Geoscience Reference
In-Depth Information
This means that deep oceans can exist beneath layers of ice on Earth
and (see Chapter 9) on other planetary bodies.
Imagine for a moment if the converse were true: oceans would fill
with ice from the bottom up, and thick masses of ice would likely
therefore fill most ocean basins to press down on the sea floor. Such
ice would be screened from the Sun's warmth by the water above: it
might melt very slowly from the bottom up, by geothermal heat, the
liquid produced then trying to escape upwards through the massive
bulk of ice. Perhaps life could exist in such circumstances—but there
would be little chance of the likes of swarms of fish or coral reefs.
Such a world would seem to be fit only for the toughest of microbes,
not for the extraordinary diversity of complex life that we have
beneath the waters on Earth.
Can other liquids take the place of water as crucible of and shelter
for life? There are worlds in outer space (see Chapter 9) with lakes and
seas of substances such as methane and ethane. These are rich in car-
bon (and likely there are some complex carbon compounds there
too). Simple hydrocarbons can certainly act as solvents, as anyone
who has worked in a chemical factory knows. But whether, on some
other world, they can by themselves create a kind of life, is an open
question, the answer to which currently seems to be 'probably not'.
To have life, it seems that long-lived bodies of liquid water—oceans of
one form or another—are necessary. And, for that, one needs the
right kind of planet, at the right kind of distance from its star, to form
out of the whirling clouds of interstellar gas and dust.
Birth of a Solar System
Star systems form in the clouds of gas and mineral dust—and of water
too, as vapour or as ice particles—that drift through interstellar space.
To make a star, a portion of the cloud needs to separate off, then col-
lapse under its own weight. This might happen spontaneously, being
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