Buried more than three kilometres beneath the ice sheet of Antarctica is a large liquid freshwater lake called Lake Vostok. It has remained buried under ice for over a million years.
Scientists are very eager to examine Lake Vostok, particularly to see if it harbours life. Any discoveries will change the odds about the possibility of finding life forms off this planet.
The story of Lake Vostok is told by Erica Goldman in the January/February 2001 edition of The Sciences.
Lake Vostok lies beneath a Russian Antarctic science facility, Vostok Station, in the remotest, harshest part of Antarctica. In the mid-1960s Andrei Kapitsa, a Moscow State University geographer, made seismograph measurements which suggested a large body of liquid water lay beneath the ice at Vostok Station.
These data were re-examined by an international team in 1996 and, when combined with other data, clearly confirmed Kapitsa's proposal. The international team further suggested that the lake might harbour life.
Lake Vostok is not the only intriguing lake associated with Russian science - Lake Baikal in Siberia is another. This lake is over 1.6km deep, making it the world's deepest, and it contains one fifth of the world's fresh water.
Lake Baikal hosts an enormous diversity of life. It has 2,500 animal species and sub-species, 82 per cent of which are seen nowhere else on Earth. It supports the only species of seal that lives exclusively in fresh water.
Lake Tanganyika in Africa is about the same age and size as Lake Baikal, but it contains only half the number of species and subspecies. Scientists are eagerly studying Lake Baikal in an attempt to discover what drives the evolution of such abundance.
It is thought that the same geological forces account for the formation of Lakes Baikal and Vostok. The Earth's outer crust is cracked, dividing it into several great tectonic plates that slowly move about on the partly-molten underlying layer of the Earth.
Lake Baikal is a rift lake, that is, it was formed where two tectonic plates are moving apart from each other, making the lake long, narrow and deep, similar to features found at Lake Vostok.
Lake Baikal has hydrothermal vents on its lake bed through which warm chemical-rich water enters the lake. It is the only freshwater lake in the world known to have such vents.
Where these vents occur in the ocean floor they support a variety of strange animals capable of living in the absence of sunlight. Lake Baikal is ancient, formed 15 to 30 million years ago, and it is thought that Lake Vostok is of the same vintage.
How does Lake Vostok remain liquid despite being buried under so much ice? Yes, you've guessed it - probably because it receives heat from the earth beneath.
Also, the thick overlying ice sheet insulates the lake from Antarctica's extremes.
There are several scientific bases dotted around Antarctica making detailed studies of the area. One of the studies routinely carried out is to drill and extract long narrow cylinders of ice (ice cores) from the ice sheet. These cylinders record chronologically, from top to bottom, a record of the past 420,000 years of snowfall.
The snows that fell carried with them the various dusts and gases that were in the atmosphere in times past. By analysing the ice cores scientists can draw a time line of the Earth's past climate and, perhaps, predict future climatic conditions.
In 1998 an extremely long ice core, more than 3km long, was taken in sections at Vostok Station. Most of the core was similar to other ice cores from Antarctica. The ice crystals were small and packed tight.
But, around the 3km deep mark, the appearance of the core changed markedly, becoming more transparent and containing larger crystals. A possible explanation for the change is that the bottom section of the core is not frozen snow fall, it is refrozen water from Lake Vostok.
The really interesting thing is that microscopic examination of the refrozen water revealed several types of bacteria. This strongly suggests that the lake may harbour bacteria capable of living under extreme conditions of cold and pressure and completely cut off from air and sunlight.
If this turns out to be the case, it enhances the exciting possibility that similar life may exist in the ice-covered oceans that have been discovered on Europa and Calisto, two moons of Jupiter.
Investigators are now excitedly preparing to send a probe down into the liquid waters of Lake Vostok. The 3km-long ice core ended 120 metres above the liquid water. Great care must now be taken to ensure that probing the lake does not introduce any contamination into this unique environment.
A mechanism must also be devised to get samples from the lake up to the surface for detailed laboratory examination, again in a manner that does not allow contamination to enter Lake Vostok.
A further consideration also arises. If Lake Vostok harbours bacterial life, this life has been evolving for the past million years in a unique environment, sealed off from the surface of the Earth.
The human immune system would never have encountered such a bacterium, and if it were toxic to humans we would have no defences against it. The greatest care must therefore be taken to ensure that any such bacterium does not escape into the environment when it is raised from its deep, cold, dark world.
It will take several years to design the scientific study of Lake Vostok. Biologists around the world await the results with bated breath.
(William Reville is a Senior Lecturer in Biochemistry and Director of Microscopy at UCC.)