- DI & DS
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Intelligence & CR
- Alphabet & Number Ranking
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- Average
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- Simple Equations
- Simple Interest and Compound Interest
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13.
The lithosphere, or outer shell, of the earth is made up of about a dozen rigid plates that move with respect to one another. New lithosphere is created at mid-ocean ridges by the upwelling and cooling of magma from the earth’s in terior. Since new lithosphere is continuously being created and the earth is not expanding to any appreciable extent, the question arises : What happens to the “old” lithosphere? The answer came in the late 1960s as the last major link in the theory of sea-floor spreading and plate tectonics that has revolutionized our understanding of tectonic processes, or structural deformations, in the earth and has provided a unifying theme for many diverse observations of the earth sciences. The old lithosphere is subducted, or pushed down, into the earth’s mantle (the thick shell of red-hot rock beneath the earth’s thin, cooler crust and above its metallic, partly melted core). As the formerly rigid plate descends, it slowly heats up, and over a period of millions of years it is absorbed into the general circulation of the earth’s mantle. The subduction of the lithosphere is perhaps the most significant phenomenon in global tectonics. Subduction not only explains what happens to old lithosphere but also accounts for many of the geologic processes that shape the earth’s surface. Most of the world’s volcanoes and earthquakes are associated with descending lithospheric plates. The prominent island arcs—chains of islands such as the Aleutians, the Kuriles, the Marianas, and the islands of Japan—are surface expressions of the subduction process. The deepest trenches of the world’s oceans, including the Java and Tonga trenches and all others associated with island arcs, mark the seaward boundary of subduction zones. Major mountain belts, such as the Andes and the Himalayas, have resulted from the convergence and subduction of lithospheric plates. To understand the subduction process it is necessary to look at the thermal regime of the earth. The temperatures within the earth at first increase rapidly with depth, reaching about 1,200 degrees Celsius at a depth of 100 kilometres. Then they increase more gradually, approaching 2,000 degrees C at about 500 kilometres. The minerals in peridotite, the major constituent of the upper mantle, start to melt at about 1,200 degrees C, or typically at a depth of 100 kilometres. Under the oceans the upper mantle is fairly soft and may contain some molten material at depths as shallow as 80 kilometres. The soft region of the mantle, over which the rigid lithospheric plate normally moves, is the asthenosphere. It appears that in certain areas convection currents in the asthenosphere may drive the plates, and that in other regions the plate motions may drive the convection currents. Several factors contribute to the heating of the lithosphere as it descends into the mantle. First, heat simply flows into the cooler lithosphere from the surrounding warmer mantle. Since the conductivity of the rock increases with temperature, the conductive heating becomes more efficient with increasing depth. Second as the lithospheric slab descends it is subjected to increasing pressure, which introduces heat of compression. Third, the slab is heated by the radioactive decay of uranium, thorium and potassium, which are present in the earth’s crust and add heat at a constant rate to the descending material. Fourth, heat is provided by the energy released when the minerals in the lithosphere change to denser phases, or more compact crystal structures, as they are subjected to higher pressures during descent. Finally, heat is generated by friction, shear stresses and the dissipation of viscous motions at the boundaries between the moving lithospheric plate and the surrounding mantle. Among all these sources the first and fourth contribute the most toward the heating of the descending lithosphere.
[1] Each of the following geological phenomena is mentioned in the passage as being relevant to the subduction of the lithosphere except:
(1) principal archipelagoes
(2) significant rifts in the sea bottom
(3) Expository
(4) prominent mountain ranges[2] The style of the passage can best be described as:
(1) Oratorical
(2) Argumentative
(3) expository
(4) Meditative[3] The author is most probably addressing which of the following audiences?
(1) Geothermal researchers investigating the asthenosphere as a potential energy source.
(2) Historians of science studying the origins of plate tectonic theory.
(3) College undergraduates enrolled in an introductory course on geology.
(4) Graduate students engaged in analyzing the rate of sea-floor spreading.[4] Which of the following is not true of the heating of the lithosphere as it is described in the passage?
(1) The temperature gradient between the lithosphere and the surrounding mantle enables heat to be transferred from the latter to the former.
(2) Minerals in the lithospheric slab release heat in the course of phase changes that occur during their descent into the mantle.
(3) The more the temperature of the lithospheric slab increases, the more conductive the rock itself becomes.
(4) The further the lithospheric slab descends into the mantle, the faster the radioactive decay of elements within it adds to its heat.
asked in MAT
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14.
The nature of financial integration of developing countries with developed countries has been radically transformed over the last four years. Evidence collated by the World Bank’s annual report for 2007 on global development finance reveal a number of features of the new scenario that have far-reaching implications. The first of these is an acceleration of financial flows to developing countries precisely during the years when as a group, they have seen rising surpluses on their current account. Total flows touched a record $ 571 billion in 2006, having risen by 19 per cent on top of an average growth of 40 per cent during the three previous years. Relative to the Gross Domestic Product (GDP) of these countries, total flows, at 5.1 per cent, are at levels that they touched at the time of the East Asian financial crisis in 1997. A second feature is the acceleration of the long-term tendency for private flows to dominate over official (bilateral and multilateral) flows. Private debt equity inflows, which had risen by 50 per cent a year over the three years ending 2005 increased by another 17 per cent in 2006 to touch a record $647 billion. On the other hand net official lending has in fact, declined over the past two years. One factor accounting for this is the failure of the Group of Seven (G-7) countries to match promises of a substantial hike in aid disbursements beyond what the retirement of the debt of few heavily indebted poor countries ensures. The other is that the more developed among developing countries have chosen to make advance repayments of debt owed to official creditors, especially the International Monetary Fund (IMF) and the World Bank. Overall, principal repayments to official creditors exceeded disbursements by $70 billion in 2005 and $ 75 billion in 2006. In the event, there has been a reverse flow of capital to the World Bank and the IMF which is threatening the viability and influence of these institutions, especially the latter. However, the increase in private flows has more than matched the reverse flows to official creditors. The third feature is that the dominance of private flows has meant that both equity and debt flows to developing countries has risen rapidly with the surge being greater in the case of the former. Net private debt and equity flows to developing countries have risen from a little less than $170 billion in 2002 to close to $647 billion in 2006, an almost fourfold increase over a four year period. While net private equity flows which rose from $163 billion to $419 billion, dominated the surge, net private debt flows too increased rapidly. Bond issues rose from $10.4 billion to $49.3 billion and borrowing from international banks increased from $2.3 billion to a huge $112.2 billion. What is more, net shortterm debt, outflows of which tend to trigger financial crises, has risen from around half a billion in 2002 to $72 billion in 2006. The fourth feature, which is a corollary of these developments, is that there is a high degree of concentration of flows to developing countries, implying excess exposure in a few countries. Ten countries (out of 135) accounted for 60 per cent of all borrowing during 2002-04 and that proportion has risen subsequently to touch three-fourths in 2006. In the portfolio equity market, flows to developing countries were directed at acquiring a share in equity either through the secondary market or by buying into Initial Public Offers (IPOs). IPOs dominated in 2006 accounting for $53 billion of the $96 billion in flow. But, here too, there were signs of concentration. Four of the 10 largest IPOs were by Chinese companies, accounting for twothirds of the total IPO value. Another three of those 10 were by Russian companies, accounting for an additional 22 per cent of the IPO value. A fifth feature is that despite this rapid rise in developing country exposure, with that exposure being excessively concentrated in a few countries, the market is still overtly optimistic. Ratings upgrades dominate downgrades in the bond market. And bond market spreads are at unusual lows. This optimism indicates that risk assessments are pro-cyclical, underestimating risk when investments are booming, and overestimating risks when markets turn downwards. But, there are two consequences : the herding of investors in developing country markets and their willingness to invest in a larger volume of money in risky unrated instruments. Finally, the rapid rise in capital flows to developing countries at a time when many of them are recording large current account surpluses has substantially increased their foreign exchange reserves and triggered an outflow of capital. This outflow takes three forms : (i) investment of reserves in safe and low return instruments such as United States Treasury Bills, (ii) financing of asset acquisition to support the growing presence of leading developing country firms in global commodity markets; and (iii) financial investments in and lending to other developing countries, resulting in the South-South flow of capital. These trends together suggest that developing countries are still largely restricted to the low return or high-risk segments of global capital flow. This is the cost they bear to meet the requirements of ensuring balance in the global balance of payments. These features of the current global financial scenario can be interpreted in two ways. One is in the direction taken by the world Bank. It admits, on the one hand, that “the probability of a turn in the credit cycle” has risen and that a “Key challenge facing developing countries is to manage the transition by taking pre-emptive measures aimed at lessening the risk of a sharp, unexpected reversal in capital flows”. On the other, it downplays the dangers involved by arguing that the surge in capital flows “speaks well for the resilience of developing economies and for the ability of international financial market to manage risks”. An alternative view would be that many emerging market economies that attract a disproportionate share of these capital flows are fast approaching a situation where they are vulnerable to financial crises with the current scenario incorporating features that could make these crises more intense. What is more, it appears that prudential norms, risk management techniques and disclosure requirements that have been put in place as part of the so-called “new international financial architecture” seem inadequate to foreclose a build-up of this kind. This is not surprising since garnering large and quick profits rather than minimising risks seems to be the dominant requirement of financial institutions from the developed countries. The current situation is the inevitable result of expanding the space for financial capital through dilution or elimination of regulation. Financial liberalisation has ensured that since the late 1970s, the newly discovered “emerging markets” among developing countries have been the new frontier for profiteering by global financial institutions. Awash with the liquidity derived from the surpluses earned by oil exporters and the saving accumulated by the generation of baby-boomers in the West, banks, investment funds and pension funds were looking to new avenues for lucrative investments. The role of financial intermediaries was one of dressing up developing countries that were hitherto “untouchables” as lucrative destinations for financial capital. And financial innovation consisted in not just identifying instruments that could carry such investments but derivatives that could help hedge against the risk associated with rushing into uncharted territory. The process began when developing countries were still reeling under the effects of declining non-fuel commodity prices and rising oil prices which had left gaping holes in the current account of their balance of payments. The new found interest of global finance offered developing country governments an opportunity to finance that gap, even if it meant offering high returns to foreign financial investors. It was this conflation of interests of developing country governments and financial institutions from the developed countries that led up to the debt crisis of the 1980s and the financial crisis of the 1990s, including those that began with the East Asian crisis in 1997. One consequence of the 1997 crisis was a sharp decline in lending to developing countries. But this did not mean a decline in capital flows. Rather, encouraged by the post-crisis deflation in asset prices in emerging markets and the sharp devaluation of their currencies, foreign direct investment kept flowing into developing countries to acquire assets at rock bottom prices when measured in hard currencies. While net debt flows to developing countries declined from $53.1 billion in 1998 to just $1.2 billion in 2000, net FDI flows remained more or less stable at around $170 billion a year. Since 2002 when growth accelerated or remained high in China and India and commodity prices rose sharply in the case of oil and metals and moderately in the case of agriculture, this lull in capital flows has given way to a surge. Besides the features noted above, three kinds of developments have accompanied this surge. First, the growing importance of unregulated hedge funds looking for abnormal returns in portfolio equity markets which renders activity in those markets highly speculative and opaque. Second, the rapid increase in investments by “private equity” firms investing largely in unlisted equity— in corporations in developing countries. The size of each of these investments is such that they identified as foreign “direct” investments, even though their objective is speculative. The evidence on the controversial role played by these firms in the developed countries indicates that their activity too is extremely opaque. Third, the revival once again of the global market for developing country debt, driven this time by private corporate borrowing in the syndicated loan market. Since this new surge in credit rides on a wave of securitisation that transfers the risk associated with such lending to pension and mutual funds among others, accumulating risk does not serve as a deterrent on banks creating such credit. There are a number of implications of these tendencies. To start with, the risk associated with the current surge in capital flows can be and is much greater than it was true during previous episodes involving a similar surge. Moreover, the surge is accompanied by the growing acquisition of assets in developing countries outside the stock market with objectives that are largely speculative so that a sell-off, if it occurs would be far more widespread. And the persistence of the herd instinct has meant that the surge in fixed and portfolio investment flows has resulted in a revival of credit flows that is unbridled since it is accompanied by risk-mitigation techniques that transfer risk to those who are least equipped to assess them. Unfortunately, all of this occurs in an environment in which the target of both investment and debt flows is the private sector which makes it difficult for governments that have liberalised financial regulation to control such flows. In sum, the risks associated with the current surge in capital flows are far greater than what emerges from the World Bank’s rather sanguine assessment of the possible fall-out of the ongoing transformation of global financial flows. A turn in the investment cycle, with far-reaching implications, is real and imminent.
[1] According to the passage, which one of the following statement(s) is/are true?
(1) The current situation is the inevitable result of expanding the space for financial capital through dilution or elimination of regulation.
(2) The role of financial intermediaries was one of dressing up developing countries that were hitherto untouchables as lucrative destinations for financial capital.
(3) The new found interest of global finance offered developing country governments an opportunity to finance that gap, even if it meant offering high returns to foreign financial investors.
(4) All of these[2] Total financial flows to developing countries reached a record $571 billion in ___, having risen by nineteen per cent on top of an average growth of ___ during the previous three years.
(1) 2005, 50%
(2) 2006, 40%
(3) 2004, 22%
(4) 2002, 60%[3] The rapid rise in capital flows to developing countries has substantially increased their foreign exchange reserves and triggered an outflow of capital in the form of:
(1) financial investments in and lending to other developing countries.
(2) financing of asset acquisition to support the growing presence of leading developing country firms in global commodity markets.
(3) investment of reserves in safe and low return instruments such as United States Treasury Bills.
(4) All of these[4] Ten developing countries out of one hundred and thirty five accounted for sixty per cent of all borrowing during 2002-2004 and that proportion has risen subsequently to touch ___ in 2006:
(1) sixty per cent
(2) fifty per cent
(3) seventy five per cent
(4) forty per centasked in MAT
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15.
At the Fourth World Water Forum held in Mexico City in March 2006, the 120-nation assembly could not reach a consensus on declaring the right to safe and clean drinking water a human right. Millions of people the world over do not have access to potable water supply. But it is good times for the bottled-water industry, which is cashing in on the need for clean drinking water and the ability of urban elite to pay an exorbitant price for this very basic human need. The fortunes of this more-than-$100-billion global industry are directly related to the human apathy towards the environment—the more we pollute our water bodies, the more the sales of bottled water. It is estimated that the global consumption of bottled water is nearing 200 billion liters—sufficient to satisfy the daily drinking water need of onefourth of the Indian population or about 4.5 per cent of the global population.
In India, the per capita bottled water consumption is still quite low—less than five liters a year as compared to the global average of 24 liters. However, the total annual bottled water consumption has risen rapidly in recent times—it has tripled between 1999 and 2004—from about 1.5 billion liters to five billion liters. These are boom times for the Indian bottled water industry—more so because the economics are sound, the bottom line is fat and the Indian government hardly cares for what happens to the nation’s water resources. India is the tenth largest bottled water consumer in the world. In 2002, the industry had an estimated turnover of Rs 10 billion (Rs 1,000 crores). Today it is one of India’s fastest growing industrial sectors. Between 1999 and 2004, the Indian bottled water market grew at a compound annual growth rate (CAGR) of 25 per cent—the highest in the world. With over a thousand bottled water producers, the Indian bottled water industry is big by even international standards. There are more than 200 brands, nearly 80 per cent of which are local. Most of the small-scale producers sell nonbranded products and serve small markets. In fact, making bottled water is today a cottage industry in the country. Leave alone the metros, where a bottled-water manufacturer can be found even in a one-room shop, in every medium and small city and even some prosperous rural areas there are bottled water manufacturers.
Despite the large number of small producers, this industry is dominated by the big players—Parle Bisleri, Coca-Cola, PepsiCo, Parle Agro, Mohan Meakins, SKN Breweries and so on. Parle was the first major Indian company to enter the bottled water market in the country when it introduced Bisleri in India 25 years ago. The rise of the Indian bottled water industry began with the economic liberalization process in 1991. The market was virtually stagnant until 1991, when the demand for bottled water was less than two million cases a year. However, since 1991-1992 it has not looked back, and the demand in 2004-05 was a staggering 82 million cases. Bottled water is sold in a variety of packages: pouches and glasses, 330 ml botles, 500 ml bottles, one-liter bottles and even 20 to 50 liter bulk water packs. The formal bottled water business in India can be divided broadly into three segments in tems of cost: premium natural mineral water, natural mineral water and packaged drinking water.
Attracted by the huge potential that India’s vast middle class offers, multinational players such as Coca-Cola and PepsiCo have been trying for the past decade to capture the Indian bottled water market. Today they have captured a significant portion of it. However, Parle Bisleri continues to hold 40 per cent of the market share. Kinley and Aquafina are fast catching up, with Kinley holding 20-25 per cent of the market and Aquafina approximately 10 per cent. The rest, including the smaller players, have 20-25 per cent of the market share.
The majority of the bottling plants whether they produce bottled water or soft drinks—are dependent on groundwater. They create huge water stress in the areas where they operate because groundwater is also the main source—in most places the only source—of drinking water in India. This has created huge conflict between the community and the bottling plants. Private companies in India can siphon out, exhaust and export groundwater free because the groundwater law in the counry is archaic and not in tune with the realities of modern capitalist societies. The existing law says that “the person who owns the land owns the groundwater beneath”. This means that, theoretically, a person can buy one square metre of land and take all the groundwater of the surrounding areas and the law of land cannot object to it. This law is the core of the conflict between the community and the companies and the major reason for making the business of bottled water in the country highly lucrative.[1] According to the passage, which one of the following statements is not true?
(1) Private companies are exploiting groundwater resources in India due to outdated law.
(2) The growth of Indian bottled water industry is a preeconomic liberalization process.
(3) Manufacturers excluding bigger players have approximately 20-25% of the market share of bottled water.
(4) Bottled water production in India is a cottage industry today.[2] Which brand is having the largest pie in the Indian bottled water market?
(1) Coca-Cola
(2) Parle Bisleri
(3) PepsiCo
(4) Mohan Meakins[3] What is/are the reason(s) for the global growth of bottled water industry?
(1) Pollution of water bodies
(2) Basic human need for clean drinking water
(3) Paying capacity of the elite
(4) All of the above[4] According to the passage, which of the following statements is/are true?
A. In India, the increase in total annual bottled water consumption is followed by increase in per capita bottled water consumption.
B. Indian bottled water market grew at the highest CAGR.
C. The formal bottled water business in India is divided into broadly two segments in terms of cost.
(1) A only
(2) A and C both
(3) B only
(4) A, B and Casked in MAT
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16.
Much as an electrical lamp transforms electrical energy into heat and light, the visual “apparatus” of a human being acts as a transformer of light into sight. Light projected from a source or reflected by an object enters the cornea and lens of the eyeball. The energy is transmitted to the retina of the eye whose rods and cones are activated. The stimuli are transferred by nerve cells to the optic nerve and then to the brain, man is a binocular animal, and the impressions from his two eyes are translated into sight—a rapid, compound analysis of the shape, form, colour, size, position, and motion of the things he sees. Photometry is the science of measuring light. The illuminating engineer and designer employ photometric data constantly in their work. In all fields of application of light and lighting, they predicate their choice of equipment, lamps, wall finishes, colours of light and backgrounds, and other factors affecting the luminous and environmental pattern to be secured, in great part from data supplied originally by photometric laboratory. Today, extensive tables and charts of photometric data are used widely, constituting the basis for many details of design. Although the lighting designer may not be called upon to the detailed work of making measurements or plotting data in the form of photometric curves and analyzing them, an understanding of the terms used and their derivation form valuable background knowledge. The perception of colour is a complex visual sensation, intimately related to light. The apparent colour of an object depends primarily upon four factors : its ability to reflect various colours of light, the nature of the light by which it is seen, the colour of its surroundings, and the characteristics and state of adaptation of the eye. In most discussions of colour, a distinction is made between white and coloured objects. White is the colour name most usually applied to a material that diffusely transmits a high percentage of all the hues of light. Colours that have no hue are termed neutral or achromatic colours. They include white, off-white, all shades of gray, down to black. All coloured objects selectively absorb certain wavelengths of light and reflect or transmit others in varying degrees. Inorganic materials, chiefly metals such as copper and brass, reflect light from their surfaces. Hence we have the term “surface” or “metallic” colours, as contrasted with “body” or “pigment” colours. In the former, the light reflected from the surface is often tinted. Most paints, on the other hand, have body or pigment colours. In these, light is reflected from the surface without much colour change, but the body material absorbs some colours and reflects others; hence, the diffuse reflection from the body of the material is coloured but often appears to be overlaid and diluted with a “white” reflection from the glossy surface of the paint film. In paints and enamels, the pigment particles, which are usually opaque, are suspended in a vehicle such as oil or plastic. The particles of a dye, on the other hand, are considerably finer and may be described as colouring matter in solution. The dye particles are more often transparent or translucent.
[1] According to the passage, lighting engineers need not:
(1) plot photometric curves
(2) utilize photometric data
(3) understand photometric techniques
(4) have mathematical expertise[2] The colour black is an example of:
(1) a surface colour
(2) an achromatic colour
(3) an organic colour
(4) a diffuse colour[3] Paint is an example of a substance containing:
(1) inorganic material
(2) body colours
(3) surface colours
(4) metallic colours[4] The perception of colour is:
(1) a photometric phenomenon
(2) a complex visual sensation
(3) activated by the brain
(4) light reflected by a sourceasked in MAT
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17.
It is indisputable that in order to fulfil its many functions, water should be clean and biologically valuable. The costs connected with the provision of biologically valuable water for food production, with the maintenance of sufficiently clean water, therefore, are primarily production costs. Purely “environmental” costs seem to be in this respect only costs connected with the safeguarding of cultural, recreational and sports functions which the water courses and reservoirs fulfil both in nature and in human settlements.
The pollution problems of the atmosphere resemble those of the water only partly. So far, the supply of air has not been deficient as was the case with water, and the dimensions of the air-shed are so vast that a number of people still hold the opinion that air need not be economized. However, scientific forecasts have shown that the time may be already approaching when clear and biologically valuable air will become problem No. 1.
Air being ubiquitous, people are particularly sensitive about any reduction in the quality of the atmosphere, the increased contents of dust and gaseous exhalations, and particularly about the presence of odours. The demand for purity of atmosphere, therefore, emanates much more from the population itself than from the specific sectors of the national economy affected by a polluted or even biologically aggressive atmosphere.
The households’ share in atmospheric pollution is far bigger than that of industry which, in turn, further complicates the economic problems of atmospheric purity. Some countries have already collected positive experience with the reconstruction of whole urban sectors on the basis of new heating appliances based on the combustion of solid fossil fuels; estimates of the economic consequences of such measures have also been put forward.
In contrast to water, where the maintenance of purity would seem primarily to be related to the costs of production and transport, a far higher proportion of the costs of maintaining the purity of the atmosphere derives from environmental consideration. Industrial sources of gaseous and dust emissions are well known and classified; their location can be accurately identified, which makes them controllable. With the exception, perhaps, of the elimination of sulphur dioxide, technical means and technological processes exist which can be used for the elimination of all excessive impurities of the air from the various emissions.
Atmospheric pollution caused by the private property of individuals (their dwellings, automobiles, etc.) is difficult to control. Some sources such as motor vehicles are very mobile, and they are thus capable of polluting vast territories. In this particular case, the cost of anti-pollution measures will have to be borne, to a considerable extent, by individuals, whether in the form of direct costs or indirectly in the form of taxes, dues, surcharges etc.
The problem of noise is a typical example of an environmental problem which cannot be solved only passively, i.e., merely by protective measures, but will require the adoption of active measures, i.e., direct interventions at the source. The costs of a complete protection against noise are so prohibitive as to make it unthinkable even in the economically most developed countries. At the same time it would not seem feasible, either economically or politically, to force the population to carry the costs of individual protection against noise, for example, by reinforcing the sound insulation of their homes. A solution of this problem probably cannot be found in the near future.[1] Scientific forecasts have shown that clear and biologically valuable air:
(1) is likely to remain abundant for some time
(2) may soon be dangerously lacking
(3) creates fewer economic difficulties than does water pollution
(4) may be beyond the capacity of our technology to protect[2] The costs involved in the maintenance of pure water are determined primarily by:
I. Production costs
II. Transport costs
III. Research costs
(1) I only
(2) I and II only
(3) III only
(4) II and III only
[3] According to the passage, the problem of noise can be solved through:
I. Active measures
II. Passive measures
III. Tax levies
(1) I only
(2) I and II only
(3) III only
(4) II and III only[4] According to the passage, the costs of some anti-pollution measures will have to be borne by individuals because:
(1) individuals contribute to the creation of population
(2) industry is not willing to bear its share
(3) governments do not have adequate resources
(4) individuals are more easily taxed than producersasked in MAT
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18.
The lithosphere, or outer shell, of the earth is made up of about a dozen rigid plates that move with respect to one another. New lithosphere is created at mid-ocean ridges by the upwelling and cooling of magma from the earth’s interior. Since new lithosphere is continuously being created and the earth is not expanding to any appreciable extent, the question arises: What happens to the “odd” lithosphere?
The answer came in the late 1960s as the last major link in the theory of sea-floor spreading and plate tectonics that has revolutionized our understanding of tectonic processes, or structural deformation, in the earth and has provided a unifying theme for many diverse observations of the earth sciences. The old lithosphere is subducted, or pushed down, into the earth’s mantle (the thick shell of red-hot rock beneath the earth’s thin, cooler crust and above its metallic, partly melted core). As the formerly rigid plate descends it slowly heats up, and over a period of millions of years it is absorbed into the general circulation of the earth’s mantle.
The subduction of the lithosphere is perhaps the most significant phenomenon in global tectonics. Subduction not only explains what happens to old lithosphere but also accounts for many of the geologic processes that shape the earth’s surface. Most of the world’s volcanoes and earthquakes are associated with descending lithospheric plates. The prominent island arcs—chains of islands such as the Aleutians, the Kuriles, the Marianas, and the islands of Japan—are surface expressions of the subduction process. The deepest trenches of the world’s oceans, including the Java and Tonga trenches and all others associated with island arcs, mark the seaward boundary of subduction zones. Major mountain belts, such as the Andes and the Himalayas, have resulted from the convergence and subduction of lithospheric plates.
To understand the subduction process it is necessary to look at the thermal regime of the earth. The temperatures within the earth at first increase rapidly with depth, reaching about 1,200 degrees Celsius at a depth of 100 kilometers. Then they increase more gradually, approaching 2,000 degrees C at about 500 kilometers. The minerals in peridotite, the major constituent of the upper mantle, start to melt at about 1,200 C, or typically at a depth of 100 kilometers. Under the oceans the upper mantle is fairly soft and may contain some molten material at depths as shallow as 80 kilometers. The soft region of the mantle, over which the rigid lithospheric plate normally moves, is the asthenosphere. It appears that in certain areas convection currents in the asthenosphere may drive the plates, and that in other regions the plate motions may drive the convection currents.
Several factors contribute to the heating of the lithosphere as it descends into the mantle. First, heat simply flows into the cooler lithosphere from the surrounding warmer mantle. Since the conductivity of the rock increases with temperature, the conductive heating becomes more efficient with increasing depth. Second, as the lithospheric slab descends it is subjected to increasing pressure, which introduces heat
of compression. Third, the slab is heated by the radioactive decay of uranium, thorium and potassium, which are present in the earth’s crust and add heat at a constant rate to the descending material. Fourth, heat is provided by the energy released when the minerals in the lithosphere change to denser phases, or more compact crystal structures, as they are subjected to higher pressures during descent. Finally, heat is generated by friction, shear stresses and the dissipation of viscous motions at the boundaries between the moving lithospheric plate and the surrounding mantle. Among all these sources the first and fourth contribute the most toward the heating of the descending lithosphere.[1] According to the passage, which of the following statements is/are true of the earth’s mantle?
I. It is in a state of flux.
II. Its temperature far exceeds that of the lithosphere.
III. It eventually incorporates the subducted lithosphere.
(1) I only
(2) I and III only
(3) II only
(4) I, II and III[2] It can be inferred from the passage that the author regards current knowledge about the relationship between lithosphere plate motions and the convection currents in the asthenosphere as:
(1) obsolete
(2) derivative
(3) unfounded
(4) tentative[3] The author is most probably addressing which of the following audiences?
(1) Geothermal researchers investigating the asthenosphere as a potential energy source
(2) College undergraduates enrolled in an introductory course on geology
(3) Historians of science studying the origins of plate tectonic theory
(4) Graduate students engaged in analyzing the rate of sea-floor spreading[4] Which of the following is not true of the heating of the lithosphere as it is described in the passage?
(1) The temperature gradient between the lithosphere and the surrounding mantle enables heat to be transferred from the latter to the former.
(2) The more the temperature of the lithospheric slab increases, the more conductive the rock itself becomes.
(3) Minerals in the lithospheric slab release heat in the course of phase changes that occur during their descent into the mantle.
(4) The further the lithospheric slab descends into the mantle, the faster the radioactive decay of elements within it adds to its heat.asked in MAT
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