Reading: Matching Information to Paragraphs: Question 1

A More than four hundred bodies of liquid water have now been mapped beneath the Antarctic ice sheet, hidden under as much as four kilometres of solid ice. Because the overlying ice has sealed some of these subglacial lakes off from the outside world for periods estimated at several hundred thousand years, researchers regard them as among the most isolated environments on the planet.

B Despite lying beneath a permanently frozen surface, the water in these lakes does not freeze solid. The immense weight of the overlying ice raises the pressure at the base of the sheet enough to lower the freezing point of water, while a slow but steady trickle of heat rising from the rock below is generally sufficient to keep the lake liquid even though surface conditions nearby remain far below zero.

C Reaching a lake without contaminating it is an exacting engineering problem. Teams typically melt a narrow borehole using a heated water jet, filtering and sterilising every litre of drilling fluid before it enters the ice so that microorganisms carried down from the surface cannot later be mistaken for anything native to the lake once a sample is finally retrieved.

D With no sunlight able to penetrate the ice above, any organisms living in these waters cannot rely on photosynthesis. Instead, some of the microbes recovered from meltwater linked to these lakes appear to draw their energy from chemical reactions involving minerals dissolved out of the surrounding bedrock, a process known as chemosynthesis that also sustains certain communities on the deep ocean floor.

E For planetary scientists, the discovery that microbial life can persist in permanent darkness, under crushing pressure, sealed away from the open air for millennia, has become a natural reference point when discussing the icy moons Europa and Enceladus, both of which are thought to hide oceans of liquid water beneath a frozen outer shell.

F Not every scientist agrees on how freely these lakes should be studied. Some argue that each new borehole risks introducing surface contamination into an ecosystem that has never before been disturbed, and have pushed for a small number of reference lakes to be left completely untouched, while others maintain that the scientific value of sampling outweighs this risk provided sterile protocols are followed.

Which paragraph contains the following information?

Write the correct letter, A–F, for each statement.

NB You may use any letter more than once.

1. A suggestion that conditions in these lakes could resemble those found on icy moons elsewhere in the solar system.
2. The total number of subglacial lakes that have so far been identified beneath the ice sheet.
3. A description of the precautions taken to avoid contaminating a lake while drilling down to reach it.
4. An explanation of how organisms in these lakes are able to obtain energy without sunlight.
5. A reference to disagreement among scientists about how freely a pristine lake should be sampled.
6. An explanation of why the water in these lakes has not frozen solid despite the extreme cold nearby.