231
Indeed, life may have arisen
elsewhere and been transported
to Earth. Greek philosopher
Anaxagoras first suggested this idea
of “panspermia” in the 5th century
bce. Naturalist Charles Darwin briefly
turned to this idea while working
on his theory of evolution by natural
selection, troubled that the accepted
figure for Earth’s age did not give
enough time for complex organisms
to evolve. Earth is now known to
be vastly older than was believed
in Darwin’s time, so panspermia
is not needed to explain the origin
of life on the planet.
Recent discoveries show that
comets can carry many of the
basic chemical components of
life, but the exact mechanism by
which life on Earth began remains
a mystery. Solving that mystery
should give a far better idea
of how likely life is elsewhere.
Where is everyone?
One day, over lunch in Los Alamos in
1950, Italian scientist Enrico Fermi
asked a simple question: “Where are
they?” He reasoned that, even if only
a small proportion of planets play
host to intelligent life, given the
unimaginable numbers of stars
within the galaxy, one might expect
a large number of civilizations
to exist on other planets. At least
some of them may have chosen
to send messages or tried to visit
Earth themselves. Earth has been
producing electromagnetic signals
for 90 years or so, since the dawn of
radio and television broadcasting.
These modulated radio waves—
expanding and extending some 90
light-years in all directions—should
be a giveaway of a technologically
advanced society to any potential
spacefaring intelligence.
In 1959, Giuseppe Cocconi
and Philip Morrison suggested a
bandwidth to search for alien radio
messages. A year later, Frank Drake, ❯❯See also: Radio telescopes 210–11 ■ The Space Race ■ Exploring the solar system 260–67 ■
Exoplanets 288–95 ■ Shklovsky (Directory) 338 ■ Carter (Directory) 339 ■ Tarter (Directory) 339
NEW WINDOWS ON THE UNIVERSE
Computer simulations have shown
that it is theoretically possible for
simple single-cell life forms to exist
inside comets or asteroids and to
survive an impact like this with Earth.There is an immense
number of stars
in the universe.If life survives
for long enough, it may
become intelligent
enough to start looking
for life elsewhere, as
humans have done.The search for
extraterrestrial
intelligence is
a search for
ourselves.Most of these stars have
planetary systems.Life may have arisen
on many planets.