Geoscience Reference
In-Depth Information
There are seven principal plates: the African, Eurasian, North American, South American,
Pacific, Indo-Australian, and Antarctic plates.
13. The major tectonic plates of the world and their boundaries.
There are also a number of smaller plates, including three quite substantial ones around the
Pacific, plus some more complicated fragments where other plates join.
Another of my childhood memories is of tracing the continents from an atlas, cutting them
out and trying to fit them together as a single land mass. This must have been about the
time of Tuzo Wilson's paper in
Nature
in 1965. I can still remember the thrill of finding
how well they fitted and of discovering some of the reasons why the fit was not perfect. It
was not just down to my inaccurate tracings. As any nerdish schoolboy knows, you have
to cut the continents at the edge of the continental shelf rather than at the coastline. And
you can cut off the Amazon delta which would otherwise overlap with Africa, since that
has grown since the split of the continents. More exciting was discovering that North and
South America need to come apart to make a fit, and that Spain must part company from
France. Swinging it back bangs Spain into France exactly where the Pyrenees are today. So
could such continental collisions be the cause of mountain ranges?
It was at about that time in my teenage years that family holidays took me to the Pyrenees
and to the Alps. In places I could see the layers of sedimentary rock not lying flat as they
did in less disturbed lands but rucked up like a carpet into folds and undulations. This took
my thoughts back to marmalade. As the conserve simmers, you keep a china plate in the
fridge. Every few minutes you bring it out and drip a few drops of the hot marmalade on
