Geoscience Reference
In-Depth Information
the outside, where it can release heat to the exterior and into an
atmosphere or outer space.
When the plate tectonic machine has seized up, the heat, for a
while, will simply build up, causing magma to accumulate and pool
at depth underground. Then one can envisage a less active, more
patchy reprise of the heat-pipe Earth of early Precambrian times (see
Chapter 3), with magma channelled to the surface via more or less
stationary vertical conduits, to release its heat via very large shield-
like volcanoes that may, perhaps, reach the size of ancient Olympus
Mons on Mars, or some of the volcanoes on Venus (see Plate 5).
The hot, dry, baked Earth—nothing at all like the beautiful blue
planet of today—will be long-lived, for there will be something like
3 or 4 billion years yet of this lifeless existence. Then the Sun, having
finally exhausted its reserves of hydrogen, will begin to puff out into
its red giant state, out beyond the orbit of Venus. The Earth may then
simply be engulfed, or perhaps it might be expelled into outer space
by the final blowing off of the outer layers of the Sun, to drift forever
in the dark.
This is the normal fate of what, for part of its existence, would
surely have been one of the jewels of our galaxy; but it is the fate
of many planets to bloom only briefly with all the possibilities that
liquid oceans can offer. Even the other planets and moons of our own
solar system, orbiting their unremarkable yellow star, can show the
many forms and many histories that planetary oceans can have. It is
these that we turn to next.
Search WWH ::




Custom Search