A short history of nearly everything (67 page)

[24]If you have ever wondered how the atoms determine which 50 percent will die and which 50 percent will survive for the next session, the answer is that the half-life is really just a statistical convenience-a kind of actuarial table for elemental things. Imagine you had a sample of material with a half-life of 30 seconds. It isn’t that every atom in the sample will exist for exactly 30 seconds or 60 seconds or 90 seconds or some other tidily ordained period. Each atom will in fact survive for an entirely random length of time that has nothing to do with multiples of 30; it might last until two seconds from now or it might oscillate away for years or decades or centuries to come. No one can say. But what we can say is that for the sample as a whole the rate of disappearance will be such that half the atoms will disappear every 30 seconds. It’s an average rate, in other words, and you can apply it to any large sampling. Someone once worked out, for instance, that dimes have a half-life of about 30 years.

[25]There are practical side effects to all this costly effort. The World Wide Web is a CERN offshoot. It was invented by a CERN scientist, Tim Berners-Lee, in 1989.

[26]You are of course entitled to wonder what is meant exactly by “a constant of 50″ or “a constant of 100.” The answer lies in astronomical units of measure. Except conversationally, astronomers don’t use light-years. They use a distance called theparsec (a contraction ofparallax andsecond ), based on a universal measure called the stellar parallax and equivalent to 3.26 light-years. Really big measures, like the size of a universe, are measured in megaparsecs: a million parsecs. The constant is expressed in terms of kilometers per second per megaparsec. Thus when astronomers refer to a Hubble constant of 50, what they really mean is “50 kilometers per second per megaparsec.” For most of us that is of course an utterly meaningless measure, but then with astronomical measures most distances are so huge as to be utterly meaningless.

[27]It is KT rather than CT because C had already been appropriated forCambrian. Depending on which source you credit, the K comes either from the GreekKreta or GermanKreide . Both conveniently mean “chalk,” which is also whatCretaceous means.

[28]For those who crave a more detailed picture of the Earth’s interior, here are the dimensions of the various layers, using average figures: From 0 to 40 km (25 mi) is the crust. From 40 to 400 km (25 to 250 mi) is the upper mantle. From 400 to 650 km (250 to 400 mi) is a transition zone between the upper and lower mantle. From 650 to 2,700 km (400 to 1,700 mi) is the lower mantle. From 2,700 to 2,890 km (1,700 to 1,900 mi) is the “D” layer. From 2,890 to 5,150 km (1,900 to 3,200 mi) is the outer core, and from 5,150 to 6,378 km (3,200 to 3,967 mi) is the inner core.

[29]The discovery of extremophiles in the boiling mudpots of Yellowstone and similar organisms found elsewhere made scientists realize that actually life of a type could range much farther than that-even, perhaps, beneath the icy skin of Pluto. What we are talking about here are the conditions that would produce reasonably complex surface creatures.

[30]Of the remaining four, three are nitrogen and the remaining atom is divided among all the other elements.

[31]Oxygen itself is not combustible; it merely facilitates the combus tion of other things. This is just as well, for if oxygen were corn bustible, each time you lit a match all the air around you would bur into flame. Hydrogen gas, on the other hand, is extremely corn bustible, as the dirigibleHindenburg demonstrated on May 6, 193 in Lakehurst, New Jersey, when its hydrogen fuel burst explosive) into flame, killing thirty-six people.

[32]If you have ever been struck by how beautifully crisp and well defined the edges of cumulus clouds tend to be, while other clouds are more blurry, the explanation is that in a cumulus cloud there is a pronounced boundary between the moist interior of the cloud and the dry air beyond it. Any water molecule that strays beyond the edge of the cloud is immediately zapped by the dry air beyond, allowing the cloud to keep its fine edge. Much higher cirrus clouds are composed of ice, and the zone between the edge of the cloud and the air beyond is not so clearly delineated, which is why they tend to be blurry at the edges.

[33]The term means a number of things to different people, it appears. In November 2002, Carl Wunsch of MIT published a report inScience , “What Is the Thermohaline Circulation?,” in which he noted that the expression has been used in leading journals to signify at least seven different phenomena (circulation at the abyssal level, circulation driven by differences in density or buoyancy, “meridional overturning circulation of mass,” and so on)-though all have to do with ocean circulations and the transfer of heat, the cautiously vague and embracing sense in which I have employed it here.

[34]The indigestible parts of giant squid, in particular their beaks, accumulate in sperm whales’ stomachs into the substance known as ambergris, which is used as a fixative in perfumes. The next time you spray on Chanel No. 5 (assuming you do), you may wish to reflect that you are dousing yourself in distillate of unseen sea monster.

[35]There are actually twenty-two naturally occurring amino acids known on Earth, and more may await discovery, but only twenty of them are necessary to produce us and most other living things. The twenty-second, called pyrrolysine, was discovered in 2002 by researchers at Ohio State University and is found only in a single type of archaean (a basic form of life that we will discuss a little further on in the story) calledMethanosarcina barkeri .

[36]To illustrate, humans are in the domain eucarya, in the kingdom animalia, in the phylum chordata, in the subphylum vertebrata, in the class mammalia, in the order primates, in the family hominidae, in the genus homo, in the speciessapiens . (The convention, I’m informed, is to italicize genus and species names, but not those of higher divisions.) Some taxonomists employ further subdivisions: tribe, suborder, infraorder, parvorder, and more.

[37]The formal word for a zoological category, such asphylum orgenus . The plural istaxa .

[38]We are actually getting worse at some matters of hygiene. Dr. Maunder believes that the move toward low-temperature washing machine detergents has encouraged bugs to proliferate. As he puts it: “If you wash lousy clothing at low temperatures, all you get is cleaner lice.”

[39]Actually, quite a lot of cells are lost in the process of development, so the number you emerge with is really just a guess. Depending on which source you consult the number can vary by several orders of magnitude. The figure of ten thousand trillion (or quadrillion) is from Margulis and Sagan, 1986.

[40]Leeuwenhoek was close friends with another Delft notable, the artist Jan Vermeer. In the mid-1660s, Vermeer, who previously had been a competent but not outstanding artist, suddenly developed the mastery of light and perspective for which he has been celebrated ever since. Though it has never been proved, it has long been suspected that he used a camera obscura, a device for projecting images onto a flat surface through a lens. No such device was listed among Vermeer’s personal effects after his death, but it happens that the executor of Vermeer’s estate was none other than Antoni van Leeuwenhoek, the most secretive lens-maker of his day.

[41]An auspicious date in history: on the same day in Kentucky, Abraham Lincoln was born.

[42]Darwin was one of the few to guess correctly. He happened to be visiting Chambers one day when an advance copy of the sixth edition of Vestiges was delivered. The keenness with which Chambers checked the revisions was something of a giveaway, though it appears the two men did not discuss it.

[43]By coincidence, in 1861, at the height of the controversy, just such evidence turned up when workers in Bavaria found the bones of an ancient archaeopteryx, a creature halfway between a bird and a dinosaur. (It had feathers, but it also had teeth.) It was an impressive and helpful find, and its significance much debated, but a single discovery could hardly be considered conclusive.

[44]In 1968, Harvard University Press canceled publication ofThe Double Helix after Crick and Wilkins complained about its characterizations, which the science historian Lisa Jardine has described as “gratuitously hurtful.” The descriptions quoted above are after Watson softened his comments.

[45]Junk DNA does have a use. It is the portion employed in DNA fingerprinting. Its practicality for this purpose was discovered accidentally by Alec Jeffreys, a scientist at the University of Leicester in England. In 1986 Jeffreys was studying DNA sequences for genetic markers associated with heritable diseases when he was approached by the police and asked if he could help connect a suspect to two murders. He realized his technique ought to work perfectly for solving criminal cases-and so it proved. A young baker with the improbable name of Colin Pitchfork was sentenced to two life terms in prison for the murders.

[46]Though Dutch, Dubois was from Eijsden, a town bordering the French-speaking part of Belgium.

[47]Humans are put in the lamely Homimdae. Its members, traditionally called hominids, include any creatures (including extinct ones) that are more closely related to us than to any surviving chimpanzees. The apes, meanwhile, are lumped together in a family called Pongidae. Many authorities believe that chimps, gorillas, and orangutans should also be included in this family, with humans and chimps in a subfamily called Homininae. The upshot is that the creatures traditionally called hominids become, under this arrangement, hominins. (Leakey and others insist on that designation.) Hominoidea is the name of the aue sunerfamily which includes us.

[48]Absolute brain size does not tell you everything-or possibly sometimes even much. Elephants and whales both have brains larger than ours, but you wouldn’t have much trouble outwitting them in contract negotiations. It is relative size that matters, a point that is often overlooked. As Gould notes, A.africanus had a brain of only 450 cubic centimeters, smaller than that of a gorilla. But a typicalafricanus male weighed less than a hundred pounds, and a female much less still, whereas gorillas can easily top out at 600 pounds (Gould pp. 181-83).

[49]One possibility is that Neandertals and Cro-Magnons had different numbers of chromosomes, a complication that commonly arises when species that are close but not quite identical conjoin. In the equine world, for example, horses have 64 chromosomes and donkeys 62. Mate the two and you get an offspring with a reproductively useless number of chromosomes, 63. You have, in short, a sterile mule.