Ocean Forms - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 58

metal. He returned to his family's farm at Slighhouses in the Scottish
Borders in 1754. Hutton had also developed a passion for natural his-
tory, partly inspired by the Comte de Buffon's Histoire Naturelle . The
wages of sin of his exile were a mind able to ponder the age-old secrets
of the Scottish mountains, and to develop insights that would change
how people viewed the Earth and its history.
Walking among the rock strata, Hutton saw that sea floors eventu-
ally became uplifted and crumpled to become mountain ranges—and
that when these were eventually worn down, the sea crept back. In
realizing the scale of time necessary for these kinds of things to take
place, he stumbled upon the tangible reality of deep geological time.
Indeed, he thought of the process as eternal and endless, considering
the Earth to have 'no vestige of a beginning, and no prospect of
an end'.
We now know, though, that there was a beginning to the Earth,
some 4,567 million years ago, as its main bulk accreted from colliding
planetesimals (astonishingly, this figure seems to be precise to the
nearest million years). The question about beginnings therefore
becomes more nuanced. Have the oceans and continents simply been
engaged in this stately dance since, for instance, plate tectonics began,
or has the nature of the dance (and indeed of the dance floor)
changed?
More precisely: has the proportion of oceans and continents always
been more or less the same? Or, have the continents grown and
expanded on a world that used to be mainly ocean? Or have the con-
tinents shrunk and the oceans grown?
This has been—and remains—debatable. Current opinion is that,
through Earth history, the continents have grown overall at the
expense of ocean crust. One line of evidence is the general structure
of the continents, which—to a very crude approximation—are made
up of an ancient central core surrounded by younger mountain belts.