The third dimension

摘要

Drifting through the world's oceans at all levels - from the water surface down to the seabed - and in an amazing array of colours, shapes and sizes, it's plankton that really makes the world go round. Gazing seaward from a deckchair at Bognor Regisor the silver sands of a Caribbean island, you could be for- given for thinking that the Flat Earth Society got it right. All you can see is a dead flat horizon on all sides. Water - as anybody who endured last winter's floods will testify - finds its own level. A river breaks its banks and every connected square millimetre below that level floods equally. There are no exceptions. But, as we all know, the world is not flat. It is round, and gravity stops us - and water - falling off. The layer of waterstuck onto the planet in this way is so thin when compared to the mass of the Earth that if it were a billiard ball it would only just feel damp; and compared to the film of moisture, the land would only register as a polished surface. Yet the 'dampness' of the oceans represents a biome 6,000 times the size of the biome presented by terrestrial habitats, even though it is only three times the area. That extra multiple of 2,000 results from the fact that only the oceans provide living organisms with a truly three-dimensional habitat to explore and exploit. Terrestrial organisms have only a two-dimensional- or, in the case of birds and flying insects, a very shallow three-dimensional- space to rummage around in. Add to this the fact that the water has been around in a colonisable state for about twice as long as the land, and it should come as no surprise that the oceans hold a biomass and variety of life forms that dwarfs the equivalent on land by several orders of magnitude.