Dry Storeroom No. 1 (38 page)

Alex Ball and Terry Williams are in charge of the Kingdom of the Machines that now occupies the basement area under the Earth Science galleries, and they will take you from room to room with proprietorial pride. The first thing you notice is how clean everything is compared with the average cluttered Museum office. Record books are neatly filed away above wiped-down benches—the word “shipshape” comes to mind. The Natural History Museum is rather well off in the latest technology, although, as Alex remarks, you have to run hard just to stay up with the leaders. Many university departments have to make do with one analytical machine that has to be constantly reprogrammed, but the Museum can find a machine to suit the job in hand, which means going into one dedicated room or another. Before the basement was commissioned, the machines were dotted about the Museum in obscure places. The first scanning electron microscope (SEM) was up and running in the Museum (1965) even before I joined the staff, thanks to the efforts of Ron Hedley, who later became the Director. He recognized its importance as a tool to see fine structures more clearly than ever before, by using electron beams that could discriminate detail much more finely than the traditional light source. It is easy to forget the astonishment of being able to see for the first time the eye of a fly, or those “hairs on legs,” with such precision.

Electron microscopy is located in the Mineralogy Department. Images provide unrivalled details, even of fossils. Here (
above
) A photograph of the Cenozoic bryozoan (
Exochella jellyae
Brown, 1952) can be compared with the drawing of the holotype of Brown made in 1952 (
bottom
).

This tool transformed the study of some animal and plant groups. Paul Taylor, the doyen of the bryozoans, is always stressing the beauty of his tiny, water-dwelling and mat-forming colonial animals—and he is right. Before the SEM these animals were usually illustrated by drawings, which varied greatly in quality. Now the exquisite and delicate patterns made by the colonies and the ornament of the little boxes in which each individual of the colony lived are both scientifically accurate and a delight to the eye thanks to the electron microscope. The scanning microscope was soon complemented by the transmission electron microscope, an instrument that has transformed our understanding of the organelles inside living cells and the way those cells collaborate to make tissues. I used the scanning electron microscope quite early in my Museum career. I always felt like a
real
scientist when I sauntered off to the machine. I soon had images of trilobite larvae a millimetre long blown up to the size of a small lobster, displayed on the green plasma screen attached to the microscope. The process of photography was slow because specimens had to be coated in a fine layer of gold to allow the electrons to “take” later machines allowed photography of uncoated specimens, and these are still in use today.

So machine was added to machine, one by one, each with its own acronym, each doing a somewhat different job. For example, many mineralogists were not interested in getting good pictures so much as in analysing elemental composition. Much of the serious research money in the Museum came to be spent on this hardware. The latest version of the electron microprobe cost half a million pounds, but it saves much staff time because it is automated to assay for four elements simultaneously, and gradually works through an elemental “shopping list.” Mineral samples are analysed from polished surfaces of rock slices, or they are sometimes powdered, or put into solution, depending on the technique involved. Machines have to be continually updated as new levels of accuracy of measurement are achieved—so, for example, they can now routinely focus on minute areas just a thousandth of a millimetre across if required. The mind soon reels when confronted by the variety of “kit” in the Kingdom of the Machines, but I was happy to see my old machine still sitting in one of the rooms.
^*20

Some mineralogical investigation is closer to industry than most of the research that goes on in the Natural History Museum. There is money to be made from knowing about how ores or gemstones form in nature. Many valuable metal ores are associated with special rocks known as volcanogenic massive sulphide (VMS) deposits—and, as with SNC meteorites, it might be better to stick with the acronym for reasons of brevity. These are interesting and unusual rocks because most of them originated in ocean basins where cold seawater meets hot fluids from deep within the Earth—yielding sulphide deposits rich in zinc and copper. The metals are dissolved in water as hot as 380 degrees centigrade, and when the metalliferous liquor hits cool sea temperatures the solubility of the valuable ions falls dramatically. The resulting massive metal sulphides can be thick enough to support large quarries. The sites where these strange deposits form today typically lie along the mid-ocean ridges, which is where the lithospheric plates of which the world is made are slowly, slowly moving apart. Heat rises from the interior of the Earth along the ridges, bringing treasure—not just zinc and copper, but silver and gold as well. Sulphurous fluids belch out of vents known as “black smokers” which track the ridges on the ocean floor—and build up dark chimneys of iron pyrites out of sight of the sunlit world above. In the same hidden world thrives a whole ecosystem of bizarre animals, whose economy is based upon the sulphurous exhalations of the smokers rather than upon sunlight. There are shrimps that cultivate sulphur bacteria, or scrape them from the walls of the chimneys. There are vestimentiferan worms that house bacteria in their guts and form thickets of tubes. There are giant clams. It is an extraordinary world, and one that can be visited only in special diving craft like
Alvin,
the U.S. Navy’s deep submergence “submarine” that can withstand the enormous pressures at depth. As far as mining is concerned, it might as well be on the Moon. Many of the “fossil” VMS deposits are associated with former volcanic island arcs, like those around the Pacific Rim today. They are preserved only in accessible locations on the continents because of the inexorable movement of the tectonic plates around the Earth. Pieces of ancient ocean floor finish up incorporated into the continents, and then they are available to miners. Geologists recognize an appropriate tectonic setting, typically where ancient sea floors have been subducted away, and this makes for excellent prospecting.

VMS deposits are important sources of industrial and precious metals. Gold may be the legendary lure for the adventurer, but more commonplace metals like copper may prove to be more relevant to the future of the world. It is a curious thought that the electrical wiring in our homes might have started out on an ocean floor millions of years ago. Richard Herrington is the Museum mineralogist and metallurgist with a special interest in VMS formation. He is full of enthusiasm for heavy dark rocks made mostly of massive iron pyrites—iron sulphide, otherwise known as “fool’s gold”—not one of nature’s most elegant productions to my eye. But his work with Crispin Little of Leeds University and Russian colleagues has cast a brilliant light on ancient oceans, showing that the community of life around “black smokers” has been established on Earth for hundreds of millions of years. These scientists have been working in the copper/zinc mining districts in the Urals, especially around that city whose name leaves little to the imagination, Magnitogorsk. Its famous ice hockey team is the best in Russia and leaves even less to the imagination—they are called Metallurg Magnitogorsk. A glance at a map of the world will show how the Ural mountain chain snakes across the centre of Russia from Novaya Zemlya in the north, by way of some of the new republics, all the way down to Kazakhstan in the south. It is a huge wrinkle on the surface of the globe. This shape alone would suggest to a modern geologist that the Urals represents the aftermath of a vanished ocean—for linear mountain chains like the present Himalaya are thrown up in slow convulsions of the Earth’s crust when continents collide. Just the place for VMSs. The eastern and western halves of Russia came together several hundred million years ago at the end of the Palaeozoic Era. Prior to that they lay on separate plates, and an ocean with offshore islands lay between them—one that was consumed by a subduction zone on its western side. This eventual welding of the two continents together was a long-drawn-out process, and several island arcs found themselves plastered on to the nascent Uralic chain many millions of years before the continents themselves collided—they were the advance skirmishes before the main onslaught.

The earliest vent fauna yet known to science has been recovered from one of these precocious slabs of ancient ocean floor near Yaman Kasy. It is Silurian in age, about 430 million years old. The fossil tubes of vestimentiferan worms are about the dimensions of long macaroni—but transformed into a heavy, blackish metallic-looking mass by the iron pyrites engulfing them. To a seasoned palaeontologist Yaman Kasy provides the most improbable location ever for finding evidence of past life. Normally, volcanic rocks are completely devoid of any organic remains, except in very rare cases where animals have been completely overwhelmed by an ash fall, and the idea of finding fossils in solid lumps of iron pyrites would have most of us slapping our thighs and guffawing. But then, vent faunas are a unique kind of biology, and the rulebook has to be thrown away. Little and Herrington have also found large masses of fossil vent fauna in VMSs of Devonian age in the large copper workings near Magnitogorsk; these are about fifty million years younger than the Silurian occurrence. This fauna includes a large clam and a snail as well as the ranks of tubes belonging to the specialized worms. It is a disappointment to me that no trilobites have been discovered yet in any locality—I have fantasies about them occupying the specialized bacterium-grazing niche that the crustaceans occupy today.

It is an extraordinary tribute to the opportunism of living organisms that even this strangest of habitats should have been colonized so early. There remain some controversial aspects to the interpretation of the fauna: some workers have claimed that the animals were not living as deep as they are today. And Richard Herrington and his colleagues are still putting together the story of the appearance of the Urals, which certainly involves several separate phases of island arcs being accreted to the edge of the ancient continents (arc “docking”), and may also involve major fault movements that slid chunks of ground lengthways along the mountain chain. Differences in metallic composition from one ore body to another can be explained by different origins within the vanished ocean. Richard is working on a complex story of alteration products of VMS by the actions of hot fluids that modify the chemical composition and mineralogy of ores after they are formed. It is a convoluted story, but at the end awaits a better understanding of how our Earth is put together, as well as new sources of wealth. Minerals are the end product of natural cookery in the cauldron of the Earth—and the recipe can be reshuffled several times. Who knows if some tiny crystals may yet prove to be a new species, having waited two hundred million years to receive the blessing of a name?

There are even odder rocks under study in the Mineralogy Department. Carbonate rocks like limestones and dolomites are abundant sedimentary rocks. They form the Cretaceous white cliffs of Dover in England, and the Permian Capitan reefs of the Carlsbad Caverns National Park in the United States. Limestones are just about everywhere, not least as building stones—they flavour much of France, and impart that soft, golden glow to Bath. Many of these rocks were originally formed from chemical precipitation of carbonates from seawater, often associated with bacterial activity, or from the fossils of animals with shells made of calcite or aragonite (these are common forms of calcium carbonate). They are where a palaeontologist likes to go to work; they belong to the world of sea, life and sunlight. Imagine, then, an eruption of carbonates from a volcano. Yet this is exactly what happens when Oldoinyo Lengai, an active volcano south of Lake Natron in the eastern Rift Valley of Africa, bursts into life. The geologist Arthur Holmes described the 1917 event thus: “The volcano suddenly burst into an eruption which lasted several months and shrouded the country for miles with soda-permeated ash. With the first rains the water holes became fouled with bitter salts and many herds of cattle died through drinking from the contaminated pools. Lava that flowed down the slopes of the volcano cracked into irregular blocks looking like grey cement.” It is a weird, bleak place, where all the usual rules of rock behaviour are suspended. These volcanic rocks are known as carbonatites, and they have been studied at the Natural History Museum by several generations of scientists. Some of the earliest samples were collected by the Overseas Geological Survey early in the twentieth century and sent back to England, where Campbell Smith, who eventually became Keeper of Mineralogy, recognized that they were erupted as lavas rather than being limestones caught up in an eruption. Then an incorrigibly amiable scientist, Alan Woolley, subsequently made carbonatites his life’s work, and continues to work on them in retirement, while Frances Wall carries forward their study into the next generation.