Geoscience Reference
In-Depth Information
were undergoing their own revolution at the same time. The concept of plate tectonics was
at last gaining acceptance, 50 years after Alfred Wegener originally suggested it. Explor-
ation of the ocean floor revealed that it was spreading out from a system of mid-ocean
ridges. It had to be going somewhere, forcing continents apart or into one another. The un-
imaginable masses of continent-sized plates of rock were on the move in an elaborate and
ancient waltz.
It was around the same time, and with the same icon of that small blue jewel we call Earth
floating in the blackness of space, that a global environmental movement began to form, a
mixture of those with a sentimental attachment to endangered species and rainforests and
scientists taking on board a new view of complex, interacting ecological systems. Today,
most university departments and research groups use the term 'Earth sciences' rather than
geology, recognizing a broadening of the discipline beyond the study of rocks. The term
'Earth systems' is becoming widespread, recognizing the inter-related, dynamic nature of
processes that include not only the solid, rocky Earth but its oceans, the fragile veil of its at-
mosphere, and the thin film of life on its surface as well. It is as if our world were an onion;
a series of concentric spheres, from magnetosphere and atmosphere, through biosphere and
hydrosphere, to the layers of the solid earth. Not all are spherical and some are much less
substantial than others, but each manages to persist in a delicate equilibrium. Each com-
ponent of such a system is seen not as something fixed and unchanging but more like a
fountain; maintaining its overall structure perhaps, but constantly changing as material and
energy pass through it.
If rocks could talk
Rocks and stones are not the most forthcoming of storytellers. They have a tendency to sit
there gathering moss, only rolling when pushed. But geologists have ways of making them
talk. They can hit them and slice them; squeeze them, squash them, strain and stress them
until they crack - sometimes quite literally. If you know how to look at them, rocks can
tell you their history. There is the recent history of the rock on the surface: how it has been
weathered and eroded; the tell-tale scars of wind, water, and ice. There can be deeper scars
that record periods of heat and pressure and deformation when the rock was buried. Where
these changes are extreme the rocks are known as metamorphic. Then there are clues to
the origin of the rocks. Some show signs of having once been molten and pushed up from
deep within the Earth to erupt out of volcanoes or to intrude into pre-existing rocks. These
are the igneous rocks. The size of mineral grains within them can reveal how quickly they
were cooled. A large mass of granite cools slowly so that crystals in it are large. Volcanic
basalt solidifies rapidly and so is fine-grained. Rocks can be made of the ground-down re-
mains of previous rocks. Here, the size of the fragments tends to reflect the energy of the
