By dating samples of rocks from onshore lava flows where
magnetic reversals had been identified, a time scale of magnetic
reversals was gradually built up until eventually it became
possible to 'read' the ages of the reversals on the sea floor.
Immediately it became clear that the youngest rocks were near-
est to the ridge, while the oldest were furthest away and adja-
cent to the continents. Either side of the ridge, stripes of exactly
the same age could be matched up with one another. So the
oceans really were opening, and the continents really were drift-
ing apart. Wild miracle confirmed! Continental drift at long last
became a reality.
Within a couple of years, and certainly by the end of the 1960s,
a revolution had occurred in the earth sciences, and there were
only a handful of geologists left who still did not accept
the 'new' ideas about sea-floor spreading and continental drift.
The key to that revolution was development of a geological time
Today geology has its dates, just like history does. Time has
become the framework onto which we hang all geological events
and, as in our daily lives, it has become indispensable. We have
learnt how to tell geological time from isotopic clocks, and
we have developed a time scale for the evolution of life, and all
that went before it. Using the clocks and the time scales we have
discovered the true age of 'Mother Earth', revealed many of her
internal mysteries and developed a unifying theory that explains
all geological processes - just as Arthur Holmes' vision of 1913
said we would:
With the acceptance of a reliable time-scale, geology will
have gained an invaluable key to further discovery. In every
branch of the science its mission will be to unify and corre-
late, and with its help a fresh light will be thrown on the more
fascinating problems of the Earth and its Past.
Given enough time, everything possible happens.