Determining Past Climates
Paragraph 1: Glaciers form over land where temperatures are sufficientlylow so that, during the course of a year, more snow falls than melts. Successive snow accumulations over many years compactthe snow, which slowly recrystallizes into ice. Under the influence of gravity, the ice begins to move, and a glacier is formed. A mere 18,000 years ago, Earth was in the grip of a cold spell, with alpine glaciers extending down river valleys and continental glaciers covering vast areas of North America and Europe.The ice measured several kilometers thick and extended as far south as New York and the Ohio River Valley. Perhaps glaciers advanced ten times during the past two million years, only to retreat. In the warmer periods between glacier advances, average global temperatures were slightly higher than they are at present.
1. In mentioning temperatures that are “sufficiently” low, the author means temperatures that are
A. extremely low
B. low enough
C. low at times
D. always low
2. According to paragraph 1, which of the following does NOT correctly characterize glaciers?
A. They form over land.
B. They result when snow repeatedly melts and refreezes.
C. They move.
D. They accumulate snow over many years.
3. 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.
A. Just 18,000 years ago, glaciers covered large areas of North America and Europe.
B. A mere 18,000 years ago, vast areas of North America and Europe were in the grip of a cold spell.
C. Alpine glaciers once expanded outward from river valleys to cover most of continental Europe and North America.
D. During serious cold spells, glaciers covered not only alpine river valleys, but large portions of whole continents.
Paragraph 2: The geological evidence left behind by advancing and retreating is one factor suggesting that global climate has undergoneslow but continuous changes. To reconstruct past climates, scientists must examine and then carefully piece together all the available evidence. Unfortunately, the evidence only gives a general understanding of what the climate was like. For example, fossil pollen of a tundra plant collected in a layer of sediment in New England and dated to be 12,000 years old suggests that the climate of that region used to be much colder.
4. Why does the author mention “fossil pollen of a tundra plant collected in a layer of sediment in New England”?
A. To provide evidence that tundra plants have been in New England for much longer than previously thought
B. To support the claim that certain plants are resistant to slow but continuous climate change
C. To counter the claim that the New England climate was once much warmer than it is today
D. To illustrate how small bits of evidence can provide clues about past climates
Paragraph 3: Other evidence of global climatic change comes from core samples (taken by deep drilling) from ocean-floor sediments and ice from Greenland. Thousands of meters of ocean-floor sediment obtained with a hollow-centered drill were analyzed. The sediment contains the remains of calcium carbonate shells of organisms that once lived near the surface. Because certain organisms live within a narrow range of temperature, the distribution and type of organisms within the sediment indicate the surface-water temperature.
5. According to paragraph 3, analysis of core samples from ocean floor sediments provides information about
A. how much calcium carbonate is in the sediment
B. the thickness of the ice between layers of sediment
C. the surface temperature of the ocean at the time the sediments were deposited
D. the distribution and type of sediment that was deposited at various temperatures
Paragraph 4: In addition, the oxygen-isotope ratio of these shells provides information about the sequence of glacier advances. For example, most of the oxygen in seawater has an atomic weight of 16 because its nucleus contains eight protons and eight neutrons. However, about 1 out of every 1,000 oxygen atoms contains an extra two neutrons, giving it an atomic weight of 18. When ocean water evaporates, the heavier oxygen 18 tends to be left behind. In periods of cold, the evaporated water, rich in oxygen 16, falls as snow and becomes part of growing glaciers rather than returning to the oceans. Consequently, during periods of glacier advance, the oceans have less water and a higher concentration of oxygen 18. Since the shells of marine organisms are constructed from the oxygen atoms existing in ocean water, determining the ratio of oxygen 18 to oxygen 16 within these shells yields information about how the climate may have varied in the past. A higher ratio of oxygen 18 to oxygen 16 in the sediment record suggests a colder climate, while a lower ratio suggests a warmer climate. Using data such as these, scientists have been able to reconstruct Earth’s ocean surface temperatures.
6. According to paragraph 4, why does the concentration of oxygen 18 in shells of marine organisms indicate the water temperature when the shells were formed?
A. Since less seawater evaporates when the temperature of seawater falls, the concentration of oxygen 18 in seawater decreases during cold spells.
B. During cold periods, evaporated seawater that is rich in oxygen 16 becomes trapped as snow, leaving the remaining seawater richer in oxygen 18.
C. When the seawater is cold, it is difficult for marine organisms to form shells with water that incorporates oxygen 16, so their shells are formed using mainly oxygen 18.
D. When the seawater is warm, most of the oxygen in the seawater is rich in oxygen 16, but when the water becomes cold, most of the water with oxygen 16 evaporates.
Paragraph 5: Vertical ice cores extracted from glaciers in Antarctica and Greenland provide additional information on past temperature patterns. Since ice is composed of hydrogen and oxygen, examining the oxygen-isotope ratio in ancient cores provides a past record of temperature trends. Generally, the colder the air when the snow fell, the richer the concentration of oxygen 16 in the core. Moreover, bubbles of ancient air trapped in the ice can be analyzed to determine the past composition of the atmosphere.
7. Why does the author provide the information that “Generally, the colder the air when the snow fell, the richer the concentration of oxygen 16 in the core”?
A. To provide the principle that allows scientists to use ice cores to infer patterns of past temperatures
B. To explain why bubbles of air trapped in ice cores provide additional information about the composition of the atmosphere at the time the gas was trapped
C. To argue that when the air is warm, the concentration of oxygen 18 in an ice core is less than that of oxygen 16
D. To imply that water that contains oxygen 16 forms ice more readily than water that contains oxygen 18
Paragraph 6: Still other evidence of climatic change comes from dendrochronology, the study of annual growth rings of trees. As a tree grows, it produces a layer of wood cells under its bark. Each year’s growth appears as a ring. The changes in thickness of the rings may indicate climatic changes that have taken place from one year to the next. Tree rings are only useful in regions that experience an annual weather cycle and in trees that are stressed by temperature or moisture during their growing season. The growth of tree rings has been correlated with precipitation and temperature patterns for hundreds of years into the past in various regions of the world.
8. It can be inferred from paragraph 6 that dendrochronology is probably NOT useful for evaluating climate change in
A. areas that are sometimes subject to very hot summers
B. consistently warm equatorial regions
C. places that experience distinct seasons
D. forests that experience excessive moisture when winter snows melt
Paragraph 6: Still other evidence of climatic change comes from dendrochronology, the study of annual growth rings of trees. As a tree grows, it produces a layer of wood cells under its bark. Each year’s growth appears as a ring. ■The changes in thickness of the rings may indicate climatic changes that have taken place from one year to the next. ■Tree rings are only useful in regions that experience an annual weather cycle and in trees that are stressed by temperature or moisture during their growing season. ■The growth of tree rings has been correlated with precipitation and temperature patterns for hundreds of years into the past in various regions of the world.■
9. Look at the four squares [■] that indicate where the following sentence could be added to the passage. Where would the sentence best fit?
Without these conditions being met, there may be variations in tree ring thickness due to such factors as disease or predation, but the variations will not systematically reflect variations in climate.
10. Directions : An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the 3 answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
To construct past climates, scientists must examine and then carefully piece together all the available evidence.
Answer Choices
A. One indication that global temperatures have been falling over the past 2 million years is that glaciers have grown steadily in size through most of this period.
B. Geological evidence of the extensive advance and subsequent retreat of glaciers, as many as ten times in the last 2 million years, indicates global climate changes.
C. The quantity of air bubbles in a glacier can indicate how quickly it formed, and the level of oxygen 16 indicates whether the glacier first formed over land or over the ocean.
D. Since marine organisms form shells less readily in colder ocean waters, core samples of sediment with a lower quantity of shells indicate a colder climate period.
E. The concentrations of oxygen 18 in the shells of marine organisms and in core samples of glacial ice provide clues about past ocean levels and temperatures.
F. Fossil pollen, oxygen-isotope ratios in ancient glaciers, and the annual growth of tree rings can provide evidence about temperature and precipitation in the past.
答案请付费后查阅：
