A Scientist at the Seashore (Dover Science Books)

110 Pages·2005·17.806 MB·English

by  James S. Trefil

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Copyright
Co py right 1984 by Jam es Trefi l
:1;)
All ri gh ts reserved .
Introduction • •
VII
1
1 Look at All That Water
Bihlio vra nh ir nl N fl /p
Copyright
Co pyright © 1984 by Ja mes Trefil
All ri gh ts reserved.
Introduction • •
VII
1 Look at All That Water 1
Bibliographical N ote
2 The Salt Salt Sea 11
T his D over ed ition, first pu blished in 2005, is a n unabridged , sligh tly co r
rected republicati on of th e wo rk as p ublis hed by Co ll ier Bo ok s. Macmillan 3 The Tides 23
Pu blishin g Com pa ny, New York , in 1987. The wo rk was o rigina lly publi shed
4 The Search for Planet X 37
in 1984 by C ha rles Scribn er's So ns, New Yo rk .
5 The Back of the Moon 50
0/
Library Congress Ca taloging-in-Publicauon Data 64
6 Making Waves
Trefil , James S., 1938-
7 The Surf 79
A scien tis t at the seash ore I James Trefil : illustrations by Gl ori a Walters.
98
p. em. 8 Bubbles in the Foam
O riginally publi shed : N ew York : Scribner, cl984.
112
9 The Shape of the Wave
Includ es index .
ISB N 0-486-44564-X (p bk .)
128
10 Queen Anne's Pudding
I. Physics. 2. Beach es. T. Title.
11 Of Beaches and Baseballs 142
QC?8 .T67 2005
530-- dc22
158
12 Castles in the Sand
The science of physics, in addition to giving us the ability to describe
and predict the behavior of all objects from galaxies to electrons, also
provides us with a unique view of the world. ' T he key factor in the
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j.' ...
The science of physics, in addition to giving us the ability to describe
and predict the behavior of all objects from galaxies to electrons, also
provides us with a unique view of the world. ' T he key factor in the
physicist's outlook is the concept of natural law. When the period of
turmoil that characterizes the birth of a new science is over, the physicist
expects to find a set of basic regularities that hold true in the area being
studied. For example, in 1687 Isaac Newton summarized the principles
of mechanics (the area of science concerned with the motion of material
bodies) in his three laws of motion . Everything that had to do with
motion , from the orbits of planets to the fall of an apple, was contained
in these three simple laws. During the nineteenth century, two more
areas of nature were explained in corresponding fashion: heat in (th ree
laws of thermodynamics) and electricity and magnetism (in four laws
called the Maxwell equations). In this century gravitation (one general
•
principle of relativity) and quantum mechanics (four or five basic pos
tulates, depending on which side you take in some ongoing debates)
have been added to the list.
The lesson to learn from these developments is this: If everything
I NT ROD C T ION I ix
U
viii I A SCI E NTIS TAT THE SEA S H R E
0
. ' db this example of a non sequitur, particularly
I
I
a~mit .wa~~~n~~~n ~n St~nf~rd
available to our senses, this web must become more and more con
that I the shore of Lake Lagunita on the
f
I
,
stricted as we follow it, until finally every strand ends at one of the great smce I read It w II e si I spent my lunch breaks reading and eruoying
physical principles mentioned above. ;' campus,. where regu ar y rsonal feelings aside, I have never been
Btautd~
From this view of nature an important conclusion can be drawn. If the sunlight on watder. omething makes it less beautiful. An
t how un ers n s h b
109
bl
every phenomenon we encounter ultimately leads us to one of the
a e see. f h behavior of light doesn't detract from t e eauty
0
understa~dm~ ~
Anything
general laws, then it makes no difference where we start. can .t r does understanding the role of stress and
0
~ r~
serve as the starting point for an inquiry into the workings of the physical of B?ttlcelh painting, cathedral make the experience of walking
strain the structure o. mind deeper understanding makes
world. You don 't have to start in a laboratory because, in a very real 10
compelh~g. ~f
into one any.less To;y the most pleasant of natural
sense, the entire world is a physics laboratory. So important is this truth
o~e
experience ncher. A beac -:per aAPs ti t walking on the sand sees
that the present book is entirely dedicated to the exploration of one site,
. exception scien IS
environments-IS no . I d s The fact that he knows
a beach, for clues to the ultimate workings of the universe.
thatfanho~~:s~es ~~~s
the same things there. not diminish his powers
We shall see that the ebb and flow of the tide is connected with the
more about some portion w a . .
0
fact that no one on the surface of the earth can ever see the back side
. . th ality of his enjoyment.
i~'t
of appreciation nor e to walk along your favorite beach
of the moon, and related as well to the search for new planets in the
~o~
With this assurance, mVI e f h rience by seeing some
solar system-a search which may not be over even today. Waves and
with me, deepening your appreciatIon t e expe
0
surf are related to new technologies for communication and to research
of it through my eyes.
into the past climates of the earth. Something as ephemeral and in
JAMES TREFIL
consequential as a bubble in the foam leads us to consider the forces
Charlottesville, Virginia
that hold the nucleus of the atom together. Even an ordinary sailboat
has its tale to tell and its lessons to teach . At every turn, we find new
corroboration for the beautiful and elegant concept of natural law.
. , t h .ence by seeing some
with me, deepening your appreciation t e expen
Before we step down to the beach, let me sav ~L 0
fpw.wnrrl< ...
;I
mA"O
.' . ~ __ ._._._~ .u ,,"vv lculliulugies ror communication and to research
of it through my eyes.
into the past climates of the earth. Something as ephemeral and in
JAMES TREFIL
consequential as a bubble in the foam leads us to consider the forces
Charlottesville, Virginia
that hold the nucleus of the atom together. Even an ordinary sailboat
has its tale to tell and its lessons to teach. At every turn, we find new
corroboration for the beautiful and elegant concept of natural law.
Before we step down to the beach, let me say a few words more about
the physicist's viewpoint you will find in this book. You will perhaps
be struck first by the fact that all the topics I choose to discuss deal with
inanimate objects-waves, sand, stones, and so on. This isn't because
as a
I don't see and enjoy the wildlife along the beach. I do. But
physicist,
I have nothing unusual to say about it. Because I am not
trained in zoology or botany, I simply can't see the web to which sand
crabs and gulls are connected, nor have I anything more than a layman's
which
knowledge of the principles made them the way they are. I have,
therefore, chosen to confine myself to subjects where my own special
training is of use. This is but to follow Emerson's old dictum, "Tell us
what you know."
The second point has to do with an attitude I sometimes encounter
in people with whom I've discussed scientific ideas. They argue that
understanding how something works somehow diminishes our aDDTe-
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Little drops of water
Little grains of sand
Make the might y ocean
And the pleasant land
Little drops of water
Little grains of sand
Make the might y ocean
And the pleasant land
- JULIA C ARNEY ,
" Little Things"
Stand at the edge of your favorite beach and look out. You are seeing
one of the most unusual sights our universe has to offer: large amo un ts
of liquid water. Furthermore, you are looking at watcr that has existed
in a form not too different from its present state for billi on s of years .
This perception of the oceans of ea rth as a unique phenomenon is
fairl y n ew. Those who read science fi ction will have viv id memories of
the "canals of Ma rs" and the "swam ps of Venus." Less than a quarte r
century ago the best scien tifi c guess as to the nature of our planetary
the nresence ofla rge amou nts of water. On Mars,
n p;nhhm c mnn, pcl
nYP Cl
2 I
13
A SCIENTIST AT TH E S E A S H O R E
L O OK AT ALL THAT WATER
sheets. O n Ve n us, th e cl oud cover prevented us from seeing the surface sing~e
We kn ow that the plan ets and the su n were formed in a process
mA~ ence
but it didn 't prevent us from im agining the planet as an overgrown
in wh ich a cl oud of rotating gas slowly co n tracted under the
ve rsio n of the Florida Eve rglades. In both cases, our view.ef neighboring
of its own gravitation al attraction . As might be expected from thi s PIC
b~
plan ets was sh aped by th e expectati on that water, so plentiful on th e
ture , th e largest body in the solar syste m must at th e center, where
earth , must be plentiful eve ryw here else in th e solar syste m.
the greatest amount of gas coll ected . This body IS the star we call the
Th e planeta ry explo ratio n program h as changed man y things about
su n . The h eat generated by the collapsing gas eventually becam.e so
the way we view different environ me nts in the so lar syste m. The new
great at the su n's core that the nucl ear fusion reacti on was Igmted .
c?ncept of "spacesh ip earth " has made revoluti onary changes in o ur
H ydrogen nucl ei were forc ed together to form helium , and th e energy
t~mpo~a.nly
view of the earth , and bro ught us closer to a sense of th e u ni q ue privilege
released in this rea ction , strea m in g o utward from the core,
of being ea rth lings.
stab ilized the su n aga inst further collapse. This " te m pora ry stab iliza
Following the Copernican revolution , man has learn ed to view the
tion has lasted about 4 . 5 billion yea rs so far, and will go on for about
ea rth as a plane t -on e of man y circling the su n . Sir Isaac Newto n
5.5 billi on years into the future, when the sun will have burn ed up all
developed a picture of the universe in which the earth was shaped and
of th e fu el that was gathered together in the initial contractr on . At th at
gove rned by the sam e laws of ph ysi cs that prevail everywhe re. It thu s
point the su n will die. . .
com es as something of a su rprise for us to realize that alth ough the
O uts ide of the sun, another proc ess was occurnng m the solar sys-
same laws operate on earth as elsewhere, those laws have produced a
tem-a process that we still do not understand in great detail. Clumps
plan et which is radically different from its neighbors. N owh ere is thi s
of gas that had been rotating too fa st to fall into the proto-sun and that
difference more glaring th an in th e existence of oceans.
were therefore left in orbit began to combine to form aggre gates th rou gh
Th e Viking missions to M a rs sent back photographs of a n a rid, lifeless
th e same grav itati on al m echanism that had formed the su n . At d istances
surface; the polar caps turn ed ou t to be frozen carbon di oxide (d ry ice)
from the su n that n ow characteri ze the orb its of the plan ets, such clumps
~howed
T ests n?thing that cou ld n' t be expla ined on th e basi s of ord ina ry
of gas began to coll ect. As far as we can tell , this process was rand om .
c hem ical rea ctions-if there is water th ere, it must be buri ed deep
Somew here in th e thin rotatin g cloud sma ll cl umps of mat erial ha ppened
a
.. ..... .J ~~ l 1" - - 1 1 .. . - - -- -- .. .... . _ .. ..." ....£ • ...,....... .a" "y" JJ Q V\,.. pJ VU U C CU tem-a process tnat we ' ti ll lft, lIUl UIlU<: I ~ldll\.J II I 5 "'0 ' ~~'u .. . ~ .~ .. . t'0
plan et wh ich is rad ically different from its neighbors. Nowhe re is thi s
of gas th at had been rotating too fa st to fall into th e proto-sun and th at
differen ce more glaring th an in the existe nce of oceans .
were therefore left in orbit began to combin e to form aggregates through
Th e V iking missi ons to Ma rs sen t back photographs of an arid , lifeless
th e same grav itation al m ech anism that had formed th e su n. At distances
su rfa ce; the polar caps turn ed ou t to be frozen carbon di oxide (d ry ice)
from the su n that n ow characteri ze the orb its of the plan ets, such clumps
~ h owe d
T ests n?thing that co uld n' t be explain ed on the basis of ordinary
of gas began to collect. As far as we ca n tell , this process was rand om.
;
,
i
chem ica l rea ctlons:-if there is wa te r there, it must be buri ed deep
So mewhe re in the thin ro ta ting cloud sma ll cl umps of mat eri al ha ppened
I
underground . Similarl y, Ve n us, with its surface temperature of 800
0 to fi nd th em sel ves close together. T he en hanced gravitational anracnon
Fa h ren hei t, is n ow known to be much too hot to sus ta in liquid wate r.
of this co llection att rac ted still more mat erial to th e spot. which in tu rn
O f all of th e plan ets in our sola r syste m, on ly the ea rth has ocea ns.
made the gravita tiona l force even greate r. It's not hard to see th at the
W he n th e human race begins to m ove awa y from th e surface of the
process wo uld event ua lly result in most of the mass in a give n a rea being
earth an d th e first perm an ent extrate rrestrial habitations a re built in the
co nce nt rated in o ne spot.
next cen tury: the age-old balm of a quiet walk along th e seas ho re may It used to be thought that thi s was how the earth was form ed: a
,i
become a thmg of the past for our spacefaring descendants. random even t initiated a collapse until all of the available m atter had
II So the oceans of earth present us with a puzzle. Given that the sam e been swept into a single body. In th e last decade, howev:r , thi s picture
,
,
laws of nature operate everywhere in the solar system, wh at is so special h as been refined. The best available theories now descnbe th e process
'I
about our planet that on ly we are pri vileged to ha ve large bodi es of of plan et formation as having two steps. First, the gravi.tati on al co llapse
,!
w~ter
IIq.Uld on our planetary surface? What are the uniqu e ch aracter we've just described took place, fanning sm all, asteroid-like bodies known
~ass
ISti CS wh ich make the earth so different from the other planets eve n as plan etesimals -some as large as 1/ 500th the of the ea rth. T he
lar~er
though the sam e laws ope ra te here as elsewhe re? '
planetesimals then began to collide and combin e to form the
~rowtng
To r: sol ve this question , we h ave to deal with two sepa ra te issu es: bodies of th e planets. The rain of bodi es o n the surface of the
H ow did ~~m ';M ", .~l..
th F F:" t h _ 1 . . r- . . _ • • • r 1 • ~ L .1.- •• ~~ l.. .......... ... "" ... Dl&>_
/ 5
L OOK AT A LL T H A T WA T ER
4 /
A SCIENTIST AT THE SEASH OR E
volatiles in this way is called degassing. Over a relatively short time
p~ocess started to occur. When a meteor h i t s ' .
100 million years or so enough volatile m ateri al had been released in
sticks and some is scattered b k i anyting, some matenal
ac into space by the O f '
j this way to form the oceans and to give the earth an atmosphere . It
scattere material some i . e Impact. this
d d ' s moving lCast enough t b k i or~it
wasn't an atmosphere like our own; there was almost no free oxygen,
an some is eventually pulled back to the l o g o ac into
for one thing. But it was a collection of gases wh ich were h eld at the
of the material the more lik I it i p anet. The lower the den sity
. ' le y I IS to escap Th . h
planetary surface by gravity and wh ich therefore deserves the title of an
o ItS formation the earth call t d h e. us, In t e early stages
f ' ec e eavy material Ie . I' h
sue as silicon and water) still' bi ' avmg ig ter stuff atmosphere.
( h
A th h m or It around the sun Early in this history, perhaps almost from the beginning, the tem-
s. e eart began to approach dits '~resent . .
perature of the earth fell below 2 120 Fahrenheit and the water condensed
growing gravitational attraction h d Size, however, the ever-
a~
ma
into oceans as we know them today. This is not to say that our present
escape. By this time most of th e I . er and harder for debris to
. ' e matenal m the ' . ity f h
oceans formed 4.5 billi on years ago far from it. It sim ply implies that
or It consisted of debris of . II viciru t e earth 's
0
b previous co ections and th
C the large amounts of water we associate with an ocean were on the
pose argely of lighter eleme ts Th h was ererore com-
d I
. ki n . e eart swept thr h thi
scene within a few hundred million years of th e earth 's creation. As we
pre 109 up mass the way the windsh ield of . oug . IS material ,
shall see in the next ch apter, the present ocea n structu re is fairly new,
on a su m mer afternoon Th T a movmg car picks up Insects
the Atlan tic Ocean being only 165 million years old.
beach, as well as the water the t Sl Icon that makes up the sand on the
a;;~~~:P~he oc ~an ,
0:
The weigh t of geological evidence po ints to another amazing fact
earth during this last phase were added to the
about the early oceans. The amount of water contain ed with in the
you see, therefore, has probabl b . ' ach bit of sand or water that
Its history. y een m space more than once during oceans has not changed appreciably since they were formed. T he mass
24
of water in the oceans now (about 10 gm) is ro ughly the same as the
Th e form ati on of th e ea rt h f
mass of water that was co nta ined in the crust of the earth wh en the
fro m th e bulk of the . . I rom pla ne te sima ls a nd th e s un
I d o rigma gas clo ud too k I '
degassing started. F urtherm ore , we can estimate th e rate at whi ch water
Y a n requ ired a few hund d '11' pace sim u lta neo us -
r~h ~I
is being lost today. The water m olecule is too heavy to escape the ea rth's
W hen the ea rt h wa s fo r m ing .lO n yea r.s t o be compl et ed .
o"v'V&'~u , .t" ~ u" -
ed. It was not a , e u si on rea cti on In th e s u n ig ni t- lilt W t l!!>' " Vi 'u " ' - . 11__
smoot h ¥ .. _ _ .. _ _
h
~ ~ . ·-' t3 cl_ .....~.t: h '""'LI1 ·1 about the early oceans. The amou n t of water contained within the
n r r\r p 40: C .......
you see, t erefore , has probabl been i ' lIlar
J Q.\ ..... W dlC I
V'- V I
Its history . y een space more than once during oceans h as not changed appreciably since they were formed . T he mass
lo
24
of water in the oceans now (about 10 gm ) is rou ghly the same as the
Th e form at ion of th e ea rt h f
mass of water that was co nta ined in the crust of the earth when the
from th e b u lk o f th e . . I rom pl an etesim al s a nd t he s un
I o r igina ga s clo ud t k I '
degassing started . F urthermore, we can estimate the rate at whi ch water
y a n d required a few hund d ' II' p ace sim u lt a ne o us -
0 0
r~h ~I t ~
is being lost today. The water m olecul e is too heavy to escape the earth's
W he n the ea r t h was fo r m ing .lO n yea r.s be com pl et ed.
p ro ~e s se a ~~lO n
gravitational pull easily , but water molecul es in the air are occasio nally
ed. It was not a sm o o t h reactl.on th e s u n igni t
10
ca r engine o n a cold . ' ca n be likened to st a rtin g a
dissociated (b roken up into the constituen t hydrogen and oxygen). T he
:o r~ lOg.
ba ck fir ed fo r a while Th e s u n st u tte red , b a lked a nd
s te lla r~vo' ~ he hydrogen freed in this way is light enough to move off into space, which
l
Tauri st age in SIu tuatlOnE a shtro no me r s de sc ribe as T
is why there is so littl e free h ydrogen in the earth's atmosphere. The
Ion . ac Oa rin g f h
st ro ng st rea ms o f pa rt icles r .hi u p t e su n se n t
0 net effect of h ydrogen loss, then , is to decrease the amount of water
rem a in in g gase s o ut of t h .us in g o ut. Th ese pa r tic les swep t th e
vapor in the atmosphere- water vapor wh ich is replaced by evapo ration
it s present st at e H a d th e .a rt h so lar system, leavin g it in mu ch
. t h . e eart been form ed .th
from the ocean s.
a m ? sp ere presen t . it wo u ld have be WI , a rea dym ad e
bhl o w~ ~ t About 5 X 101 1 grn of water are lost thi s way each year. T h is co r-
leavin g the ea rly ea r t h a s a rocky ba ll e n o tf thi s time,
responds to a cube 100 yards to a side- abo ut the volu me of a small
o n Its s u rface. Wit neith er ai r nor wate r
lake . All the water lost to space since the beginn in g of the earth amounts
But if all of the water in the atmo~h x
to abo u t 2 10 gm- less than 0.2 percent of the water in the ocean s,
solar system by the su n's fl ere had been blown out of the 2 1
~re-IuP,. w
In fact , all of the wate r lost to space since the beginning corresponds
from ? The answer parado ere co uld the oceans have come
i '
. id , Xlca as It may seem . th t th
to a square of ocean abo u t eigh t hundred miles on a side . T h is means
,
InSI e the earth . The out I f h , IS a ey came from
that most of the water you see when yo u stand on the beach is, in fact,
including water wh ich herdabyer t e planet was rich in light materials
0 .\" ~ ;~ 'o r;r.r
,. ' cc .. . n ,h pn th p p:lrth
b a een swe.p+thmu~·l.T~ -h ~ e~, wo ~l d a ~r-' 1 _ . ' _ J L _ _
ulent place, with was
vo lc a n o e s 'I nri
: _
p ... c
6 /
A SCIENTIST AT TH E SEASHORE
/ 7
LOOK AT ALL THAT WATER
fI '
chapter I, shall discuss the process by which n ew 0
by matenal moving up to thc surface h' cean oor IS created Having found the origins of the ocean in the processes that form ed
;'a~~rs ~~i~~e ol~ f1o~~sidde,
the earth, we ca n turn to the seco nd (a nd more difficult) problem we
upwelling material contains some This
oceans, balances the loss to ' . ' w. en e to the posed earlier. Given that there was enough water to form the oceans
s~~ce,
'1
to the oceans " , GeologIsts call thIS material added
early in the earth's history , how is it that the water is still here now,
e water (W hen I ientifi
, [uven:
~'
velous as this I wee see a scienti c term as mar-
some four billion years later? Presumably the scheme outlined above,
h " . eep or my own field, elem entary artie] hvsi
n "
in which a planet degasses after its formation , could have happened on
w ose contnbutlOllS include terms k" d P , e p ySICS,
~uar
"strangeness" and "co l " F I e an mIsnomers like
any of our neighbors in the solar system , including th e moon. Wh y,
to Quarks ,)* From Atoms
or. or more on this, see m y book
then, has the earth alone retained its oceans?
The case of the moon is eas y to understand. Because of its light mass,
In an y case, the balance betw
atoms in the moon 's earl y atmosphere had an easy time escaping into
space. Long ago they slipped off, leaving the surface exposed to vacuum
sur ace must c roughtl
I
time It d t h Y con stant ove r long periods of
as it is today, The case of the planets is a little more com plicated, so
~es ~~ '
I form ' 0 . owever, mean that all that water must be in liquid
i
that to understand the present state of the earth we must turn to the
o~ea~;I:~s I:c~~~ a~preclifabhle
the ;es, anI, portion of the water now in
remarkable concept of the "continuously habitable zone " (C H Z) intro
p g aci ers. t ere IS a fixed t f
III
1978.
on the surface, then it follows that arnoun water duced by astrophysicist Michael Hart in
J . 0
of the oceans Thu s h ' g aciers can grow only at the expense
But first we have to realize that during the lifetim e of the earth a
Eur . . " w en Ice covered most of North America and
number of major changes have taken place in the en vironment, an y
ope eighteen thousand yea rs ago th e I I
th ' '- ocean eve s were lowe th
Y one of which would be potentiall y disastrous for the continued existen ce
If
d e a re now . Large portions of the No rth Sea and the B S r an
I
d
ryan , and Britain was attach ed to ' I a IC . ea were of the ocean. To begin with , the luminosity of the su n has increased
of the United States was a hu d d rules ;ndhEurope. The ea st coast
by about twenty-five percent between the time the ea rth was formed
and what is curren I n re rrn es art e r east than it is now
and the present. Had this happened with out any compensating changes
:!n .~\art
anima Is of th e ocea n floor was populated bv land
( i n r l " rl ;nn
in ih~t' atrnosnhere. th e oceans would have boiled awav lone- a20 . Sim-
at m e oceans Th hen I . ---. expense
~ o' ~" ~ ' UJ a, nu nrst we nave to realize mat aunng the ntenrn e ot the earth a
"It:
Eur . . us, w en Ice covered most of N o rth America and
number of major changes have taken place in the environment, an y
ago
ope eigh teen thousand years the I I
they are now L a r ' , ocean eve s were lower than
one of which would be potentially disastrous for the continued existence
If
d I , ge portions of the North Sea and the B S
ry and, and Britain was attached to ' I d a IC. ea were of the ocean. To begin with, the luminosity of the sun has increased
m~lll;n
States was
of the United a hund d hEurope. The east coa st
by about twenty-five percent between the time the earth was formed
and what is current] re rru es art e r east than it is now,
and the present. Had this happened with out any compensating changes
IT;al~rt
was
animals (incl ud ing of th e ocea n floor populated by land
in the atmosphere , the oceans would have boiled awa y long ago. Sim
ilarly, about two billion years ago oxygen produced b y photosynthesi s
sim ilar coastlines
In a vein , th e present of th ld
I
I
are becau se so m e of th e water su is ' e .wo r are wh ere they in algae in the earth 's oceans started to accumulate in th e atmosphere.
,I
mainl y on Antarcti ca Should th pp Y tied th e polar Ice caps,
I t III The oxygen destroyed several gases that were present in th e atmosphere
I
ocea~ Ps
flowed into the basins the Ice Ct me t so that all of the water
by reacting chemically with them. The m ost important of these were
~f
hundred fcet and flo od most the ;ea level would increase by several
ammonia and methane. Both of these compounds contributed to the
But in a e ow- ylllg coastal a reas of the world,
fewn~l~~~~~~h e greenhouse effect-they were part of the atmospheric "bla n ket" that
not a ·fact that your favorite beach is where it is and
kept the ea rth warm. Removing them was like tearing holes in that
wat~~1 s~: o~t ~~ t~e
the ea rth's total sea (or inland) is th e result of way
blanket; heat started streaming out and the earth cooled off rapidly
PP Y
ocean and the solid in I . ddlvld ed between the liquid the
III
almost catastrophically, in fact. Had the cooling been just a little more
g aCler an ICe cap.
violent and the energy coming in from the su n just a little less strong,
the earth would have fro zen solid as soon as a sign ific an t amount of
oxygen had accumulated in the atmosphere.
What Hart found was that there is a very narrow band around the
su n- a band which he called the CHZ-in which it is possible for a
8 / /9
A S CIENTIST AT THE S EASHORE LOOK AT A L L T HAT WATER
to the point where the water could condense. N ew gases added to the been form ed to sh ield th e su rface of the ea rth from the sun's ultra vi olet
I
I atmosphere sim ply stayed there , increasing the blanket effect and raising radiati on , and life- if it developed at all co u ld never have emerged
I
: I
the surface temperature sti ll high er. M ars, on the other hand;"presents from the sea .
,
the opposite picture. Because of its sm all mass and great distance from So th e m ere fact that we can stand on a beach and look out at the
I
the su n, whatever liquid water it once may have had has long since sea today, som e 4.5 billi on years after th e formation of th e earth, tells
either escaped or froz en , leaving the arid ball we see today. us that th e earth is a uni qu e place. It is unique not o n ly in relation to
The existence of the CHZ, then , tell s us where a planet must be our own sola r sys tcm but in relati on to the en ti re M il ky Way galaxy.
placed relative to its su n in order for it to keep liquid water on its surface It is possible for yo u to vis it th e beach o n ly because you live o n a pl ane t
In
for th e billions of years necessa ry for th e evolution of life. our solar whi ch is n eith er too large no r too sm all, circl ing at just th e right distan ce
system, the CHZ extends from a radiu s one percent larger than that of from its sta r, whi ch is also neithe r too large n or too smal l. And all of
In
the ea rth's orbit to a radius fi ve percent sm alle r. other words, had these co n ditions h ad to be met before the planet co uld produ ce a bei ng
the random process leading to the formation of the earth begun one capabl e of thinking about eve ryth ing im plied by stand ing on a
percent farther away or fi ve percent closer to the su n than it actuall y beach.
did , n o higher life form s would ever have devel oped on the planet at
all, and th e earth tod ay would either resemble Venus-the victim of a Hart' s discovery of th e C H Z is typical of a major (a nd unremarked )
runaway greenhouse effec t- or have been frozen solid for the past two trend in recent scien ti fic research. Wh en the questi on of extraterrestria l
193 0s,
billion yea rs. This is wha t I meant earli er when I referred to the ocean s intelligence (ETI) first became sc ienti fica lly respectable in the late
of the ea rth as unique . relativel y little was known abo ut the evolu tion of the solar system or
The same sort of reasoning that led to these rath er stringen t limi ts the ea rly ea rth . It was assumed th at since the sa me laws of nature ope rate
on whe re a planet can be located and still possess oceans can al so be everywh ere in the uni verse, th e ea rth and its environs m ust be rath er
appli ed to the properti es of the ea rth and the su n themselves. For typical of what we wo u ld fi nd if we co u ld vi sit othe r parts of th e ga laxy.
nt
exarnnle . we re the m ass rlf th e su n less rhan pj l1htv PP pnt nf Thi ~ 1 ~ nnp "'(~~ <:(ln u .J1"1\l th(-.. nrr-"l..'l 1tnnt ;nn t hr.' r-..v il,.'f-pnf" · F"l f I"\n
H ; .,J.PT'
runaway greenhouse errect-- or have been irozen d-thtoTr thnePTpar st two trend in recent scie ntihc research . W he n the qu esti on of extrate rrestria l
SOlJl
19305,
billion yea rs . Thi s is wha t I meant ea rl ier when I referrcd to the ocean s intelligence (ETI) first became scienti fica lly respectable in the late
of the earth as unique . relatively little was kn own abo ut th e evolu tio n of the so la r system or
Th e sa me sort of reasoning that led to these rath er stringen t limits the earl y earth. It was assum ed that since th e sam e laws of nature operate
on where a planet can be located and still possess ocean s can also be everywhere in the uni verse, the earth and its enviro ns must be rath er
appli ed to the properti es of the earth and the su n themselves. For typical of what we wo u ld fi nd if we co u ld vis it o the r parts of the galaxy.
example , we re the m ass of the su n less than eighty-three percent of This is o ne reason why the pres u mp tion of th e existence of water o n
:
,
I
what it is, any planet wo u ld freeze when oxygen accumulated in its M ars and Ven us was so widesp read. T his idea, called the assu m ption
I
I
atm osph ere; there sim ply wo uldn' t be eno ugh h eat com in g in to co un of m ed iocri ty, led to the well-pu blic ized con clusions th at th ere m ust
teract th e formati on of glac ie rs . O n th e othe r hand , if th e ma ss of the be m an y fo rms of intelli gen t life in the un ive rse , with the h uman race
su n h ad been twen ty percent larger than it is, it wo u ld have burn ed up bein g a very juni or m ember of the galactic club.
all of its nuclear fuel before a billi on years had elapsed . Consequently, But the last twen ty yea rs h ave see n a n eno rmo us expa nsio n of our
only sta rs close in m ass to the su n- wh at astronomers call G stars understandin g about th e ea rth and th e life upo n it, and how both came
have a CHZ and sufficient lifetim e so that planets could have ocean s into existen ce. The con cept of the C HZ is one exampl e of this n ew
like our own. Large sta rs have a large CH Z, but live for relatively short kind of und erstanding. It is ty pical of muc h of our n ew kn owledge in
times. Small stars h ave n o CHZ, bu t have long lifetim es. For liquid showing tha t alth oug h the laws whi ch opera te on the ea rth a rc the sa me
water to remain on a plan et's surface for several billi on yea rs, then , as they a re everywhe re in the uni verse , the co nditio ns u nde r wh ic h
requires a delicate balan ce between longevity and energy output in a those laws ope rate a re not. T he ea rth, because of its size, its posi ti o n ,
plan et's star.
and the kind of star aro und wh ich it circles m eets a spec ial and exacting
Simil arly, if the ea rth h ad been ten percent more massi ve than it is, set of crite ria . It is u nu sual beca u se it is one of th e ve ry few places in
the m aterial em itted in the dega ssin g process would h ave contained
the galaxy whe re oceans can exist.
•