumes. So, A and C are incorrect. The central theme is not the diverse views of earth scientists – for one, both views expressed (Kerr and Keller) are similar, not contrasting; there is only a mention that a different set of views exist. So E is also incorrect. Option B mentions 'unanticipated' – the passage makes no mention of whether the outcomes were surprising – so B is also incorrect.

2.OA: E
According to the passage, there were 2 extinction events. In the first case, there was no evidence of asteroid impact. The second is thought to be caused by asteroid impact. But the effects of both were similar. Dr. Kerr identifies that the cause of both was mantle plume activity and not asteroid impact. Thus, the author mentions this fact to support Professor Keller's finding – i.e. asteroid impact was probably not the primary reason for extinction of dinosaurs. Option A is wrong as it refers to Dr. Kerr – no relation. B is wrong as the author does not undermine Keller's study. Option C is wrong as this fact does not really help to highlight the devastating effects of mantle plumes – it just tells us that 2 events happened; nothing about their impact or intensity. Option D is incorrect as the author never questions the theory that mantle plumes caused the eruptions.

3.OA: C
This is an EXCEPT question. So we need to eliminate every answer choice that is mentioned in the passage. Option A (lines 12-13), B (lines 14-15), D (line 3 and line 15) and E (lines 22-23). However, the opposite of option C is mentioned in lines 16 to 18 – mantle plume activity is responsible for volcanic hotspots and vice versa.

4.OA: A
Since two extinction events with similar devastating effects are mentioned (lines 6 to 8), we can infer that a species apart from dinosaurs could have become extinct in the first eruption that occurred several million years before the extinction of dinosaurs. This is why option A is right. In option B, we DKCS anything about what caused the asteroid impact. In option C, the microfossil assemblages were studied by Prof Keller – but we DKCS if mantle plume activity caused the formation of these. Option D mentions a viewpoint of Dr. Kerr – we DKCS if Prof Keller would agree with this. Option E mentions 'recent volcanic activity' – we DKCS whether mantle plume activity caused this.
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Re: The extinction of the dinosaurs – thought to be caused by an asteroid   [#permalink] 24 Jan 2020, 20:43
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