There’s a view over a waterfall, which crashes down into a narrow valley.
A few yards farther up the path there’s a jagged outcropping of rock,
which is striped vertically, like an umpire’s jersey, in bands of light and
dark. Jan Zalasiewicz, a stratigrapher from the University of Leicester,
sets his rucksack down on the soggy ground and adjusts his red rain
jacket. He points to one of the light-colored stripes. “Bad things happened
in here,” he tells me.
The waterfall at Dob’s Linn.
The rocks that we are looking at date back some 445 million years, to
the last part of the Ordovician period. At that point, the globe was
experiencing a continental logjam; most of the land—including what’s
now Africa, South America, Australia, and Antarctica—was joined into one
giant mass, Gondwana, which spanned more than ninety degrees latitude.
England belonged to the continent—now lost—of Avalonia, and Dob’s Linn
lay in the Southern Hemisphere, at the bottom of an ocean known as the
Iapetus.
The Ordovician period followed directly after the Cambrian, which is
known, even to the most casual of geology students, for the “explosion”
of new life forms that appeared.* The Ordovician, too, was a time when
life took off excitedly in new directions—the so-called Ordovician