The genesis of Eden.

The Eden Project is to be a huge device for demonstrating the range of biodiversity and the manifold interactions between humanity and the world of plants. The project is to be built in a disused clay pit near St Austell in Cornwall. Location in the southwest of England is a result of local initiative, but the mild climate, lavish rainfall and relatively balanced day length render the peninsula one of the best locations in Western Europe for the experiment.

The landscape of Cornwall is made mysterious and sometimes magical by the local china clay industry, which leaves great white tips and pits as the kaolin is extracted from the rotten granite that underlies much of the rough brown moorland surface. The Bodelva pit is one of these workings and it offers a sheltered south-facing curve surrounded by parkland. Its 14ha area is nearly worked out, and the owners have offered the Eden Trust an option on purchasing the site prepared for building work.

The proposal uses the cliff-like sides of the quarry as support for a series of greenhouses which contain different biomes, areas which reproduce particular climatic conditions to foster cultures of plants from Mediterranean, desert, rainforest and subtropical parts of the globe. The aim is to generate consistent worlds, rather than promiscuously mixing species from different parts of the world - for instance, the flora in the tropical rainforest biome will come from a particular part of the Amazonian jungle, rather than being a mixture of plants from South America, Africa and Indonesia as in most botanical hothouses (other specific territories may be added later). The design of the complex is by Nicholas Grimshaw & Partners and Anthony Hunt Associates, and in some ways the structure resembles that of the Grimshaw/Hunt masterpiece, the continental platform at Waterloo Station (AR September 1993). Trussed steel arches form the basis of the structure. They are connected by pin joints to fixings in the top of the rock walls round the pit and on the old quarry floor. The span and height of the conservatory roofs changes continually with the rise and fall of the rock face with the width ranging from 15 m to 120 m and the pitch changing from 30 degree slopes to flat. Each truss is calculated for its particular position (the analytical and constructional techniques used at Waterloo have shown how this can be done economically). The trusses have a tubular central compression boom which is fattest at the point of maximum bending, a point which differs in each truss according to its curve (the tapers are made by sleeving together standard sections). The compression boom is stiffened by steel rod tie booms which are connected to it by struts. Between each pair of main trusses is a secondary structure in which a simple arched tube is held by struts and ties that connect it to the top and bottom booms of the main arches.

All this is, of course, to support the weatherproof membrane. This is made of lightweight transparent ETFE (ethylene-tetrafluoro-ethylene) foil held in 3 m by 10 m aluminium frames, themselves fixed to the steel structure. Three sheets of foil are held within each frame and are inflated into pneumatic pillows by a low-pressure air system which is continuously monitored by an electronic building management system. The skin is expected to achieve more than 90 per cent transmission of visible and ultraviolet light, but the transparency can be reduced locally by pigmenting the film. The pillows are sensitive to imposed loads and can be pressurised individually by fans at the base of the arches which are powered by solar voltaic cells: the skin is in effect flexed by the sun's energy.

In summer, temperature in the conservatories is held down by encouraging convected ventilation from the base of the curves to their upper connection with the rock walls. For the hottest times, there is a powered ventilation system, and the rock walls are used as a thermal sink, which soaks up heat in the day and emits it at night, balancing diurnal temperatures. In winter, there is artificial heating, balanced by the thermal storage of the rocks and internal lakes.

The whole affair is approached, from the southern lip of the pit, whither visitors arrive by shuttle bus from the car park. They descend to a visitor centre, the oval glazed carapace of which slithers down the quarry side like a huge and elegant prehistoric crustacean. From here, visitors cross a bridge over the pit floor to enter the first of the biomes (Mediterranean) which is the start of a kilometre long walk through the whole complex. The basic route is clear, from biome to biome with restaurants and service spaces at each junction. But, particularly in the rainforest section, there are several internal paths, some well above ground level, so visitors can appreciate the ecologies of the different levels. (The structure rises to 60 m in this biome, and it is the only greenhouse in the world able to contain full-grown tropical trees.) This enfilade-like arrangement of internal circulation can be subverted at many points by leaving the heat of the conservatories to walk through the garden at the bottom of the old quarry which is laid out with species native to Cornwall, and with other temperate species related to the ecologies inside (for instance New Zealand and Tasmanian flora next to the subtropical biome).

Eden is a big, brave and exciting project that will not only offer instruction and entertainment to the public but provide a centre for research into environments that are rapidly being degraded in their natural locations. Using some of the most ingenious creative thinking in Britain today, it relates the nation's past, as one of the scientific cultures most concerned with flora in every way, to an unknown future in which the world of plants will certainly have to be taken much more seriously than it is now. It is proposed as a candidate for major funds from the Millennium Commission which is funded by the National Lottery. If the commissioners decide hot to support it, the millennial celebrations will be shown to have the lack of cultural guts that dogs most other aspects of life in these islands today - and makes backward-looking Britain a laughing stock worldwide. P D