Recent concern over the warming effects of the rising amounts of the greenhouse gas carbon dioxide in the atmosphere has led scientists to investigate Earth’s climate history. It is now accepted that long-term changes in the Earth’s climate over billions of years are the result of variations in Earth’s orbit and the tilt of its rotational axis, and these factors produce fairly well-defined cycles of climate, with ice ages in the cold periods. One of the most recent glacial periods (ice ages) started about 30 million years ago; by 700,000 years ago the ice sheets reached what is now the United States mainland, thereafter advancing and receding approximately once every100.000 years.
However, geologists have found evidence for only a few other glacial epochs in the last billion years of Earth history- -one in the Permo-Carboniferous period about 250-350 million years ago, one in the Siluro-Devonian period about 410 million years ago, one in the Ordovician period about 440 million years ago, and one in the late Precambrian about 700 million years ago. Thus, for most of the last billion years, Earth’s climate has been relatively warm. It seems likely that orbital variations are not alone responsible for an ice age but that a trigger (stimulus) of some kind is also needed. One possibility is that higher albedo (overall reflectivity) due to increased cloud cover triggered temperature declines. ▉A more plausible trigger appears to be the latitudinal distribution of the continents. ▉At the present time, Antarctica is situated over the South Pole, and the North Pole is partly surrounded by Greenland, northern Canada, and northern Asia. ▉In the Permo-Carboniferous period, most landmasses were joined together in a supercontinent called Pangaea that was centered over the equator. ▉Nevertheless, parts of the continent (those areas containing portions of present-day South America, Antarctica, southern Africa, and India) extended to the South Pole. The circulation of ocean water near the poles was thereby impeded, and the water could not act to moderate temperature.
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.
A.Earth’s climate has undergone various changes over billions of years, with ice ages occurring in the colder periods.
B.lt is now believed that a number of lng-em changes in Earth’s orbit and in the tit of ts rational axis took place during ice ages.
C.Variations in Earth’s or it and in the tit of its rational axis cause lng-em climate changes, including periodic ice ages.
D.Extreme cold weather is a result of variations in Earth’s orbit and generally lasts for billions of years.
2.According to paragraph 2, which of the following best describes Earth’s climate over the past billion years?
A.Generally warm temperatures interrupted by several cold periods
B.Rapidly increasing temperatures with very brief cold periods
C.Long glacial periods with shorter periods of warm temperatures
D.Generally cool temperatures with a few glacial epochs
3.Paragraph 2 provides an answer to which of the following questions?
A.What can cause variation in Earth’s orbit?
B.What can cause Earth’s cloud cover to increase?
C.Which continent experienced the greatest temperature decrease during the Permo-Carboniferous glacial period?
D.D.Where were the continents situated during the Permo-Carboniferous period?
4.According to paragraph 2, the Permo-Carboniferous glacial period was most probably triggered by
A.high overall reflectivity caused by increased cloud cover
B.the gradual separation of landmasses joined together near the equator
C.the fact that ocean water could not circulate freely near the poles.
D.the centering of several continents over the South Pole
However, a different situation may have existed in the late Precambrian sometime between 800 and 600 million years ago. The continents were relatively small, separated, and near the equator. Harvard University geologists Paul F. Hoffman and Daniel P. Schrag suggested that this situation created more rainfall that cleaned carbon dioxide out of the air. The diminishment of this greenhouse gas lowered the global temperature sufficiently to allow the oceans to freeze over nearty completely, perhaps leaving only a narrow ice-free oceanic belt along the equator. This global glaciation event was termed “Snowball Earth” by geobiologist Joseph L. Kirschvink of the alfomia Institute of Technology. Earth thawed (unfroze) only after about 10 million years, when volcanic emissions (mainly from undersea volcanoes) had increased the concentration of carbon dioxide by 1,000 times over current levels. Carbon dioxide was able to achieve such high levels because of the near absence of rainfall in a world covered with ice. After the ice melted, global temperatures soared until rainfall was able to rid the atmosphere of most of the carbon dioxide.
5.The word “soared” in the passage is closest in meaning to
A.became unpleasant
B.increased dramatically
C.changed repeatedly
D.fell gradually
6.According to paragraph 3, which of the following was a factor leading to the glaciation event known as“Snowball Earth”?
A.The presence of a narrow ice-free ocean belt along the equator on some parts of Earth
B.The diminishment of carbon dioxide in the atmosphere
C.The absence of rainfall
D.Emissions from undersea volcanoes
7.According to paragraph 3, there was a large increase in global temperatures following the end of “Snowball Earth” because
A.an ice-free oceanic belt formed on some parts of Earth
B.melting ice released additional carbon dioxide into the atmosphere
C.there was little rainfall to wash away the carbon dioxide in the atmosphere
D.this glacial period was relatively short, lasting only 10 million years
Another variable that apparently affects global temperature is a minor variation in solar activity- -changes in the number and size of sunspots, the occurrence of solar flares, and the extent of the corona (the outer part of the sun). Although it is not clear how a slight decrease (on the order of 1 percent) in solar activity affects
terrestrial climate, most researchers believe that there is a connection. From around 1450 to 1850, temperatures in the Northern Hemisphere were lower than normal. Glacial advances occurred in the Alps, Alaska, and the Sierra Nevada. Tide gauges in Germany and the Netherlands indicated correspondingly low sea levels. The River Thames in London and the Tagus River in Spain froze over during the winter months. This cold snap has been called the Little lce Age. In the middle of this period, between 1645 and 1715, almost no sunspots were seen. On rare occasions when an astronomer observed one, it was cause for great excitement.
8.Why does the author mention that between 1645 and 1715, almost no sunspots were seen”?
A.To identify the coldest years during the period referred to as the “little lce Age”
B.To support the claim that there is a connection between solar activity and Earth’s climate
C.To explain why the appearance of sunspots might cause excitement among astronomers
D.To suggest that sunspots have a greater influence on climate than do solar flares or the extent of the corona
9.Look at the four squares[ █ ]that indicate where the following sentence can be added to the passage.Where would the sentence best fit?
However, the continents were not always distributed in this way.
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.) Drag your choices to the spaces where they belong. To review the passage, click on view text.Various factors have contributed to Earth’s many cooling and warming cycles over the last billion years.
A.Although it was not a factor in earlier climate shifts, excess carbon dioxide in the atmosphere is responsible for Earth’s most recent warming trend.
B.Over time, variations in the positions of the continents may have caused cooling periods by influencing ocean currents and rain patterns.
C.The increase in the size of sunspots and the more frequent occurrence of solar flares has resulted in shorter and less frequent cold periods over the past bllion years
D.Orbital variations are largely responsible for long-term changes in Earth’s climate, but additional factors probably trigger climate changes more directly.
E.Changes in undersea volcanic activity were an important trigger for glacial epochs during both the Permo-Carboniferous and the late Precambrian
F.While the precise mechanism is not known, changes in solar activity may produce variations in temperature such as the ones that occurred during the Little lce Age.
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