Scientific American June 2009 - UK Edition - Angelfire

76 Pages·2009·12.55 MB·English

by  Scientific American Inc.

Phosphorus Famine Scientific American 10
The Threat to Our Food Supply Guiding Science for Humanity
The
Evolution of
HoUSE
CATS
page 56
June 2009 $5.99 U.S. U.K. £4.10 www.ScientificAmerican.com
Unlikely Suns,
Improbable Planets
Astronomers find new worlds
around surprisingly
small stars
Silent Mutations
Seemingly Trivial DNA
Changes Can Hurt Health
Racetrack Memory
Zooming Magnetic Bits
for 3-D Data Storage
© 2009 SCIENTIFIC AMERICAN, INC.

features ■
scientific american June 2009 ■ Volume 300 number 6
26
astrOnOmY
Improbable Planets
By Michael W. Werner
and Michael A. Jura
Astronomers are finding abundant planets
around stars that are not much bigger than
planets themselves. Also, see page 45:
Donald Goldsmith on what it will take
to see new Earths.
meDicine 34
34 The Price of Silent Mutations
By J. V. Chamary and Laurence D. Hurst
Small changes to DNA sequences that seemingly
should not affect the proteins encoded by genes
are proving to be remarkably important in
human diseases, evolution and biotechnology.
sustainabiLitY
42 Phosphorus: A Looming Crisis
42 48
By David A. Vaccari
This underappreciated element could become
one of the key sustainability issues of our time.
Even as excesses of phosphorus in agricultural
runoff cause dangerous algal blooms, global
reserves of it are depleting rapidly.
Getty Images 48 tSeccieHnntOifLiOcG AY mLeearDicearns H10iP
rt
ki Ha Certain researchers, politicians, business executives On tHe cOVer
d vik and philanthropists have recently demonstrated A brown dwarf star glows dully in the sky of one
n
gk a outstanding commitment to making sure that of its orbiting planets, as imagined by artist
ver: the benefits of new technologies and knowledge Phil Saunders of Space Channel Ltd. Astronomers
o
n c will accrue to humanity. Scientific American long dismissed the idea of planetary systems
o
at gives credit where credit is due. around such small stars as unlikely.
c
1
www.ScientificAmerican.com © 2009 SCIENTIFIC AMERICAN, INC. SCIENTIFIC AMERICAN
mOre features ■ DePartments ■
eVOLutiOn
56 The Taming of the Cat 56
By Carlos A. Driscoll, Juliet Clutton-Brock,
Andrew C. Kitchener and Stephen J. O’Brien
Genetic and archaeological findings hint that
wildcats became the first house cats earlier—and
elsewhere—than previously thought.
infOtecH
64 Data in the Fast Lanes
of Racetrack Memory
By Stuart S. P. Parkin
Devices that slide magnetic bits along nanowire
64
“racetracks” could store information in three-
dimensional microchips. They might eventually
replace nearly all forms of conventional data storage.
GO tO .cOm
in-DePtH rePOrt:
8
tHe science Of beautY q slide show
From human growth hormone to collagen Five Ways Science Is Trying to Keep Your Food Safe
stimulators, we examine the tactics employed to In the wake of salmonella outbreaks, scientists are developing
technologies that could protect against future threats.
enhance beauty and stave off the ravages of aging.
8
60-second science blog
PCs Idling Overnight Waste Billions in Energy Costs
Because nearly half of U.S. workers leave their computers
running overnight, offices rack up an extra $2.8 billion annually
in wasteful electricity bills, according to one tally.
8
news
The First Meteorites Recovered from a Tracked Asteroid
Fragments in the Sudanese desert complete an “asteroid
trifecta”—discovery in space, prediction of the impact site
and recovery of fragments.
8
60-second science Podcast
Caffeine Cuts Workout Pain
New research suggests that caffeine, by keeping you from feel-
ages ing the burn, can help you get more bang for your workout buck.
ourtesy of tktktk tktktkMore at www.scientificamerican.com/sympHonie/getty imjun20098 TThtsohhemleeldi of Hdmagimdreaadnop eyush nssy ehc Ftcaaororc evbetwers iod.n f Ngb N uotehswtfe eormreft sttietohia elri cgahnhect.ries natr eE gayppptliyainn gq ucoemenp huates d
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Scientific American (ISSN 0036-8733), published monthly by Scientific American, Inc., 415 Madison Avenue, New York, N.Y. 10017-1111. Copyright © 2009 by Scientific
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2
SCIENTIFIC AMERICAN © 2009 SCIENTIFIC AMERICAN, INC. June 2009
mOre features ■ DePartments ■
4 From the Editor 7 00 8
5 Letters
7 50, 100 and 150 Years Ago
8 Updates
N s
ews caN
9
0110
■ Kyoto carbon credits are failing.
■ Are Midwestern earthquake faults shutting down?
■ Yanking pathogens out of blood with magnets.
■ Genetic copy variations and disease.
■ Metabolic secrets of the sled dog.
■ Stretching your mouth affects what you hear.
■ Computer-based Conficker worms.
■ Data Points: The future in fusion.
O
piNiON

21 Scientific American Perspectives
■
The inevitable disappointments from stem cells.
22 Sustainable Developments
■
By Jeffrey D. Sachs
Rethinking the global monetary system.
70 Reviews
24 Skeptic
■ Dinochicken. Acts of God.
By Michael Shermer Nature’s masterpiece.
Why people believe that invisible agents
72 Ask the Experts
control the world.
What causes albinism and are there
25 Anti Gravity
■ treatments for it?
By Steve Mirsky Why do two great tastes sometimes
Maybe proof of evolution is not taste great together?
as close as the nearest kennel.
24
72
22
3
www.ScientificAmerican.com © 2009 SCIENTIFIC AMERICAN, INC.
from the editor ■
Inspirational Orbits
Astronomers are finding new planets; humanitarians are improving this one
The year 1609 was noteworthy them. Astronomers Michael W. Werner
for two astronomical mile- and Michael A. Jura have more in their ar-
stones. That was when Gali- ticle start ing on page 26, including why the
leo built his first telescopes existence of these unlikely planetary sys-
and began his meticulous tems might imply that the universe is chock-
study of the skies. Within months he dis- full of planets.
covered the four major satellites of Jupiter, This year also marks the 50th anniver-
saw that Venus (like our moon) has illumi- sary of the famous “Two Cultures” lecture
nated phases and confirmed earlier obser- by C. P. Snow, the English physicist and
vations of sunspots—all evidence that un- novelist. Snow’s speech, and his later books
dermined the Aristotelian model of an un- that elaborated on it, argued that commu-
changing, Earth-centered cosmos. nication and respect between the sciences
During that same year, Johannes Kepler and humanities had broken down. Liter-
published Astronomia Nova, which con- ary intellectuals, he said, were often non-
tained his detailed calculation of the orbit plussed at their own ignorance of basic sci-
of Mars. It also established the first two ence and yet would be aghast at a scientist
laws of planetary motion: that unfamiliar with Shakespeare;
planets follow ellipti- conversely, scientists
cal orbits, with the were more likely to
sun at one fo-
Among Our new worldS
cus, and that
await around
Contributors planets sweep
the stars
through equal
least likely
Laurence D. Hurst areas of their
to be suns.
is professor of evolutionary genetics orbits in a giv-
at the University of Bath in England
and a Royal Society Research Fellow en interval. have some school-
specializing in the study of genomes Small wonder, ing in the arts. This
and chromosomes.
then, that when the Unit- asymmetrical hostility
MicHaeL a. Jura ed Nations General Assembly de- hurt society, Snow maintained, be-
is professor of astronomy at the clared an International Year of Astronomy cause it impeded the embrace of what sci-
University of California, Los Angeles,
where he investigates exoplanets to promote the wider appreciation of the ence and technology could do to eliminate
and the astrophysics of low-density science, it selected 2009, the quadricenten- poverty and inequality.
environments.
nial of those standout accomplishments Even today critics disagree about wheth-
stuart s. P. Parkin (among many) by Galileo and Kepler that er Snow’s thesis is better seen as controver-
manages the magnetoelectronics informally founded modern astronomy. sial or clichéd. If the “two cultures” is a
group at the IBM Almaden Research
Center and is a consulting professor Currently astronomers can look beyond problem, however, some leaders—not just
of applied physics at Stanford the familiar planets and moons to entirely in science but also industry, government
University.
new systems of worlds around other stars. and nongovernmental organizations—are
rtadtDeohniarmnede mvS csh ttiefaesDon svtr teh waamnelo. s a adr vnInkennaedpsed atcodi rwtcc tusemaipttaehaern ocn Nieeft nA TomgeSf iicAcsnhis evonieoinolr,n liseonsyn.ggsv y-ai -t Akomrefnsec o toaIhwng ewnsns ie trezh ixbetaedtotr , dat Gbhiseuaoissltl i,a wl ereta eohpcr elhoea rntof aoeKnltuelesyn .po dOlswe trbnae ylswny di toatessu lh edlaadsitnc s hocd3aopf4vuvi4ce-l oioapnpvfeg reps ircwltciiyeeoh.dn maT tttii hofitnhi cgsie mkiymtn pcsoorapnownetvc lhteeto, da w wcgeuneei tllsaalhu-rr breloeye u c.it norTh gnaSh stcea ttiyrnheu daenc rtftpeiri rvudfoeioilstcys-- n miller (planets and stars)
o
iMs picroHjeacet Lsc iWen. tWiset fronr NeArSA’s Spitzer eryA to r ethceenirt wanodrk s.urprising trend is the ap- Aremcoegrnicizaen a 1fe0w h oonf othre rmol.l , we are proud to■ Rennie); r
Sfopra acset rToenleosmcoyp aen adn pdh cyhsiiecsf sacti e ntist parent abundance of planets turning up rsen (
the NASA/Caltech Jet Propulsion close to very small stars—suns that may not John rennie n la
Laboratory. be much larger than the planets circling editor in chief flyn
4
Scientific AmericAn © 2009 SCIENTIFIC AMERICAN, INC. June 2009
LetterS ■
[email protected]
®
naked singularities serious Games Beef Production
■ ■
Established 1845
EDITOR IN CHIEF: John Rennie
EXECUTIVE EDITOR: Mariette DiChristina
MANAGING EDITOR: Ricki L. Rusting
CHIEF NEWS EDITOR: Philip M. Yam
SENIOR WRITER: Gary Stix “Game designers are increasingly
EDITORS: Peter Brown, Davide Castelvecchi,
Graham P. Collins, Mark Fischetti, aware of games’ power to influence
Steve Mirsky, Michael Moyer, George Musser,
Christine Soares, Kate Wong neural pathway formation.”
CONTRIBUTING EDITORS: Mark Alpert,
Steven Ashley, Stuart F. Brown, W. Wayt Gibbs, —Noah Falstein GrEEnbraE, Calif.
Marguerite Holloway, Christie Nicholson,
Michelle Press, Michael Shermer, Sarah Simpson
MANAGING EDITOR, ONLINE: Ivan Oransky FEBRUARY 2009
NEWS EDITOR, ONLINE: Lisa Stein
ASSOCIATE EDITORS, ONLINE: David Biello,
Larry Greenemeier ■ end without horizons? behavior of light paths in general relativity. Aspects
NEWS REpORTERS, ONLINE: Coco Ballantyne,
Jordan Lite, John Matson In “Naked Singularities,” Pankaj S. such as the causal structure of spacetime and the
ART DIRECTOR, ONLINE: Ryan Reid Joshi argues that models for stellar col- global properties of light cones are crucial factors.
lapse can produce naked singularities, or These factors arise mainly as a result of the nonlinear-
ART DIRECTOR: Edward Bell singularities without the event horizon ity of Einsteinian equations, and detailed studies of
SENIOR ASSOCIATE ART DIRECTOR: Mark Clemens
ASSISTANT ART DIRECTOR: Johnny Johnson that surrounds a black hole. According to collapse models imply that gravity can be arbitrarily
ASSISTANT ART DIRECTOR: Jen Christiansen quantum theory, black holes emit thermal large and dense in a stellar collapse but still not ines-
pHOTOGRApHY EDITOR: Monica Bradley
pRODUCTION EDITOR: Richard Hunt radiation and evaporate because of the capable. Large density or curvature values do not
separation of particle-antiparticle pairs necessarily mean an event horizon is present.
COpY DIRECTOR: Maria-Christina Keller near their event horizon. Will a naked sin- In Newtonian gravity, density is the sole param-
COpY CHIEF: Daniel C. Schlenoff gularity ever disappear? eter that determines the behavior of a gravitational
COpY AND RESEARCH: Michael Battaglia,
Aaron Shattuck, Rachel Dvoskin, Aaron Fagan, Daniel Chamudot field. But in general relativity, there are 10 gravita-
Michelle Wright, Ann Chin
Riverdale, N.Y. tional metric potentials, and these elements can and
do give rise to many novel features for gravity and its
EDITORIAL ADMINISTRATOR: Avonelle Wing
SENIOR SECRETARY: Maya Harty If an event horizon has an extreme but interactions in the universe.
finite spacetime curvature and gravity,
ASSOCIATE pUBLISHER, pRODUCTION: and in a singularity these are infinite, ■ Gaming the neural system
William Sherman
MANUFACTURING MANAGER: Janet Cermak how can there be any path between a low- In “Childhood Recovered” [News
ADVERTISING pRODUCTION MANAGER: Carl Cherebin gravity and curvature region and a singu- Scan], Gary Stix notes that adult amblyo-
pREpRESS AND QUALITY MANAGER: Silvia De Santis
pRODUCTION MANAGER: Christina Hippeli larity without passing through a horizon? pia patients have achieved substantial im-
CUSTOM pUBLISHING MANAGER: Lloyd Anderson provements after video game–like exercis-
Madelyn Keyes-Milch
Villa Park, Ill. es. He states that “Grand Theft Auto IV or
Board of advisers Medal of Honor may retrain the brain in
JoshI RePlIes: Regarding Chamudot’s question, the ways its developers never imagined.”
Rita R. Colwell
Distinguished Professor, University of Maryland event horizon is a crucial factor in the evaporation of I found this assertion personally ironic:
College Park and Johns Hopkins Bloomberg School a black hole through quantum effects, but in a naked I was the initial designer and executive pro-
of Public Health
singularity case, it is still possible for the event horizon ducer on the Normandy Beach game that
danny hillis
to disappear or evaporate through quantum or classi- later became the first Medal of Honor and
Co-chairman, Applied Minds
cal processes. The effects of quantum gravity, for ex- am now working primarily in games that
Vinod Khosla
Founder, Khosla Ventures ample, could generate a huge negative pressure, have a function beyond entertainment. De-
M. GRanGeR MoRGan causing the star to emit most of its mass in late col- signers are increasingly aware of games’
Professor and Head of Engineering and Public lapse stages. Further, classical processes such as power to influence neural pathway forma-
Policy, Carnegie Mellon University
powerful shock formations caused by inhomogene- tion and have designed programs to build
lisa Randall
ities in matter densities near the naked singularity cognitive reserve through brain training, to
Professor of Physics, Harvard University
could cause it to explode. treat attention-deficit hyperactivity disor-
GeoRGe M. whitesides
Professor of Chemistry, Harvard University With respect to Anderson’s letter, it is not just the der and to help patients with Parkinson’s
local density or curvature values that determine the disease. We may not have thought of those
5
www.ScientificAmerican.com © 2009 SCIENTIFIC AMERICAN, INC. SCIENTIFIC AMERICAN
LetterS ■
applications years ago, but we are learning grown in CAFOs produces aggregate carbon dioxide
to rewire our brains to do so now! (CO2) numbers that are at least one half to one third
®
Noah Falstein as large as those from the Food and Agriculture Or-
Greenbrae, Calif. ganization, which found that livestock contribute
Established 1845
about 18 percent of world greenhouse emissions.
Cows and Carbon
■ Pastoral systems can sometimes be responsible
“The Greenhouse Hamburger,” by Na- for producing more CO2 than CAFOs, mainly because pMRAENSAIDGEINNGT: D SIRteEvCeTnO YRe,e I N TERNATIONAL: Kevin Hause
than Fiala, argues that beef production is many communities, mostly in Latin America, require VICE pRESIDENT: Frances Newburg
a major cause of global warming. But the deforestation for pastoral land. And CAFO cows live
data and articles Fiala cites assume that only about one year before slaughter. In the July 1999 MANAGING DIRECTOR, CONSUMER MARkETING:
Christian Dorbandt
the total amount of beef produced is all Ecological Economics, Susan Subak did find that a ASSOCIATE DIRECTOR, CONSUMER MARkETING:
grown in concentrated animal feeding op- good pastoral system generates just more than half Anne Marie O’Keefe
SENIOR MARkETING MANAGER/RETENTION:
erations (CAFOs). In my beef operation, the CO2 of a feedlot, but she assumed that the pasto- Catherine Bussey
cows never eat or see a pound of harvested ral animals live for just less than three years. If the FULFILLMENT AND DISTRIBUTION MANAGER:
Rosa Davis
grain. They spend their lives (average of 10 animals are allowed to live more than three times as
years) eating grass from native pasture- long, the difference narrows considerably. MANAGING DIRECTOR, ONLINE: Michael Harbolt
land. I am not the exception; all my neigh- My work is not intended to convert people to
bors raise their cattle the same way. vegetarianism, only to help them understand how VICE pRESIDENT AND pUBLISHER:
Bruce Brandfon
William Fogarty consumption choices can have major effects on the DIRECTOR, GLOBAL MEDIA SOLUTIONS:
Jeremy A. Abbate
oakdale, Calif. environment. Given the incredible quantities of meat
VICE pRESIDENT, MARkETING AND SALES
Americans and others eat, even a small decrease in DEVELOpMENT: Michael Voss
beef consumption (to, say, three or four times a SALES DEVELOpMENT MANAGER: David Tirpack
SALES REpRESENTATIVES: Jeffrey Crennan,
week) can have a big impact. Thomas Nolan, Stan Schmidt
■ Car Crash pROMOTION MANAGER: Diane Schube
In discussing the woes of the U.S. auto
VICE pRESIDENT, FINANCE, AND
industry in “Transforming the Auto In- GENERAL MANAGER: Michael Florek
dustry” [Sustainable Developments], Jef- BUSINESS MANAGER: Marie Maher
frey Sachs misses the essential failing that
DIRECTOR, SpECIAL pROJECTS: Barth David Schwartz
has led to decline of its long-term market
AVERAGE AMERICAN’S annual beef diet share and sales volume: mediocre cars. DIRECTOR, ANCILLARY pRODUCTS: Diane McGarvey
emits as much greenhouse gas as a car Having worked in the industry in the
driven more than 1,800 miles. 1970s and having followed it since then, I
How to Contact Us
observed at least 15 years go by before
FIAlA RePlIes: My numbers assume that all cow pro- U.S. auto executives acknowledged their
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Scientific American Department, Scientific American, 415 Madison Ave.,
Second, to meet the demand for increased con-
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Letters may be edited for length and clarity.
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underestimates cows’ impact. Multiplication of my wscwiawm.SmcaiegntificAmerican.com/ iinn faolrl mreagtiioonns f oorf sthaele Us .rSe.p arnesde innt oatthiveers c oofu Snctireienst.ific American DY PoTTs
CAFO figures shows that assuming all animals are N
A
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SCIENTIFIC AMERICAN © 2009 SCIENTIFIC AMERICAN, INC. June 2009
50, 100 & 150 Years ago ■
Innovation and discovery as chronicled in scientific american
Space Food Zeppelin II Safe Passage
■ ■
Compiled by Daniel C. Schlenoff
JUNE 1959
scenes. Nowadays, a more or less coherent sons who earn a livelihood by collecting
SELF-REPRODUCTION—“ The construction story must be unfolded, for which reason snails for market. Snails are in high favor
of a machine capable of building itself the makers of moving pictures have been with French epicures, and immense num-
might be judged to be impossible and compelled to write plays (or at least to bers of these mollusks are eaten in Paris.
to belong to the category of perpetual- conceive them) and to have them acted be- In the winter of 1900 the consumption of
motion engines. Together with Roger Pen- fore the camera.” snails in the French capital amounted to
rose, I have approached the problem in a some 800 tons.”
radical manner, without the encumbrance WAY UP HIGH IN THE SKY—“ The illustration
of prefabricated units such as wheels and which appears below will give the reader JUNE 1859
photoelectric cells. Our idea was to design an excellent idea of the general construc-
and, if possible, to construct simple units tion of the latest Zeppelin airship ‘Zeppe- SAFE AND FORGOTTEN—“ The benefits aris-
or bricks with such properties that a self- lin II’ [also designated LZ 5], which re- ing from constructing vessels with water-
reproducing machine could be built out cently made a record flight of about 900 tight compartments were fully displayed
of them. —L. S. Penrose” miles. The airship consists of a trussed al- in the case of the iron screw-steamship,
uminium frame having tapered ends, con- Edinburgh, which plies between New
SPACE MENU—“ The problems of eating taining 17 separate gas bags filled with hy- York City and Glasgow. On the 6th of
and drinking under weightless conditions
in space, long a topic of speculation among
science-fiction writers, are now under in-
vestigation in a flying laboratory. Prelimi-
nary results indicate that space travelers
will drink from plastic squeeze bottles and
that space cooks will specialize in semi-
liquid preparations resembling baby food.
According to a report in the Journal of
Aviation Medicine, almost all the volun-
teers found that drinking from an open
container was a frustrating and exceed-
ingly messy process. Under weightless
conditions even a slowly lifted glass of wa-
ter was apt to project an amoeba-like mass
of fluid onto the face. Drinking from a
straw was hardly more satisfactory. Bub-
LIghTER-ThAN-AIR FLIghT: The Zeppelin II, 1909
bles of air remained suspended in the
weightless water, and the subjects ingested
more air than water.” drogen. The lifting power of the airship is June, when 186 miles east of St. Johns,
about 16 tons. Plans are on foot for the es- Newfoundland [350 miles north of where
JUNE 1909 tablishment of a regular airship line be- the RMS Titanic sank 53 years later], she
NE 26, 1909 WRITERS NEEDED—“ Moving pictures are tween several of the large German cities.” shterru fcokr awna ircde bpelragt ews hwileer ien s at odveends ei nfo bgy, atnhde
O. 26; JU eaxnhdi bhiatellds iinn athbeo uUt ntietne dth Sotuasteasn.d W thiteha ttehres rSiNcAuIlLt uLrAeW, a—f“t eTr hae cFarreenfcuhl eMxainmisitnear toiof nA ogf- ccoomllipsiaorntm. Beneitns,g t dwiov iodfe tdh ienseto a tw oantceer- fitilglehdt
N
N, VOL. C, raalspoid c ospmree aad m oaf rtkheids nchewan agme iuns etmhee pnut bhlaics tthues osuf bthjeec ts,n haails’ ebsyt adbelfiisnhiendg ‘stnhae illes gaasl asntai-- uthpi,r tbyu ht otuhres ,o dthuerirnsg fl woahticehd ptherei ovde sssheel rfaonr
CA taste. Spectators were once quite content mals injurious to vegetation, and therefore back to St. Johns. Had this vessel not been
MERI with a view of factory employees going to legally subject to capture and destruction built in compartments she would have
C A
NTIFI and from their work, the arrival and de- at all times and seasons. This decision has sunk to the bottom in half an hour after
CIE parture of railway trains, and similar created dismay among the numerous per- she struck.”
S
7
www.ScientificAmerican.com © 2009 SCIENTIFIC AMERICAN, INC. SCIENTIFIC AMERICAN
updates ■
Whatever happened to...?
Fuel-Cell Progress Hearty Turnovers Hurricanes Pros t a te Test Verdict
■ ■ ■
Edited by Philip Yam
■ Revving Up Fuel Cells consists of zinc oxide clusters
■ Lightning-Fast Warnings
Progress toward hydrogen- linked by an organic material;
Storms could become more intense as the world warms
powered cars depends on less one gram has the surface area
[see “Warmer Oceans, Stronger Hurricanes”; SciAm, July
expensive but greater capacity of 5,000 square meters, near-
2007]. Researchers studying 58 hurricanes found that an
fuel-cell systems [see “On the ly the size of a football field.
increase in lightning tended to precede the strongest winds
Road to Fuel-Cell Cars”; Details of the substance,
by a day. For instance, monitors tracking Hurricane Den-
SciAm, March 2005]. Re- dubbed UMCM-2, appear in
nis in 2005 recorded a surge in lightning flashes—from
searchers have taken big steps the April 1 Journal of the
600 a day to 1,500—nearly 24 hours before wind speeds
on both the cost and storage American Chemical Society.
doubled and peaked at 150 miles per hour. The correla-
challenges. A team from Que-
bec came up with a recipe that ■ New Heart Cells tion, reported online April 6 in Nature Geoscience, needs
from the Atomic Age more data before lightning can be considered a definitive
uses iron instead of expensive
predictor of storm intensity.
platinum to catalyze the elec- Aboveground nuclear testing
tricity-making reaction of in the 1950s spewed radioac-
hydrogen and oxygen. The tive carbon 14 and other iso-
key was carbon structures topes worldwide. Plants
containing microscopic pores, soaked up the compounds,
which were filled with iron to animals ate the plants, and
provide plenty of active sites humans ate both, inadver-
for chemical reactions. The tently creating an experimen-
iron-based substance, de- tal opportunity for Jonas
scribed in the April 3 Science, Frisén of the Karolinska
Institute in Stockholm and
his colleagues. They have
used the decay of atomic age
carbon 14 as a biological
marker to determine how
frequently the body replaces suggests that stimulating the ment could cause impotence
its cells [see “Cold War turnover mechanism could and incontinence. First results
Clues”; SciAm, December repair damaged hearts. from large, ongoing U.S. and
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