Life of the Oceans - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 162

estimated age of the universe at 13.8 billion years. In that time, many
terrestrial planets with water will have emerged, and some of these
fall in the 'Goldilocks' zones of those stars they orbit. It seems that,
with the right chemistry, life might arise on these planets quite quickly
from some precursor proto-self-organizing substance. If Earth can be
used as a guide, once life gets hold it can spread rapidly across the
surface of such planets.
There may be, and may have been, many such worlds with life in
the universe. Most of these will be bacterial, and most will need to
possess large, long-lasting bodies of liquid water that we may call
oceans. Then—even with billions of years of time and relative envi-
ronmental stability—the leap of complexity to form eukaryotic
organisms may never occur, for we don't know how it occurred on
Earth. A few worlds may have made this giant leap, invented sex (or
some equivalent), and produced planets with sponge-like organisms
to filter-clean their seas as a precedent to the evolution of more com-
plex life. Here and there, and likely very rarely, a few planets may have
undergone their own 'Cambrian explosions'. Would these rarest of
planets have ever produced a Darwin to contemplate the origin of
their own kind? We have not yet detected the kind of far-distant radio
signals that might suggest such a thing has happened. An answer can
only be found by the discovery of life beyond our planet. And that is
predicated on the discovery of liquid water. In Chapters 9 and 10 we
visit oceans on other planets and explore the possibility for life within
them. First, though, we have to see what the future might hold for the
oceans of Earth.