Animal, mineral, edible?

We are what we eat - and it has a lot to do with rocks. Michael Bateman gets a geologist's-eye view of the dinner table Beef is, to the geologist, a complex mineral cocktail

IT RESEMBLES a surreal scene from a Peter Greenaway film. A spotlight illuminates a group dining in London's Natural History Museum. The backdrop is a weird collection of petrified whales' teeth, Jurassic ammonites and gnarled volcanic rock from the beginning of time, exhibits in the Lasting Impressions Gallery.

As uniformed waiters attend the group of diners , it's easy to imagine a Greenaway camera panning the museum exhibits. Here it picks out a 10ft section of tropical bamboo, twice as thick as drainpipe, representing the hasty urgency of the life-force; these plants can grow a startling metre per day. The camera might move on to an ancient stone stained with dull green Arctic lichen, which grows a mere millimetre every 50 years. (Lichens may be among Nature's slowcoaches, but some have a life expectancy of 10,000 years.)

It's a strange setting for a formal dinner, but these are members of the Geological Society. Film producer Martine Benoit of Geo Films has arranged the event on the theme of the Geology of the Table. The diners include her partner, John Simmons, the museum's Keeper of Mineralogy, Professor Paul Henderson, Dr Brian Taylor of the British Geological Survey, plus wives and friends.

To most of us, food is what we buy in a shop. To the geologist it is the end product of a food chain which has its source in numerous life-giving minerals. Indeed, all life can be traced back to an atom of carbon. "Man is made from rocks, water and time," says John Simmons. "Isn't that amazing?"

He raises a glass of champagne, made from the Chardonnay grape, which feeds on the remains of our most distant ancestor. Champagne grapes grow around Reims, digging their roots 10-15ft into the chalk beds below. "And what is chalk," asks John Simmons, "but the compressed shells of a minuscule creature called a coccolith, one of the earlier forms of life on the planet. It is a cross between algae and shellfish, and measures a fraction of a micro-millimetre."

Professor Henderson flourishes an A4 photograph of a fossilised example. It doesn't seem at all small but that's because it has been magnified 16,000 times. The coccolith, it has to be said, is a thing of staggering beauty, a decorative structure blooming with fluted mushroom shapes. We raise our glasses to toast the coccolith, our common forefather, and sip the champagne from vines which grew on their remains.

Dinner is soon under way. The first course is moules marinieres, to symbolise mankind's long-standing affinity with shellfish. In Japan they still eat a variety known as lingula, a perfectly symmetrical ovoid that buries itself in the estuary mud. At 600million years of age, it is our most ancient food source.

Our main course is beef. Dr Taylor stabs a piece on to his fork. To nutritionists it is protein and fat; to the geologist it is also a mineral cocktail of iron, calcium, sodium, potassium, magnesium, manganese, copper, sulphur and chlorine. Humans, animals and insects take up minerals from the soil via leaves, grasses, plants and roots, he explains. Only 40 years ago, says John Simmons, this simple fact led to one of the most significant applications of geological science.

Step forward the Isaac Newton of modern geochemistry, Professor John Webb. Searching for mineral deposits in Africa in the 1950s, he discovered that minerals below the soil could be identified by analysing trace elements in grasses, plants and the leavesof trees. Using the Webb method, the mineral deposits of the world have since been mapped.

Nice for the mining companies, but is there an application to food? Certainly, says John Simmons. In Somerset, cattle were found to be suffering from a condition associated with lack of copper in their diet: poor appetite, low fertility, diarrhoea. Yet there was apparently copper in the soil. Turning up Webb's map of Somerset, geologists discovered that also present in the soil was a mineral called molybdenum. In the animal's gut it combines with copper, preventing it from being absorbed. With the helpof copper supplements the animals quickly recovered.

Pass the salt, please. Alas, salt is to the geologist what a red rag is to a bull. Salt is the cue for the awful revelation that a billion people in the world suffer from a preventable illness, cretinism, an incurable state which in extreme cases leaves people malformed, dumb, blind and unable to control their motor functions.

It is entirely due to a deficiency of iodine (usually present in common salt) in the diet. "If the World Health Organisation hadn't other problems on its hands, like the world's continuing cycle of famine, they might try to put it right," says John Simmons.

He gives a modern illustration. Cretinism was suddenly noted in the young children of natives in Papua New Guinea, where it had not occurred before. The reason was that for centuries salt had been gathered twice a year from rock pools and indeed was regarded as so precious it was used as currency. So when international companies moved in to exploit local resources, they paid for land with bags of salt.

"Soon pregnant mothers began to develop goitre due to a deficiency of iodine, which the imported salt did not contain. So their children were born cretins. Now they have a law that all salt must contain iodine."

It was a relief to turn away from talking about minerals and scrutinise the menu, prepared by the caterers. A temporary relief. The geologists hurried to explain that it had been printed on tree pulp and stiffened with clay. It was dyed with titanium dioxide, the same mineral responsible for the white of our dinner plates.

Other minerals contributed to the coloured patterning; had we been dining in the 1930s, they said, yellow patterning would have been provided by uranium salts. However, uranium production was soon to be diverted to make the first atom bombs. This lesson could go on all night, but enough is enough. The wine is nice, anyway.

Step forward Professor Henderson, with two bottles of Beaujolais. Both are made from the Gamay grape, and produced no more than three kilometres apart, he says. How is it possible they should taste so different? We sip away. The Moulin-a-Vent is the tougher of the two - metallic, slightly bitter, almost like a young claret in its hardness. The Morgon, we agree, is by contrast flowery, fruity and open.

Dr Taylor explains, as you may already have guessed, that the answer lies in the soil - or at least in the sub-soil. "The Moulin-a-Vent is grown on a substrate of granite. Morgon is grown on schist."

Schist? Metamorphosed rock, explains John Simmons - rock that has been changed, compressed, heated and folded to such an extent that a completely new texture emerges and new minerals develop.

And that's why Morgon tastes as it does? Yup. And four other fruity Beaujolais appellations grow on the schist - Brouilly, Cote-de-Brouilly, Julienas and St-Amour. On the granite grows the other Beaujolais, Moulin-a-Vent, together with Fleurie, Chiroubles and Chenas. You should be able to taste the difference between the two groups.

Our tasting seems to confirm the geologists' theory. It also provides a new word for wine buffs and wine bluffers - "schistosity". But wait a minute. These wines were made in different years: the Moulin-a-Vent in 1992, the Morgon in 1991. Surely each year's weather conditions affect the flavour of the grapes differently? Martine Benoit claps her hands with obvious glee. "Oh, good," she says. "We'll have to do the whole thing all over again." (Fade out completely.) !