BC Scientists solve mystery of origins of Burgess Shale

Scientists solve mystery of origins of Burgess ShaleRandy Boswell,
Canwest News ServicePublished: Thursday, February 21, 2008

It's been called the world's single greatest assemblage of primeval fossils - an accidental Canadian treasure that scientists literally stumbled upon 100 years ago in B.C.'s Rocky Mountains.

The Burgess Shale fossil site in present-day Yoho National Park is a one-of-a-kind, 530-million-year-old time capsule containing the stunningly well-preserved remains of an entire undersea ecosystem from a crucial phase in the history of life - a lost world filled with dozens of bizarre creatures destined to become evolution's losers, but also with a primitive ancestor of the human race itself.

Now, a team of British and Canadian scientists has solved the long-standing mystery of how the UNESCO World Heritage Site near the B.C.-Alberta border was formed at the dawn of the so-called Cambrian "explosion" of life - a time when the future Canadian land mass was drifting in tropical climes close to the Earth's equator.By looking over hundreds of micro-thin slices of rock taken from the famous shales, the researchers have reconstructed the series of catastrophic underwater landslides of "mud-rich slurry" that killed tens of thousands of marine animals representing hundreds of species, then sealed them instantly - and enduringly - in a deep-sea tomb.

The mass death was "not a nice way to go, perhaps, but a swift one - and one that guaranteed immortality (of a sort) for these strange creatures," said University of Leicester geochemist Sarah Gabbott, lead author of a study published in the U.K.-based Journal of the Geological Society.

Desmond Collins, a Royal Ontario Museum paleontologist and Burgess Shale expert who co-authored the study, described how the steep wall of rock now popular with Rocky Mountain tourists was once a "submarine cliff, with animals living on the sea floor at its foot. Currents rising up the side of this cliff would have brought a great concentration of nutrients, attracting lots of animals to the area."

But over time, massive clumps of muddy silt built up along the cliff would suddenly give way and entomb the creatures below.

"They would have to buried quickly and deeply enough that scavengers couldn't dig them up," said Collins, adding that the oxygen-free depths of the Cambrian oceans ensured the creatures' remains decayed at extremely slow rates.

"It is most unusual," he said, "to find the soft tissues of these animals preserved the way they are."

Among the imprints of animal remains excavated from the Burgess Shale is one called pikaia, an eel-like creature that has been classified as the earliest known, identifiable ancestor of modern vertebrates - including humans.