2018年10月13日托福阅读真题+题目+答案：Sequencing Ice Ages

2018年10月13日托福阅读真题+题目+答案：Sequencing Ice Ages

Traditionally, climate scientists believed that Earth underwent four major periods of glaciation (being covered by ice sheets) with warm interglacials in between.But climate research has now shown that over the past 800,000 years Earth has seen a complex pattern of some twenty major climatic shifts, with temperatures alternating between very warm and intensely cold, featuring warm seas in northern Europe at one extreme and ice sheets covering vast areas of the globe at the other. The cause of these fluctuations lies in the complex relationship between Earth and the Sun. We are all familiar with the fact that Earth orbits the Sun and that it spins around its own axis, which is at an angle to the plane of its orbit. This causes some parts of Earth's surface to be nearer the Sun for periods of time, accounting for the differences between summer and winter.⬛ If all parts of this system were stable. Earth's climate would remain constant, but this is not so. ⬛ First, Earth's or bit is not perfectly circular but is slightly elliptical, causing a variation on a 100,000-year cycle. ⬛Secondly, the axis of Earth Changes its tilt angle by  a fraction over a .41,000-year cycle; and thirdly, the planet has a slight wobble (shaking movement) about its axis as it spins, setting up changes over a cycle of 23,000 years. ⬛ The combination of all these factors (known as the Milankovitch cycles) creates very small changes in the Sun-Earth relationship that determine the expansion or contraction of the polar ice cap and thus the sequence of fluctuating ice ages.

1.Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

O Earth's climate has now been shown to have had a complex pattern over the last 800.000 years of about twenty climate shifts between extremes of warm and cold

O The vast areas of the globe that were Once covered by ice sheets but are now warm seas are evidence of a climate shift that occurred 800,000 years ago

O Earth experienced a climate pattern that began 800,000 years ago and was marked by warm seas in northern Europe at the same time that vast ice sheets covered other areas. 

O Climate research shows that some locations such as northern Europe experienced more frequent alternations in temperatures over the past 800.000 years than other areas of the globe

2.According to paragraph 1, what would be the result if Earth's orbit and the angle of its axis were stable?

O Seasons would be milder and have warmer temperatures.

O Some parts of Earth's surface would be nearer the Sun for longer periods of time

O Major changes in Earth's weather patterns over long periods of time, such as the changes from glacial to nonglacial periods would not occur.

O Earth's orbit would be somewhat more elliptical .

The complexity of these changes has taken some time to unravel. The earliest work was done on glaciers in the Alpine region, and it was here that the four major stages of glaciation were identified, providing a useful regional sequence. More recently, over the last fifty years or so, work on deep-sea cores has pioneered a new way to study the phenomenon globally. The principle is quite simple: Deep-sea cores provide stratified sequences of accumulations of calcium carbonate derived from the shells of dead organisms. The calcium carbonate in these layers contains two different oxygen isotopes (oxygen of different atomic weights), 160 and 180, which the organisms extract from the atmosphere. Since it can be shown that cold conditions favor 180 over 160, by assessing the ratio of the two it is possible to arrive at a direct measurement relating to the temperature of the ocean at the time of deposition. From these measurements a system of twenty phases, known as marine isotope stages, can be distinguished, reflecting changes in Earth's climate. The method was extremely valuable in providing a relative sequence, but it needed to be calibrated to give approximate dates for the phases.

3.It can be inferred from paragraph 2 that using deep-sea cores to study major shifts in Earth's climate made which of the following possible?

O The discovery that the ocean was so Cold during some periods that it caused widespread death among shelled organism

O The recognition that glaciers covering Alpine regions contained considerably more 180 than was previously thought

O The ability to determine sequences of alternating warm and cold periods on a global scale

O The understanding that identifying regional sequences of climate was less useful than scientists once believed

4.According to paragraph 2, which of the following can be learned from the ratio of 160 to 180 in a given layer of a deep-sea core?

O How cold the surrounding ocean was at the time that the layer was deposited

O When calcium carbonate was deposited on the seafloor

O Which organisms were living at the time that the layer was deposited

O How many organisms died during phases of glaciation

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