PSAT Writing and Language Practice Question 308

Question: 308

Antarctica
To get some idea of what Antarctica is like, think of a place as remote as the far side of the 45 Moon as strange as Saturn, and as inhospitable as Mars. A mere 2.4 percent of 46 its 5.4 million square-mile landmass (50 percent larger than the United States) is ice-free, and that condition lasts for only a few months a year. Scientists estimate that 70 percent of the world's fresh water is locked away in Antarctica's 47 ice cap, if this ice were ever to melt, sea levels might rise 200 feet, inundating coastal lands together with their major cities. In Antarctica, winds can blow at better than 200 mph, and temperatures can plummet as low as ?128.6 degrees (Fahrenheit).48 There's 49 neither a town or a single tree, bush, or blade of grass on the entire continent.
Nevertheless, Antarctica is vital to life on Earth. The continent's vast ice fields reflect sunlight back into space, preventing the planet from overheating. The cold water that the icebergs generate flows north and mixes with equatorial warm water, producing currents and clouds that 50 create ultimate, complex weather patterns. Antarctic seas teem with 51 life—from microscopic phytoplankton and tiny krill at the bottom of the food chain to killer whales and leopard seals at the top giving these waters a vital status among the Earth's ecosystems.52 Unique species of birds and mammals make their homes in the frigid waters of the Southern Ocean that lap the continent's edge, some found nowhere else on the planet.
The relative inaccessibility and near pristine state of Antarctica 53 makes it an invaluable place for scientific research today. Clues to ancient climates lie buried deep in layers of Antarctic ice—clues such as trapped bubbles of atmospheric gases, which can help scientists draw a better picture of what Antarctica was like in the past. Until recently, most scientists thought that Antarctica has been covered by ice for 40 million to 52 million years and that the present ice cap is about 15 million years old. However, the discovery of remnants of a beech forest near the head of the Beardmore glacier, approximately 250 miles from the South Pole,54 provides evidence that Antarctica may have been both ice-free and much more temperate 2.5 million to 5 million years ago than it is now. Similar fossil finds made elsewhere suggest that western Antarctica was perhaps completely ice-free as recently as 100,000 years 55 ago and scientists, as a result, are conducting new research to enhance their understanding of Antarctica's climate changes.

Show Answer