A short history of nearly everything

Perhaps the most extraordinary survival yet found was that of a Streptococcus bacterium that was recovered from the sealed lens of a camera that had stood on the Moon for two years. In short, there are few environments in which bacteria aren’t prepared to live. “They are finding now that when they push probes into ocean vents so hot that the probes actually start to melt, there are bacteria even there,” Victoria Bennett told me.

In the 1920s two scientists at the University of Chicago, Edson Bastin and Frank Greer, announced that they had isolated from oil wells strains of bacteria that had been living at depths of two thousand feet. The notion was dismissed as fundamentally preposterous-there was nothing to live on at two thousand feet-and for fifty years it was assumed that their samples had been contaminated with surface microbes. We now know that there are a lot of microbes living deep within the Earth, many of which have nothing at all to do with the organic world. They eat rocks or, rather, the stuff that’s in rocks-iron, sulfur, manganese, and so on. And they breathe odd things too-iron, chromium, cobalt, even uranium. Such processes may be instrumental in concentrating gold, copper, and other precious metals, and possibly deposits of oil and natural gas. It has even been suggested that their tireless nibblings created the Earth’s crust.

Some scientists now think that there could be as much as 100 trillion tons of bacteria living beneath our feet in what are known as subsurface lithoautotrophic microbial ecosystems-SLiME for short. Thomas Gold of Cornell has estimated that if you took all the bacteria out of the Earth’s interior and dumped it on the surface, it would cover the planet to a depth of five feet. If the estimates are correct, there could be more life under the Earth than on top of it.

At depth microbes shrink in size and become extremely sluggish. The liveliest of them may divide no more than once a century, some no more than perhaps once in five hundred years. As the Economist has put it: “The key to long life, it seems, is not to do too much.” When things are really tough, bacteria are prepared to shut down all systems and wait for better times. In 1997 scientists successfully activated some anthrax spores that had lain dormant for eighty years in a museum display in Trondheim, Norway. Other microorganisms have leapt back to life after being released from a 118-year-old can of meat and a 166-year-old bottle of beer. In 1996, scientists at the Russian Academy of Science claimed to have revived bacteria frozen in Siberian permafrost for three million years. But the record claim for durability so far is one made by Russell Vreeland and colleagues at West Chester University in Pennsylvania in 2000, when they announced that they had resuscitated 250-million-year-old bacteria called Bacillus permians that had been trapped in salt deposits two thousand feet underground in Carlsbad, New Mexico. If so, this microbe is older than the continents.

The report met with some understandable dubiousness. Many biochemists maintained that over such a span the microbe’s components would have become uselessly degraded unless the bacterium roused itself from time to time. However, if the bacterium did stir occasionally there was no plausible internal source of energy that could have lasted so long. The more doubtful scientists suggested that the sample may have been contaminated, if not during its retrieval then perhaps while still buried. In 2001, a team from Tel Aviv University argued that B. permians were almost identical to a strain of modern bacteria, Bacillus marismortui, found in the Dead Sea. Only two of its genetic sequences differed, and then only slightly.

“Are we to believe,” the Israeli researchers wrote, “that in 250 million years B. permians has accumulated the same amount of genetic differences that could be achieved in just 3-7 days in the laboratory?” In reply, Vreeland suggested that “bacteria evolve faster in the lab than they do in the wild.”

Maybe.

It is a remarkable fact that well into the space age, most school textbooks divided the world of the living into just two categories-plant and animal. Microorganisms hardly featured. Amoebas and similar single-celled organisms were treated as proto-animals and algae as proto-plants. Bacteria were usually lumped in with plants, too, even though everyone knew they didn’t belong there. As far back as the late nineteenth century the German naturalist Ernst Haeckel had suggested that bacteria deserved to be placed in a separate kingdom, which he called Monera, but the idea didn’t begin to catch on among biologists until the 1960s and then only among some of them. (I note that my trusty American Heritage desk dictionary from 1969 doesn’t recognize the term.)

Many organisms in the visible world were also poorly served by the traditional division. Fungi, the group that includes mushrooms, molds, mildews, yeasts, and puffballs, were nearly always treated as botanical objects, though in fact almost nothing about them-how they reproduce and respire, how they build themselves-matches anything in the plant world. Structurally they have more in common with animals in that they build their cells from chitin, a material that gives them their distinctive texture. The same substance is used to make the shells of insects and the claws of mammals, though it isn’t nearly so tasty in a stag beetle as in a Portobello mushroom. Above all, unlike all plants, fungi don’t photosynthesize, so they have no chlorophyll and thus are not green. Instead they grow directly on their food source, which can be almost anything. Fungi will eat the sulfur off a concrete wall or the decaying matter between your toes-two things no plant will do. Almost the only plantlike quality they have is that they root.

Even less comfortably susceptible to categorization was the peculiar group of organisms formally called myxomycetes but more commonly known as slime molds. The name no doubt has much to do with their obscurity. An appellation that sounded a little more dynamic-“ambulant self-activating protoplasm,” say-and less like the stuff you find when you reach deep into a clogged drain would almost certainly have earned these extraordinary entities a more immediate share of the attention they deserve, for slime molds are, make no mistake, among the most interesting organisms in nature. When times are good, they exist as one-celled individuals, much like amoebas. But when conditions grow tough, they crawl to a central gathering place and become, almost miraculously, a slug. The slug is not a thing of beauty and it doesn’t go terribly far-usually just from the bottom of a pile of leaf litter to the top, where it is in a slightly more exposed position-but for millions of years this may well have been the niftiest trick in the universe.

And it doesn’t stop there. Having hauled itself up to a more favorable locale, the slime mold transforms itself yet again, taking on the form of a plant. By some curious orderly process the cells reconfigure, like the members of a tiny marching band, to make a stalk atop of which forms a bulb known as a fruiting body. Inside the fruiting body are millions of spores that, at the appropriate moment, are released to the wind to blow away and become single-celled organisms that can start the process again.

For years slime molds were claimed as protozoa by zoologists and as fungi by mycologists, though most people could see they didn’t really belong anywhere. When genetic testing arrived, people in lab coats were surprised to find that slime molds were so distinctive and peculiar that they weren’t directly related to anything else in nature, and sometimes not even to each other.

In 1969, in an attempt to bring some order to the growing inadequacies of classification, an ecologist from Cornell University named R. H. Whittaker unveiled in the journal Science a proposal to divide life into five principal branches-kingdoms, as they are known-called Animalia, Plantae, Fungi, Protista, and Monera. Protista, was a modification of an earlier term, Protoctista, which had been suggested a century earlier by a Scottish biologist named John Hogg, and was meant to describe any organisms that were neither plant nor animal.

Though Whittaker’s new scheme was a great improvement, Protista remained ill defined. Some taxonomists reserved it for large unicellular organisms-the eukaryotes-but others treated it as the kind of odd sock drawer of biology, putting into it anything that didn’t fit anywhere else. It included (depending on which text you consulted) slime molds, amoebas, and even seaweed, among much else. By one calculation it contained as many as 200,000 different species of organism all told. That’s a lot of odd socks.

Ironically, just as Whittaker’s five-kingdom classification was beginning to find its way into textbooks, a retiring academic at the University of Illinois was groping his way toward a discovery that would challenge everything. His name was Carl Woese (rhymes with rose), and since the mid-1960s-or about as early as it was possible to do so-he had been quietly studying genetic sequences in bacteria. In the early days, this was an exceedingly painstaking process. Work on a single bacterium could easily consume a year. At that time, according to Woese, only about 500 species of bacteria were known, which is fewer than the number of species you have in