The End of Earthly Oceans - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 195

below, but in any case the world, with us, might really be changing
rather more fundamentally than the brief ecological wrecking spree
we described in Chapter 7. Have we, perhaps, brought on a step change
that will affect both land and ocean forever?
Breaking the Rules
The Earth is, in many ways, controlled by the film of life at its surface
(as we saw in Chapter 6). Without that film, and the way it helps to
regulate element cycles and climate, it is an open question as to
whether our planet would have retained its oceans for over 4 billion
years.
We know that those long-lived oceans are currently undergoing
something of an ecological crisis that may, in a few brief centuries,
come to rank with those of the great perturbations of the Earth's geo-
logical past. If that projected crisis takes hold, with rapid ocean warm-
ing, acidification, and oxygen deprivation, then the life of the oceans
will change too, as ecosystems reassemble themselves within a mass
extinction event.
At the moment all this seems more likely than not, given the trajec-
tory and momentum of global change today. At their simplest, the
man-made changes have a good deal in common with those triggered
in the past by great volcanic outbursts or by rare, cataclysmic meteor-
ite impacts—those that we now place at the boundaries between the
Permian and Triassic periods, for instance, or between the Cretaceous
and the Tertiary.
What comes after? After the great convulsions of the past, the great
stabilizing processes of our planet swung into action: the removal of
excess carbon dioxide from the atmosphere by its conversion, ulti-
mately, into limestone rock and buried hydrocarbons; or the neu-
tralization of other toxins (fluorine, sulphuric acid) by reaction with
rocks or water. This kind of self-cleaning we know can take a few