The Universe Within (30 page)

The relative numbers of the atoms in the
human body were taken from Robert W. Sterner and James J. Elser,
Ecological Stoichiometry: The Biology of Elements from Molecules to the Biosphere
(Princeton, N.J.: Princeton University Press, 2002), chap. 1. This is of course not a true chemical formula, as the ratios of elements in us compose not a single unique molecule, like a crystal of salt, but a body consisting of numerous different kinds of them.

The notion of a tree of life that connects all creatures living and extinct is one of the insights of the
Darwinian revolution. It makes specific and testable predictions and allows us to formulate hypotheses. Background discussion of these methods written for a general audience is found in
Dawkins’s
Ancestor’s Tale
. For those who wish a treatment written for practitioners, try E. O. Wiley et al.,
The Compleat Cladist: A Primer of Phylogenetic Procedures
, special publication no. 19 (Lawrence: University of Kansas, Museum of Natural History, 1991),
http://www.archive.org/​stream/​compleatcladistp00wile#page/​n5/​mode/​2up
. To get a real taste for the discipline with its applications and vigorous debates, try some of the journals in the field:
Cladistics
and
Systematic Biology
.

The story of
Henrietta Leavitt’s work is published in E. C. Pickering, “Periods of 25 Variable Stars in the Small Magellanic Cloud,”
Harvard College Observatory Circular
173 (1912): 1–3. The story of her work, and that of the other women in the observatory, is in Nina Byers and Gary Williams, eds.,
Out of Shadows: Contributions of Twentieth-Century Women to Physics
(New York: Cambridge University Press, 2006); and Jacob Darwin Hamblin,
Science in the Early Twentieth Century: An Encyclopedia
(Santa Barbara, Calif.: ABC-CLIO, 2005), 181–84.

General discussion of the big bang and its consequences can be found in Krauss,
Atom;
Tyson and Goldsmith,
Origins;
Simon Singh,
Big Bang: The Origin of the Universe
(New York: HarperCollins, 2005); and Steven Weinberg,
The First Three Minutes
, updated ed. (New York: Basic Books, 1993).

Operation Ivy Mike, the first test of the Teller-Ulam device, is described in Richard Rhodes,
Dark Sun: The Making of the Hydrogen Bomb
(New York: Simon & Schuster, 1995).

In the days since the “nebular hypothesis” of
Swedenborg,
Kant, and
Laplace, the origin of the planets of the
solar system has been an active area of research, discovery, and debate. General background can be found in Tyson and Goldsmith,
Origins
. A general review of the dynamics of the
formation of Earth is found in R. M. Canup, “Accretion of the Earth,”
Philosophical Transactions
of the Royal Society A
366 (2008): 4061–75. For those with a quantitative background who want to immerse themselves in the field by reading original scientific papers, go to the main scientific journal of the field,
Icarus: The International Journal of Solar System Studies
, the official publication of the Division of Planetary Sciences of the American Astronomical Society.

Harry McSween has written wonderful books on the solar system, meteoritics, and
cosmochemistry. See in particular
Stardust to Planets: A Geological Tour of the Solar System
(New York: St. Martin’s Press, 1993). For an excellent review of the dynamics of the solar system, see J. Kelly Beatty, Carolyn C. Petersen, and Andrew Chaikin,
The New Solar System
, 4th ed. (Cambridge, Mass.: Sky Publishing, 1999).

The field of cosmochemistry is concerned with the chemical analysis of meteors, lunar rocks, and other extraterrestrial materials. On November 29, 2011, the
Proceedings of the National Academy of Sciences
(
PNAS
) ran a special issue with a number of excellent reviews. The opening review is a useful overview of the field and the special issue: G. MacPherson and M. H. Thiemens, “Cosmochemistry: Understanding the Solar System Through Analysis of Extraterrestrial Materials,”
PNAS
108 (2011): 19130–34.

Studies of the
age of Earth have, themselves, a rich history. A source now several decades old but a resource for history, detail, and method, is G. Brent Dalrymple,
The Age of the Earth
(Stanford, Calif.: Stanford University Press, 1991). For a more recent treatment, see G. B. Dalrymple, “The Age of the Earth in the Twentieth Century: A Problem (Mostly) Solved,” in
The Age of the Earth: From 4004
B.C.
to
A.D.
2002
, Geological Society, London, Special Publication 190, ed. C. L. E. Lewis and S. J. Knell (London: Geological Society, 2001), 205–21. This special publication from the London Geological Society contains a veritable feast of papers on the age of Earth, the history of this field of study, and the methods used.

Zircons are magnificent windows into early Earth. See J. W. Valley, W. H. Peck, and E. M. King, “Zircons Are Forever,”
Outcrop
, University of Wisconsin-Madison Geology Alumni Newsletter (1999), 34–35. For a scientific paper on this, see S. A. Wilde et al., “Evidence from Detrital Zircons for the Existence of Continental Crust and Oceans on the Earth 4.4 Gyr Ago,”
Nature
409 (2001): 175–78. For a general treatise on the hunt for and meaning of the
oldest rocks on the planet, see Martin Van Kranendonk, R. Hugh Smithies, and Vickie C. Bennett, eds.,
Earth’s Oldest Rocks
(Boston: Elsevier, 2007). That volume has an enormous amount of information written by and for specialists in the field.

Geologists tell time in rocks in two ways: relatively and absolutely. See Doug Macdougall,
Nature’s Clocks: How Scientists Measure the Age of Almost Everything
(Berkeley: University of California Press, 2008). Relative time is a matter of understanding the relationships between different layers—layers above are generally younger than those below. The situation gets challenging
when the layers are highly altered. Piecing together the layer history comes from understanding the faults and movements that shifted rocks and layers about.

Calculating absolute time in rocks and minerals depends on understanding the
radioactive
decay of atoms. Some atoms have an unstable configuration of electrons, neutrons, and protons, causing them to lose or gain components. As they do this, their atomic weights can change, and they become new forms. The important point is that this transformation happens at rates that are physical constants, known as the half-life. The half-life of an atom is the time required for one-half of a sample to decay, or transform, into its daughters. If you know the amounts of parent atoms, daughter atoms, and the half-life, then you can calculate the time that the atoms have been decaying. A number of atoms are useful to geologists:
uranium 238, argon 39, and
carbon 14, for example. In general, you try to match atoms for the job: atoms with the slowest decay rates are useful for the
oldest rocks, whereas those that decay faster are useful for more recent ones. Uranium 238, with its long half-life, is useful for questions about the most ancient phases of Earth. Carbon 14 has such a rapid decay rate it is useful for more recent events, such as those of human history and culture.

In
zircons, such as those from the
Jack Hills, the isotopes (atomic versions) of uranium and lead are most useful. Uranium 238 decays into a stable daughter isotope,
lead 206, with a half-life of 4.5 billion years. When uranium was incorporated in the zircon when it was formed, the clock started ticking: the slow transformation to lead 206 began. Looking at that zircon now, we make the reasonable assumption that all of the lead 206 has come from the decay of uranium. Knowing the ratios of parent and daughter isotopes and the half-life allows the age of the zircon to be calculated.

A general timescale for the major events in the history of the solar system and Earth is in F. Albarede, “Volatile Accretion History of the Terrestrial Planets and Dynamic Implications,”
Nature
461 (2009): 1227–33.

We’ve witnessed a number of different ideas about where the
water of the planet came from. For a long time, it was thought that the main source was icy
comets. That hypothesis was challenged when cometary water was sampled during a
satellite visit to
Hale-Bopp as it came close to Earth. These measurements revealed that the comet’s water had a different chemical signature than the water of Earth’s oceans. The comet hypothesis was in trouble until measurements were taken more recently of another comet: this one,
Hartley 2, has more Earth-like water. Now a number of potential sources exist, and none are mutually exclusive: comets,
asteroids, even squeezed or condensed from the constituents of early Earth. Reviews of the evidence are in N. H. de Leeuw et al., “Where on Earth Has Our Water Come From?,”
Chemical Communications
46 (2010): 8923–25; M. J. Drake and H. Campins, “
Origin of Water in the Terrestrial Planets,”
Proceedings of the International Astronomical Union
1, no. S229 (2006): 381–94. The discovery of ocean-like water on a
Kuiper
belt comet, Hartley-2, is described in P. Hartogh et al., “Ocean-Like
Water in the Jupiter-Family Comet 103P/Hartley 2,”
Nature
478 (2011): 218–20. For images of potential water in the polar craters of Mercury, see
NASA’s website:
http://www.nasa.gov/​mission_pages/​messenger/​multimedia/​messenger_orbit_image20120322_3.html
.

For the
formation of the different planets of the solar system, and the relationships among them, see R. M. Canup, “
Origin of Terrestrial Planets and the Earth-Moon System,”
Physics Today
, April 2004, 56–62.

The origin of the moon has been the subject of a large number of scientific papers in recent years. For a sampling, with references, see R. M. Canup, “Formation of the Moon,”
Annual Review of Astronomy and Astrophysics
42 (2004): 441–75; R. M. Canup and K. Righter, eds.,
Origin of the Earth and Moon
(Tucson: University of Arizona Press, 2000); Canup, “Origin of Terrestrial Planets and the Earth-Moon System.”

For a history of the ways we keep time, see the work of Anthony Aveni, in particular
Empires of Time: Calendars, Clocks, and Cultures
(Boulder: University of Colorado Press, 2002).

The idea that clocks are embedded throughout the natural world is explored in detail in Macdougall,
Nature’s Clocks
.

A wonderful book on clocks, time, and our
perception of time is Robert Levine,
A Geography of Time: On Tempo, Culture, and the Pace of Life
(New York: Basic Books, 1998).
Michel Siffre’s cave experience is documented in his personal account,
Beyond Time
(New York: McGraw-Hill, 1964).

The story of
Curt Richter’s life’s work can be found in his biographical memoir published by the National Academy of Sciences, in
Biographical Memoirs
, vol. 65 (Washington, D.C.: National Academy Press, 1994),
http://www.nap.edu/​catalog.php?record_id=4548
.

The story of
Seymour Benzer and the discovery of the molecular basis for
circadian clocks, among other things, is in Jonathan Weiner’s wonderful
Time, Love, and Memory: A Great Biologist and His Quest for the Origins of Behavior
(New York: Vintage, 2000).

The starting point for learning more about biological clocks is John D. Palmer’s readable and often funny
The Living Clock
(Oxford: Oxford University Press, 2002). If you want more detail from the primary literature itself, then proceed to the papers in the following paragraphs.

The Benzer lab’s discovery of clock
mutants is detailed in R. J.
Konopka and S. Benzer, “Clock Mutants of
Drosophila melanogaster
,”
PNAS
68 (1971): 2112–16. The trio of labs that cloned the gene and explored its biological ramifications were Jeffrey Hall’s (Brandeis), Michael Rosbash’s (Brandeis), and
Michael Young’s (Rockefeller). The biology of these circadian clock mutants in diverse creatures is discussed in a number of papers, including Z. S. Sun et al., “RIGUI, a Putative Mammalian Ortholog of the Drosophila Period Gene,”
Cell
90 (1997): 1003–11; H. Tei et al., “Circadian Oscillation of a Mammalian Homologue of the
Drosophila
Period Gene,”
Nature
389 (1997): 512–16; M. W. Young and S. A. Kay, “Time Zones: A Comparative Genetics of Circadian Clocks,”
Nature Reviews Genetics
2 (2001): 702–15; W. Yu and P. E. Hardin, “Circadian Oscillators of
Drosophila
and Mammals,”
Journal of Cell Science
119 (2006): 4793–95; E. E. Hamilton and S. A. Kay, “SnapShot: Circadian Clock Proteins,”
Cell
135 (2008); K. Lee, J. J. Loros, and J. C. Dunlap, “Interconnected Feedback Loops in the
Neurospora
Circadian System,”
Science
289 (2000): 107–10; E. Tauber et al., “Clock Gene Evolution and Functional Divergence,”
Journal of Biological Rhythms
19 (2004): 445–58; D. Bell-Pedersen et al., “Circadian Rhythms from Multiple Oscillators: Lessons from Diverse Organisms,”
Nature Reviews Genetics
6 (2005): 544–56.

The circadian clock and its evolution have been the subjects of a number of excellent reviews and books in the scientific literature. An entrée to this body of work can be found in the following papers: J. Dunlap, “Molecular Basis for Circadian Clocks,”
Cell
96 (1999): 271–90; M. Rosbash, “Implications of Multiple Circadian Clock Origins,”
PLoS Biology
7 (2009): 17–25; S. Panda, J. B. Hogenesch, and S. A. Kay, “Circadian Rhythms from Flies to Human,”
Nature
417 (2002): 329–35.

The similarity of
sleep mechanisms in diverse organisms is discussed in detail in C. Cirelli, “The Genetic and Molecular Regulation of Sleep: From Fruit Flies to Humans,”
Nature Reviews Neuroscience
10 (2009): 549–60; and Panda et al., “Circadian Rhythms from Flies to Human.”