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What Really Killed the Dinosaurs?by Howard Lee,
Scientifc-American | Aril !", #!$% !&'!!am ()
An e*traordinary +esselart shi and art drillin ri is bein e.uied
in the
ort o/ 0roreso, 1e*ico, to drill into (arth2s ast3 )his srin and
summer it will
attemt to reco+er a thin cylinder o/ roc4, 5 6 inches wide by
5,5!! /eet lon,
startin in the (ocene world about "! million years ao, drillin
all the way bac4 into
roc4s created and contorted by an asteroid imact, %% million
years ao, when the
dinosaurs disaeared3
Amon its many scientifc oals, ithe ro7ectmeasure new dates /or
the 8hic*ulubimact widely blamed /or wiin out the dinosaurs since
that theory was frst
roosed in $9:!3
)he new dates, usin the latest eneration o/ hih-recision roc4
datin techni.ues,
are needed because a .uiet re+olution in (arth Science has
trans/ormed our
understandin o/ mass e*tinctions (arth;s ast, includin the
end-8retaceous mass
e*tinction3
EARTHTIME
At the center o/ this re+olution is (AR)H)such lead3 )he rate
they do that is called the @decay
constant@ and is 4nown +ery recisely3
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the archer eers his arrows a l o+er the taret, he is accurate
but not recise3 the sread o/ o*yen-star+ed dead Eonescalled
@ano*ia@ is another, which itsel/ is triered by a cascade o/
bioloical
conse.uences /rom ocean acidifcation and lobal warmin3
8hanes that ta4e lace o+er timescales loner than $!,!!! years
tend to be
neutraliEed by comensatin chemical resonses in the oceans and on
land, so a
lausible dri+er o/ ocean acidifcation has to o+erload the oceans
in under about
$!,!!! years3
$,!!! years is rouhly the time it ta4es /or the world2s oceans
to mi* comletely
today, but in warmin climates it could ta4e loner3 Lare
8F# emissions o+er
centuries >li4e human emissions are mainly absorbed by the
sur/ace layer o/
oceans be/ore it has a chance to be mi*ed and diluted into the
/ar larer reser+oir
o/ the dee ocean, leadin to li/e-challenin lobal warmin and
sur/ace ocean
acidifcation3 )hese eoloically @/ast@ chanes tend to be danerous
to li/e3
http://www.pnas.org/content/106/9/3017.shorthttp://www.pnas.org/content/106/9/3017.short
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Better dates
ntil recently roc4 date uncertainties were tyically several
million years /or roc4s
more than about $!! million years old3 )hat2s more than $!!
times worse than
needed to answer these .uestions o/ coincidence and ace in mass
e*tinctions3
=ut scientists ha+e now drastically reduced those uncertainties,
achie+in date
recisions that are lus or minus about $5,!!! years /or dates in
the 8retaceous, or
about "!,!!! years /or dates in the 0ermian eriod3
As a result, o+er the last three years or so, a series o/
landmar4 aers has used
these new hih-resolution dates to nail the lin4 between se+eral
mass e*tinction
e+ents and an eic class o/ +olcanic erution called @Lare
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1e*ico >the @0ress-0ulse hyothesis@3 )he
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about hal/ a million years >which is why the
end-8retaceous e+ent was re+ised /rom
%" to %% million years ao3
)his dierence adds /uel to the debate surroundin the rincial
cause and order
o/ e+ents surroundin thismass e*tinction3
Berta Keller o/ 0rinceton ni+ersity has lon arued that the
8hic*ulub imact
occurred $!!,!!! years or more before the mass e*tinction, so
there/ore can2t ha+e
caused the mass e*tinction itsel/, which she and others
attribute the Deccan L
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the @ulse@ o/ the0ress-0ulse e*tinction hyothesis at
e*actly the same time >as /ar
as date recision allows3
=ut there2s a wrin4le3 or some years now the date o/ the
e*tinction has
been assumed to be the same as the date /or the imact
an assumtion criticiEed
as @circular reasonin@ by 0ro/essor Keller3 Within the wide date
uncertainties o/ a
/ew years ao, that assumtion seemed reasonable and ractical to
many
scientists3 =ut now, as eochronoloists allow us to Eoom-in to
the end-8retaceous
mass e*tinction in unrecedented detail, they can bein to tease
that assumtion
aart3
8learly, bein able to comare recise dates /or the imact itsel/
>rather than
distant traces o/ it, the e*tinction itsel/ >rather than the
imact as its assumed
ro*y, and the erutions, is oin to be critical3
Driing the impact
)hat2s where the new 8hic*ulub drillin ro7ect, led 7ointly by
the ni+ersity o/
)e*as and
