Evolution in a few simple steps

SCIENCE Kew's new 'time machine' will take you back 4,000 million years. Gail Vines ventures in

THERE was a blackbird singing in the Tem-perate House the day I visited Kew - a cheerful complement to the lush vegetation. Yet had it flown a few metres further, to the glasshouse next door, it might have felt rather less at home. For the landscapes in Kew's new Evolution House flourished long before birds evolved. A blackbird in their midst would be as appropriate as a mobile phone in the Stone Age.

The Royal Botanic Gardens at Kew has built a time machine, designed to transport visitors back 4,000 million years. Squeezed into a small aluminium- framed glasshouse, it is not all that much bigger than the Tardis. But once you're inside, it's surprisingly spacious. The carefully planned interior design blocks distant views, and encourages you to look up or down. Following a winding path you walk through what is almost a series of rooms.

The entrance is dominated by a pool of bubbling primeval mud, representing the environment in which primitive life first evolved, some 4,000 million years ago. John Lonsdale - head of Kew's technical section - had to fight for the pool. "Everyone said children would wade in," he says. The solution was an invisible safeguard: a grid fixed a few inches below the surface.

The bubbles glug hypnotically to the surface at odd intervals. The trick is a lidded box at the bottom, connected to an air hose: when the air pressure is high enough, the lid pops open and a bubble rushes out. To complete the primeval landscape, there's a miniature volcano equipped with belching steam and glowing "lava". You can just detect the sound of distant rumblings and a whiff of sulphur in the air.

Round the corner, 3,500 million years ago, life, in the form of the cyanobacteria, or blue-green algae, appears on the scene. These unprepossessing organisms, faithfully recreated by scientific model-makers in Missouri, sparked off a global climate change that set the scene for the evolution of everything else. Around long before anything had evolved to eat them, cyanobacteria rapidly spread across the globe. They trapped energy from sunlight - the process of photosynthesis - and gave off free oxygen. After some 2,000 million years, they had inadvertently created an atmosphere in which other organisms could breathe.

Cyanobacteria can also take credit for the ozone layer, the protective shield against ultraviolet radiation which further paved the way for the colonisation of land. You can read the rising oxygen levels in the rocks: iron-bearing rocks of this age began to look red, as the iron was oxidised by the atmosphere. And so the evolution house's "rocks" - glass-reinforced concrete moulded from real rocks - turn from the grey basalts of primeval mud days to red sandstones.

Round a sharp bend, you enter the Silurian period, about 400 million years ago, and meet another unsung hero of plant evolution. The fish that first crawled on to land is a familiar image, but who ever hears about the plants that conquered the earth so much earlier? Look down at your feet and you'll see "a giant leap for plantkind", as Lonsdale calls it: the first upright plant with true stems, Cooksonia. Long extinct, Kew's Cooksonia are made of plastic, and look like tiny tuning forks with knobs (spores) on the ends. These modest plants invented specialised thick-walled cells that transported water and nutrients and strengthened the stems, so the plants could stand upright and waft their spores about; thus colonising yet more virgin territory.

A bit further on in time and space you come to the first living plants in the evolution house, modern liverworts and mosses standing in for their ancient ancestors. But living plants in the time trail create unique headaches for the horticulturists of Kew. As enduring species, the liverworts and mosses can grow "forward" in the exhibition, but they must not be allowed to grow "backwards" and so muddle the evolutionary sequence. "It's quite a challenge gardening in four dimensions," Lonsdale contends.

Under the rock bridge, you come to the Devonian period, when the first seed plants, the seed ferns, make their initial appearance. From there, it's a few steps to the centrepiece of the house: the coal swamps of the Carboniferous period, some 300 million years ago. Living tree ferns, horsetails and ferns grace a reconstruction of an ancient swamp, dominated by giant extinct club mosses, or lycopsids - the models reach more than 7.5 metres into the roofspace. On one stem sits a model of the giant dragonfly Meganeura, with a wingspan of half a metre. Across the swamp lurks an extinct woodlouse the size of a corgi, which once dined within the decaying stems of the tree-like lycopsids.

But what would the Carboniferous period have sounded like? Evolution experts advised the designers to avoid buzzing sounds, as flies and bees had not yet evolved. So they electronically manipulated a variety of whirring and clattering insect noises that dragonflies and cockroaches might have made, and added the eerie call of a primitive amphibian, "produced from the throat of palaeontologist Eric Gyllenhaal". The sound comes from hidden speakers, which are activated as visitors cross a light beam.

The Jurassic period is signalled by a dinosaur's footprints crossing the path to the sound of crunching foliage. Further on, a grove of living cycads marks the Cretaceous period, 100 million years ago. The landscape is dominated by a sandstone cliff, with waterfalls and pools, as the exhibition culminates with the blossoming of the flowering plants.

The evolution house is Kew's first foray into "landscape immersion", an exhibition style pioneered by Disneyland and theme parks to "bring ancient times to life". It's a deliberate move away from the traditional idea of a botanical garden, bursting with as many specimens from as many parts of the world as possible.

But Kew has worked hard to guarantee authenticity in the midst of artifice. The simulated rocks, animals and plants have been painstakingly planned for both scientific accuracy and visual appeal, and living specimens have been introduced only if they are bone fide relations of ancient plants. Vigilant weeding keeps rampant mosses from growing illicitly "backwards" in time - although I did notice one or two ants visiting the Cooksonia.

Yet what, I wonder, do people really take away with them? Marketing surveys carried out to date suggest that visitors enjoy the bubbling mud, the smells, the insects, the giant models of extinct trees. But they really informed?

Lonsdale acknowledges that the exhibition has teething troubles. "We are trying to discover how best to put information over without destroying the believability of the landscape," he says. After toying with the idea of videoscreens in rocks, the team hit on using "pools of sound" - recorded messages triggered by passing visitors and focused so as to be audible only in the right spot. Unfortunately, in a packed house there is considerable aural overspill, making the "time statements" difficult to hear.

The team has yet to work out how best to tell visitors "when" they are, and what they're seeing. Nonetheless, Lonsdale is committed to "landscape immersion", and hopes to recreate the Australian outback in a corner of Kew. I wonder what the blackbird will make of that. !