雅思阅读第084套P1-Lake Vostok

Lake Vostok

A

Beneath the white blanket of Antarctica lies half a continent of virtually uncharted territory – an area so completely hidden that scientists have little clue what riches await discovery. Recently, Russian and British glaciologists identified an immense lake – one of Earth’s largest and deepest – buried beneath 4,000 meters of ice immediately below Russia’s Vostok Station.

B

As details have emerged, a growing number of scientists are showing interest, with dozens of investigators keen to explore the feature, known as Lake Vostok. A thick layer of sediment at the bottom of the lake could hold novel dues to the planet’s climate going back lens of millions of years. By looking at the ratio of different oxygen isotopes, scientists should be able to trace how Earth’s temperature changed over the millennia. NASA has expressed interest in Lake Vostok because of its similarity to Europa. This moon of Jupiter appears to have a water ocean covered by a thick ice sheet, measuring perhaps tens of kilometers in depth. If hydrothermal vents exist beneath the ice, chemical reactions on Europa could have created the molecular building blocks for life, if not life itself. Vostok would be an ideal testing ground for technology that would eventually fly to Europa or places even more distant, say many scientists. Though cheap compared with a Europan mission, any expedition to Vostok would represent a significant investment.

C

Vostok Station holds the uncomfortable distinction of having recorded the coldest temperature on Earth. Thermometers there measured in July 1983, and the average temperature hovers around -55ºC. It’s the thick ice, strangely, that enables a lake to survive in such a frozen environment. The 4 kilometers of ice acts effectively as an insulating blanket protecting the bedrock underneath the ice from the cold temperatures above. Geothermal heat coming from the planet’s interior keeps the lake from freezing and warms the lowest layers of ice. The tremendous weight of the ice sheet also plays a role in maintaining the lake. Beneath 4 kilometers of glacier, the pressure is intense enough to melt ice at a temperature of -4°C. These factors have helped lakes develop across much of the thickly blanketed East Antarctica. More ore than 70 hidden lakes have been detected in the small portion of the continent to date. Lake Vostok is the largest of these, stretching 280km from south to north and some 60 km from east to west. At Vostok station, which sits at the southern end of the lake, the water depth appears to be 500m according to seismic experiments carried out by Russian researchers.

D

The first clues to Lake Vostok’s existence came in the 1970s, when British, U.S., and Danish researchers collected radar observations by flying over this region. The radar penetrates the ice and bounces off whatever sits below. When researchers found a surface as flat as a mirror, they surmised that a lake must exist underneath the ice. An airborne survey of the lake is being undertaken, the first step toward eventually drilling into the water. Along with the potential rewards come a host of challenges. Researchers must find a way to penetrate the icy covering without introducing any microorganisms or pollutants into the sealed-off water.

E

What about life in the depths? If tiny microbes do populate the lake, they may be some of the hungriest organisms ever discovered. Lake Vostok has the potential to be one of the most energy-limited, or oligotrophic, environments on the planet. For the lake’s residents, the only nutrients would come from below. Russian investigators have speculated that the lake floor may have hot springs spewing out hydrothermal fluids stocked with reduced metals and other sorts of chemical nutrients. Scant geological evidence available for this region, however, indicates that the crust is old and dead. Without a stream of nutrients seeping up from the deep Earth, the only potential source of energy lies above the lake. The ice sheet above the water is creeping from west to east at a rate of roughly four meters per year. The lowermost layers of ice melt when they come in contact with the lake, liberating trapped gases and bits of crushed-up rock. If the glacier recently passed over rock before reaching the lake, it could be supplying organic compounds useful to microorganisms. It also could be seeding the lake with a continuous source of new residents. Bacteria, yeasts, fungi, algae and even pollen grains have been found in the Vostok ice core samples taken down to depths of 2,750m – three quarters of the way to the bottom. At least some of these organisms are alive and capable of growing, according to recent reports. The results of this analysis may indirectly indicate whether anything survives in the lightless body of water.

SECTION 1: QUESTIONS 1-13

Questions 1-4

The passage has 5 sections A-E.

Choose the most suitable heading for sections B-E from the list of headings below.

Write the appropriate numbers (i-viii).

There are more headings than sections so you will not use all of them.

Example:

Section A v

1 __________ Section B

2 __________ Section C

3 __________ Section D

4 __________ Section E

Questions 5-6

Choose the correct letter A-D.

5Which is NOT given as a reason for interest in exploring Lake Vostok?

Ato test technology for space exploration

Bto develop anti-pollution devices

Cto investigate the history of Earth’s climate

Dto look for living organisms

6Lake Vostok does not freeze because …

Aa thick ice cover provides insulation.

Bit is waned by heat from the earth’s surface.

Clow pressure prevents freezing.

Dan underwater volcano erupted recently.

Questions 7-13

Do the following statements reflect the claims of the author?

Write:

7 _________________ Only one lake has been found beneath Antarctica.

8 _________________ Lake Vostok was detected by radar.

9 _________________ Exploration of Lake Vostok is coordinated by Russia.

10 _________________ Nutrients to support life have been found in the Antarctic ice.

11 _________________ The ice above the lake is moving to the east.

12 _________________ Scientists have drilled through the ice into the water of Lake Vostok.

13 _________________ The water in the lake is approximately 500 in deep at the southern end.