The field laboratory fabricated by staff on a shoestring budget that toured Africa collecting insects in the 1970s: systematic labour that is never finished
Modern methods of characterizing species employ molecular sequencing to identify a characteristic part of the DNA of each species as a “bar code” this speeds up the process of characterization and recognition. But this process leaves out everything else. Every species has its own tale, a story about how it earns its living, meets its mate or warns off its enemies: the interesting stuff. You don’t understand London just by reading the names in the telephone directory.
As we have seen, beetles will eat anything—even slime moulds. In damp woodland you may notice pink or brown blister-like masses of spores sitting on rotten logs: these are the reproductive structures of some of the larger slime moulds. In the earlier phase of their life cycle they glide over the forest floor feeding on decaying vegetation: a slime mould in this stage of its life is like a patch of living snot. It looks like a mixture of an amoeba and a fungus. Many people might regard this fascinating organism as one of nature’s less appealing creations. In 2005 Quentin Wheeler and Kelly Miller named a series of slime mould–consuming beetles after President George W. Bush and some prominent members of his cabinet: Agathidium bushi, A. rumsfeldi and A. cheneyi. The press was tempted to draw a rather obvious conclusion from this. However, Quentin Wheeler assured me that he had been a Republican all his life, and that he was very fond of slime beetles. After all, in a work describing some sixty-five beetles he had named another species for his wife, and one after the Dark Lord of Sith, Darth Vader himself (A. vaderi). The authors were clearly fans of the Star Wars saga as well as the Bush government; the black outfit of A. vaderi was ostensibly reminiscent of the outfit of the Evil One. Not long after the publication of the new species Quentin was sitting in his office, carrying out his job as Keeper of Entomology, when the telephone rang. When he answered the call a voice responded: “This is the President of the United States.” He was about to respond with the usual “Oh yes? Well, this is Darth Vader…” when he realized that it actually was the President of the United States. He and his colleagues, Bush said, were honoured to be so immortalized in the names of beetles. Multum in parvo indeed.
Agathidium vaderi, a small dark beetle named by Quentin Wheeler after Darth Vader, evil eminence of Star Wars
7
* * *
Museum Rocks
* * *
There is nothing really special to look at in a Martian meteorite. A similar-looking piece of igneous rock might be picked up on the Isle of Skye or in Newfoundland. Yet these little fragments of rock have reached the surface of our world from Mars. They have ricocheted out into space, probably when the Martian surface was impacted by another meteorite, and then, after an interplanetary journey that might last for millions of years, they have landed on Earth. They must have survived passage through our own oxygen-rich atmosphere, where most meteorites burn up as “shooting stars”—thin bright flashes that flare and then are gone. In short, their survival is little short of a miracle. Martian meteorites are very rare—there are fewer than forty known specimens in total. They also change hands for thousands of dollars, so the lucky individual who discovers one of these rare stones might make a small fortune, literally out of the blue. They are also hard to recognize. What is required to find them is a place where the meteorites will lie undisturbed and unweathered over hundreds of years, and a pair of sharp and skilful eyes to pick out the precious article from a million other stones. These conditions are met in deserts of two kinds: the arid and the icy. A huge ice sheet receives meteoritic gifts from space, acting like a vast outstretched hand; the slow-moving glacier eventually gives them up again at its melting edge. If a scientist knows just where to go, he can discover natural concentrations of meteorites. Most of them will be the commoner kinds of metallic (nickel-iron) or stony meteorites, but in the Antarctic a few of the precious Martian examples have been recovered, the prize for financing a whole expedition. Martian meteorites have turned up particularly on the edges of the Sahara Desert.
I was driven over the top of the Atlas Mountains southwards to the town of Erfoud, in the Moroccan Anti-Atlas, where some of the latest finds have been collected. Ibrahim Tahiri runs a private museum on the edge of this small desert town, which comprises a few streets of undistinguished white buildings surrounding the traditional market, or souk. The new museum is a smart new warehouse full of fine cases and stands showing off a beautiful collection of fossils: giant trilobites and starfish enough to make a palaeontologist weak with acquisitive lust. Ibrahim Tahiri travels to the big rock and fossil show in Houston and knows exactly what a good specimen will make on the open market. He will greet you with a ready smile and proudly show off his treasures: he refuses to sell the cream of his collection displayed in the museum. Tahiri has also claimed new discoveries of Martian meteorites.
It is necessary to drive far out into the desert to see some of the places where meteorites have been found. Low hills display the geology completely; the strata follow one upon the other so that geological time is drawn out blatantly upon the hillside. In the carpet shops of Erfoud the piles of richly coloured rugs follow the same principles of simple stratigraphy. Between the hills, the low ground is often an almost flat plain composed of stony desert, not a tree or a bush in sight. Some areas are covered by migrating sand dunes, so creating a miniature version of the dune fields that cover huge tracts of the true Sahara Desert to the south. But the meteorites are collected on the arid wastes of stony desert: cheerless places that often seem to stretch onwards to infinity. I was curiously reminded of Thomas Hardy’s description of Egdon Heath in Return of the Native: “like man, slighted and enduring, and withal singularly colossal and mysterious in its swarthy monotony.” But, unlike anywhere in Wessex, by midday the reg shimmers in the heat, dissolving in the distance into a glassy mirage. The stony desert “pavement” comprises countless small rocks—and in some places they all look like meteorites. They are painted with desert varnish, a thin covering of iron and manganese that burnishes them purple-black. Some stones become pitted on the surface and then look superficially like nickel-iron meteorites—the class that includes some of the largest bodies to reach the Earth from space, but also many more commonplace examples. I am amazed that the local meteorite hunters can spot the difference between the stones and the meteorites—especially since some of the older meteorites have become secondarily varnished. But there are scouts out in the wasteland who scour the surface of the ground for precious exceptions to the common pebble. One of the most astonishing phenomena of the desert is the way that these Berber detectives suddenly materialize in the middle of nowhere. As the field party inspects an outcrop, a lanky figure dressed in a loose-fitting and frequently ragged robe will suddenly step out from behind the cover of a saltbush. He will lope towards the party at his leisure, and then produce an ancient cloth bag containing treasures, smiling enthusiastically all the while and exposing one or two surviving teeth. Although there will be trilobites and other fossils, pride of place will go to the meteorites he has managed to find among the millions of undistinguished stones. Some of them will be genuine. If your interpreter asks the Berber how long he has been out in the desert, the reply will come back “Many days,” accompanied by a vague wave in the direction of distant hills. But anything of real worth will find its way back to Tahiri. Even in the remoter parts of Morocco the middleman reigns supreme.
I have known a succession of meteorite experts at the Natural History Museum. The senior member, Bob Hutchison—familiar to many as “Hutch”—was a short, bearded Scotsman with an infectious, barking laugh, and an admirable set of principles concerning equal opportunities and the rights of Mankind. His successor, Monica Grady, is a large and sociable (rather than socialist) woman, as prone to wild laughter as Hutch, although equally high in principle, but perhaps from an attachment to the Church rather than to Keir Hardie. She radiates bonhomi
e like a perfume. From its early days the Museum in London was central to meteorite research. Lazarus Fletcher, the Keeper of Mineralogy in 1881, published a pamphlet as a catalogue of the collections; in 1923 George Prior, Fletcher’s successor, published the first of the global catalogues, and the Catalogue of Meteorites has been continually revised ever since. Monica Grady produced the fifth edition in 2000. It lists 22,507 authenticated and catalogued meteorites, which proves just how rare those Martian examples are. All meteorite researchers refer to the Catalogue for their taxonomy—the numbering system that ensures that each meteorite is uniquely identified. The Martian meteorites are known as SNC meteorites, which is shorthand for Shergottites, Nakhlites and Chassignites—the three known varieties of these alien rocks—and one example where an acronym is probably preferable to the original. The ungainly names are derived from the localities where the first typical examples of the meteorite were found: so Chassignite is named after Chassigny, in Haute-Marne, France, where its rare type was discovered in 1815. The Martian signature of these meteorites was suggested more than twenty years ago when it was discovered that the noble gases were present in them in proportions very like those determined by the Viking spacecraft directly from the Martian atmosphere. Since noble gas elements, such as Argon, Xenon and Radon, do not react with other elements, they are like an unshiftable family heirloom, and point the finger firmly at the ancestral home. Subsequent work on isotope ratios of several other elements has also identified a good Martian signature, and few scientists would challenge the origin of these meteorites today.
Monica Grady became scientifically engaged with claims that there were traces of life in the rock samples from Mars. The claims were twofold: that there were fossils in the meteorite samples of tiny rod-shaped objects that might be “bacterial” (so-called nanobacteria, because they were smaller than usual bacterial species), and that the chemical signatures of elements or compounds found in the meteorites were likely to be associated with organic activity. Much brouhaha has been generated by claims that the presence of life on Mars has been fully proven; an endorsement of the theory was even given by President Clinton. A cynic might have said that these spectacular reports might have had something to do with the quest for continued funding by organizations like NASA. A few meteorites have figured prominently in the arguments—like the Shergottite, Catalogue number ALH 84001. Even though Earthling bacteria are a few thousandths of a millimetre long, the minute rod-like structures claimed as nanobacteria from ALH 84001 were a whole lot smaller. The renowned expert on early fossil bacteria Bill Schopf, from the University of California, Los Angeles, declared that he did not believe that the tiny traces were relics of life forms. Then there were discoveries that organic molecules usually associated with biological synthesis could be found in a few SNC meteorites, and their concentrations were greatest inside the meteorite, ruling out contamination. There is nothing unusual about carbon in meteorites—indeed, well-known varieties are called carbonaceous chondrites for reasons that do not require spelling out. It has long been known that these meteorites include traces of amino acids—one of life’s “building blocks.” But these varieties of meteorites are also thought to be very primitive—the kind of basic matter from which the solar system itself was formed. It remains a matter of controversy whether crucial organic molecules for creating life were delivered to Earth by extraterrestrial messengers, or whether the chemistry happened here on the home planet. One of the most exciting things about studying meteorites is that they provide a kind of telescope to see back into the earliest days of the evolution of Earth and its neighbours. Perhaps the wisest option is to keep an open mind about life on Mars, now or in the past, but be very sceptical about those alleged tiny fossils. With more probes beaming back information from the red planet itself, the question should be settled once and for all within the next decade or so.
The Martian meteorite ALH 84001 (which has had some material removed for analysis)
Micrograph of the supposed “fossil” from ALH 84001—not widely accepted as such
Improbable though it may seem, there is a crossover between meteorite studies and my own favourite animals: trilobites. In southern Sweden numerous vast quarries have been opened up to exploit limestones of Ordovician age. These grey rocks have been used extensively as flooring in churches, or, polished, as an ornamental “marble.” They can be distinguished from a hundred and one other ornamental limestones because they carry numerous cross-sections through fossil shells of nautiloid molluscs, which are long cones shaped like the wafers that hold scoops of ice cream; these fossils are divided internally into chambers, so they are very distinctive. The same limestones frequently yield trilobites, which have been used to date the rocks; I know some of them as well as I do my old friends. Because of the great geological stability of eastern Scandinavia, nothing much has happened to these limestones in the 470 million years since they were laid down under a shallow sea; they still carry their fossil evidence in perfect condition. But a trilobite innocently scurrying over the muddy sea floor back in the Ordovician would have had its peace shattered by the arrival of showers of meteorites. Bob Hutchison and his co-workers, Drs. Schmitz and Bridges, have managed to identify “fossil” meteorites in these Ordovician deposits. Because of the way the limestone is quarried, bed by bed, an investigator can crawl over wide, flat areas in some of the quarries, which are effectively exhumed ancient sea floors. Although not exactly common, old meteorites are probably easier to find in these quarries than their equivalents in the Sahara Desert. They show up as dark, walnut-sized blobs on the pale surface of the limestone, and are often surrounded by a rusty halo. Not much of their original chemistry is preserved, but the unusual mineral chromite has survived through hundreds of millions of years to retain an unmistakable signature of the common class of meteorite known as L chondrites. It seems that during the Middle Ordovician the world passed through a massive meteorite “cloud.” Schmitz, Bridges and Hutchison have found evidence of more than twelve meteorite showers at that time. It may well be that this will prove to have been a worldwide phenomenon, although few places are as ideally suited to finding “fossil meteorites” as southern Sweden. Maybe this global meteorite shower will in turn be connected with a dramatic changeover in the trilobites and other animals that happened about the same time, when many new forms appeared in the fossil record…The interesting thing about scientific questions is that one bounces off another like a series of cannoning billiard balls—and just occasionally one finishes up in the pocket.
Mineralogists appear to be rather a sensible lot compared with biologists and palaeontologists. In my attempts to extract oral history from my former colleagues, it proved remarkably easy to get revelations from those who worked upon organisms—whether living or fossil. Quite a few of these anecdotes involved sexual relations between people who I had no idea had had any relations at all, let alone carnal ones. I was already aware that Dry Storeroom No. 1 was a secret trysting place. That dry old sunfish had witnessed many a lubricious episode. I later heard that the attic floor of the old Entomology Block had mattresses deployed to help the entomologists with their studies of the human genome. It seems that the Dark Room was often locked from the inside because of unforeseen developments. Until I interviewed the protagonists, I had no idea of the lustful tendencies of experts on weevils, toads or brachiopods. By contrast, the mineralogists seem to have been altogether better behaved. This may have something to do with the fact that Mineralogy is the smallest department, and the most overseen. Until quite recently, all the post addressed to the scientists was opened in the Keeper’s office, which was certainly inconvenient for anyone trying to arrange a secret assignation. Mineralogists also tend to be the more mainstream scientists. They are the ones that wear the white coats, and hide away in the basement while reading dials from sophisticated machines. Only a few of them have gone mad, and many of them have lived blameless lives in the single-minded pursuit of mineral excellence.
M
inerals do have systematics and taxonomy, just like organisms. Like animals and plants, they are classified into species, although there are far fewer species than in the biological world. The old mineral gallery in the Museum still has the crystal species laid out in an order dictated by their chemistry. The very word “mineral” tends to conjure up a picture of some beautiful and exotic crystal in a display case, but the bulk of minerals are ordinary components of common rocks. A lump of granite is a mass of minerals locked together in a three-dimensional jigsaw. This is an easy fact to verify while one is waiting in a queue in the bank, where polished slabs of granite seem to be invariably displayed on columns and counters. Pale pink or white feldspars speckled among quartz give the rock its dappled texture: there will be three or four mineral species on display. A mineral species has two diagnostic properties: its chemistry and its crystallography. Even if two minerals have the same chemical formula, they can have more than one name if they display more than one fundamentally different crystal form in nature; the simplest example is diamond and graphite, which are both forms of the element carbon, but could scarcely look more different. Because there is a limited list of chemical elements and they can combine with one another only in specified ways, the number of natural mineral species is far from infinite, although there is no sign that science is running out of new discoveries just yet. Many elements are rare in nature, so minerals containing them will also be rare. The appropriately named rare earth elements (with strange names like Yttrium) are very seldom found either singly or in quantity, although they have become very important in geochemistry and can almost be counted atom by atom with modern instruments. Despite their rarity, rare earth elements are useful. Yttrium is used in the high-intensity lamps of cinema projectors, for example. Some elements, like the noble gases we have already met, are so snooty that they won’t combine with anything else except under very exceptional circumstances. By contrast, a few elements—silica, aluminium, oxygen, iron, calcium, carbon, hydrogen—are so abundant that minerals combining some of them in various permutations are found practically everywhere. Silicates—compounds of common quartz—are especially fecund and various because silica molecules can join together in all manner of different ways to form sheets or nets that welcome in the other common elements. Many families of minerals, with names like pyroxenes, feldspars or amphiboles, are silicates that share a common structure. When pure and well formed, a given mineral will usually have a characteristic crystal shape, and often one we find beautiful. This crystalline perfection is a reflection in the hand specimen of the way atoms are stacked and arranged right down at the atomic level. The mineral mica, for example, breaks up into thin sheets if plucked with a fingernail, and the silicate molecules of which it is composed are also arranged in sheets. Common rock salt crystallizes into cubes, and the elements sodium and chlorine of which it is composed are also arranged cubically. The macrocosm mirrors the microcosm.
Dry Storeroom No. 1 Page 24