Small Fossil Remembers When Continents Collided
were the mountains of Wales pushed up?
JPEG IMAGE OF THE FOSSIL IS AVAILABLE ON REQUEST: EMAIL HR15@LE.AC.UK
was well before the dinosaurs roamed the earth.
And it happened in the aftermath of a gigantic continental collision,
when England and Wales (then attached to southern Newfoundland) crashed into
Scotland (then attached to north America).
The muds of the sea floor were converted, then, into the hard grey slates
of the Welsh hills.
now it has been very hard to tell exactly when these slates were formed, because
the minerals that make up the slates have been just too tiny for scientists to
be able to separate out and measure their age.
research by paleontologist Jan Zalasiewicz, of the University of Leicester
Geology Department, and colleagues from the Open University and the British
Geological Survey is now able to shed light on this geological mystery - thanks
to some small fossils.
graptolites (see picture right) – mysterious, extinct planktonic creatures – have been found
preserved in the slates, their remains beautifully mineralized in shiny yellow
iron pyrites (fool’s gold).
the muds were crushed into slates, they were deformed around the hard pyritized
spaces opened between the fossils and the rock as this happened, and these
spaces were filled with pure new slate-forming minerals.
minerals were large enough and pure enough for Sarah Sherlock of the Open
University to extract and to date, exploiting their natural radioactivity as a
kind of natural clock.
results show that the slates formed 396 million years ago (plus or minus 1.4
million years). This
is by far the most precise date extracted from the slates of the Welsh hills, or
indeed from slates anywhere in the world.
pioneering method can now be applied to measure the ages of mountain belts
everywhere, since fossils preserved in fool’s gold can be found all around the
NOTE TO EDITORS:
Further information is available from Dr Jan Zalasiewicz, University
of Leicester Department of Geology, telephone 0116 252 3928, fax 0116 252 3918,
This document has been approved by the head of department or section.