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WHY
PLANET EARTH
IS
UNIQUE
by
John Ross Schroeder
What makes the earth so special in our solar system? Why is life here unique?
O
UR GOOD
green earth
sits rather near t he far
edge of a vast galaxy
we call the Milky Way. And
our sun is just a small to
average star m the Milky
Way.
Planet earth is one of nine
known to revolve around the
sun. Yet the earth is the on ly
planet in ou r solar sys t em
blessed with organic li fe. Why
don't the ot her planets suppor t
living organisms?
More has been learned about
our siste r planets in t he last
decade than in the previous two
millennia. Our era has been
termed " The Golde n Age of
Astronomy." Ultramodern space
technology has permitted this gen–
eration to probe our solar system
in a way that our forebears never
dreamed of. Unmanned spacecraft
have actual ly examined the sur–
faces of Venus, Mars, J upi ter and
Saturo . Meo from earth have
actually walked on the moon.
Atmospheric physicist Garry
Hunt of University College, Lon–
don, finds that the study of the
other planets inevitably turns his
thoughts back to our earth. lndeed
there is much to be learned about
the earth itself from the study of
our planetary system.
I f only learned meo knew the
March 1983
vital significance of the vast
amounts of knowledge they are
gathering from the heavens. The
spiritual implications are enor–
mous. Locked up in this new
knowledge is tbe very reason for
man's existence in the universe.
But back, now, to the earth.
Man is of the earth, earthy. So
let's start with sorne essential
phys–
ica/
knowledge about the planets.
Lessons from Venus
Since Venus is the most visible of
all the planets to the human eye, we
will begin our brief planetary
excursion with the "evening star."
Venus gets as close as 25 million
miles from the earth. Nearer to the
sun tban the earth, Venus has been
called the earth's twin because it is
abou t the same in size and mass.
The similarity ends there.
lf somehow you could travel to
Venus, three things would happen
if you dared step outside your
spacecraft. Simultaneously you
would be poisoned, boiled and
squasbed. The atmosphere is posi–
tively hostile to human life, con–
taining an enormous percentage of
carbon dioxide and a fair portion
of sulphuric acid. Russian space
probes reveal that this planet's
surface temperature is in excess of
900°F. It's hard to imagine any–
thing quite that hot.
And what about walking on
Venus? American astronauts were
able to walk on the surfac.e of the
moon with the aid of sorne highly
sophisticated space· suits. But so
dense is the Venusian atmosphere
that walking on Venus would be
like trying to take a stroll at the
bottom of the deepest part of the
ocean.
Contrast the earth's ideal tem–
perature and atmospheric condi–
tions. One could call tbe earth a
peculiar phenomenon in the solar
system. Unlike Venus it has far less
carbon dioxide and 20 percent life–
supporting oxygen instead. Venus
has no measurable oxygen and con–
sequently no life forms. There are
many elements in our atmosphere
that fit the exact requirements for
living organisms. Venus is acidic
and acid is a powerful destroyer of
proteins-tbe very stuff of which
life, as we know it, is made. In
contrast the mild basicity of the
ear th is ideally conducive for the
existence of life.
What would we do without
water? Fortunately the earth has
been blessed with a superabun–
dance of water covering about three
quarters of its surface. There is
almost no water vapor in the atmo–
sphere of Venus. According to Lin–
coln Barnett, " In the universe as a
whole, liquid water of any k:ind–
sweet or salt- is an exotic rarity"
("The Miracle of the Sea,"
Lije
magazine).
Scientists and astronomers have
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