How deep is the ocean?" crooned Bing Crosby in the popular 1930s Irving Berlin ballad - a question not much closer to being answered 70 years later. In fact (comparatively speaking), little is known about the great watery depths between the continents, even though they are increasingly trawled and travelled across. A recent estimate suggests that, as we enter the 21st century, we have investigated less than 10 per cent of the total ocean area and less than 1 per cent of the deep ocean trenches.
School geography lessons are overwhelmingly geared towards land-based topics - towards that 30 per cent of the Earth's surface which humankind has been able to colonise safely. The other 70 per cent has always received scant attention. Yet as the world becomes over-crowded and resource-depleted, it is surely likely that it is the seas and the oceans to which we shall increasingly turn for solutions.
Hence, in 2004 the Young Geographer of the Year competition, sponsored by The TES and Geographical magazine, takes as its theme "The future of the oceans" and invites students to speculate - after arming themselves with the best expert knowledge they can find - about what might happen to the major part of the Earth's surface in their lifetime.
The oceans are the last unconquered frontier of exploration on Earth.
Although there have been past pioneers who have descended to the depths, such as Jacques Cousteau and Auguste Piccard in their bathyscapes, occasional major fact-finding expeditions (the Royal Geographical Society's recent Shoals of Capricorn project), and commercial surveyors making hydrographic charts a-plenty, relatively little is known about the shape, nature and sustainability of these great bodies of water and what lies beneath them.
In recent years, increasing concern has been expressed about the human capacity to damage and pollute the oceans, and sea voyagers report back with alarm the trails of oil slicks, the collections of litter and the ominous build up of phosphates in the water of the great sea lanes. There is particular worry about the fate of coral reefs, which are a magnet attraction for tourists and which are being eroded at a rapid rate through human action in some areas. The coral plays a role akin to the rainforest - it's a home and breeding-ground for thousands of creatures and its destruction has widespread ramifications.
But beyond the main roads of the sea, the oceans seem to have a prodigious capacity to restore themselves and absorb the worst that humanity can throw at them. At least, so it has been so far. But are we approaching the end of the ocean's ability to cope? The salutary story of how Fenland soils were eventually depleted by profligate farming after years of providing apparently inexhaustible nutrients serves as a warning that time may be running out for the "throw it in the sea and don't worry about the consequences" brigade (whose members range from holiday-makers to governments and some transnational corporations).
The front page of a student-oriented geography magazine recently pointed to a paradox in its headline "Not enough water?". An article inside explored the assumption that the world's population might not have enough fresh water to survive in the future. Given the vast capacity of the oceans (1,000 billion billion litres of water is one current estimate), the question of desalinisation of ocean water must surely be a possible solution to this problem. Can such a process be made technologically feasible on a widespread and economic scale? If so, in meeting human needs, what are the knock-on effects on the oceans themselves?
There are, as we dimly know, immense food chains dependent on particular water conditions; the loss of one species in one part of the world may cause catastrophic effects on other species elsewhere. There is already alarm about the over-fishing of particular seas, but then most of the world's fishing boats operate on a primitive hunter-gatherer basis. Can we farm the oceans productively so that a marine economy mirrors the productivity so dearly sought on land?
North Sea gas and oil provided a welcome boost to Britain's economy in the last century, as a kind of bounty which the seas revealed when the message from land-based energy sources was one of doom and gloom. What resources lie untapped beneath the Atlantic, the Pacific and the Indian Ocean can only be guessed at. These may well be the salvation of another generation.
But great technical challenges lie ahead in making them available. If the cost of extraction is greater than the commercial value, then a potential resource will remain untapped.
Although little has yet been attempted, we might also one day turn to the oceans as places of settlement. The idea of living in cities under the sea is still largely fanciful and fictional, but it would not take much for crowded states on the littoral to expand seawards sometime in the 21st century.
The oceans are also susceptible to wider planetary events. Global warming may well release ice-caps into the oceans and so change the pattern and strength of sea currents, as well as alter the configuration of land masses. El Nino ("the child") may become a fully-grown adult and cause either havoc or delight as it changes its velocity and its path. Is there anything humans can do to alter or even predict such far-reaching events?
Beyond all this lie complex questions of territoriality, as the supposed neutrality of some ocean waters is increasingly threatened by the legal eagles of governments, anxious to protect and extend their own interests.
The day might come when nation states seek to eliminate the concept of "the open sea" altogether. The extended territory within the sea-boundaries of the Falkland Islands was as critical a factor in the conflict with Argentina as the dispute about the ownership of the islands themselves.
Will the large oceans be the next location of international conflict, as countries lay claim to newly-discovered resources, or seek to strengthen their defensive shields?
All these issues are central to a geography which encompasses the future.
We hope that entrants to the 2004 Young Geographer of the Year contest will seek to grapple with them. Bodies such as the Pew Oceans Commission, the Centre for Sea Change and the Living Oceans Society in the US, and Southampton Oceanography Centre are in the forefront of study and research and can be sources of information, as well as purveyors of informed opinion.
If teaching in schools is to deal with the key issues of the 21st century, we will need to find more room for discussing the oceans and their future.
Perhaps most clearly and practically "sustainable development", already a theme in many geography syllabuses, can and should be interpreted as wider than just a land-based topic. There is some space for maritime geography in present curricula, but there needs to be more.
For full details of the Young Geographer of the Year competition see next week's Teacher Further informationwww.rgs.orgeducationwww.bbc.co.uknatureprogrammestvblueplane twww.livingoceans.orgwww.enchantedlearning.comsubjectsoceanshttp:mbgnet.lt;NIPgt; mobot.orgsaltoceanswww.mos.orgoceansresourcesindex.htmlRex Walford is a fellow of Wolfson College, Cambridge and a judge of the Young Geographer competition