Thursday, 30 July 2009

The Burgess Shale

Once the Canadian Rocky Mountains were opened to exploration, tourism and mountaineering by the Canadian Pacific Railway, they became a magnet for geologists looking to better understand the earth and her history. One of the CPR's most troublesome spots through the mountains was the Kicking Horse Pass in today's Yoho National Park. To get over the pass and back down required an unforgiving 4.5% grade of track that dashed many steam engines at its base. To make it over "The Big Hill", dining cars would have to be detached and an extra engine attached to the front. It was also the pass that provided some of the most fruitful places for palaeontological discovery, not only for Canada but for the world.


The Big Hill


The first was a find by R.G. McConnell of the Geological Survey of Canada on the slopes of Mt. Stephen. Coming through in 1886 - a year after the completion of the railway - he found a remarkable bed of trilobite fossils that are still a valued resource. It was this which led Smithsonian Institution geologist Charles Doolittle Walcott to the Kicking Horse Pass area in 1907. He published his study of the Mt. Stephen Trilobite Beds in 1908 while the CPR were working on a solution to the problem of the Big Hill.

That solution came in 1909 with the engineering feat known as the Spiral Tunnels, which reduced the grade to a manageable 2.2% by cutting a figure eight of tunnels clear through the mountains. At the end of that same season, Walcott was continuing his survey of the surrounding talus slopes when his horse was halted by a large stone blocking the scant trail. Dismounting, Walcott inspected the boulder and saw it encrusted with a myriad of heretofore unknown types of fossil invertebrates. Promising to return, he resumed excavations on the ridge above the fall and spent the next 14 years unravelling its mysteries.


Walcott at the quarry that bears his name.


What he found was a site beyond significance. It has also taken the century since its discovery to understand what it means. The short form of the work of numerous scientists including Walcott, Harry Blackmore Whittington, Derek Briggs, Simon Conway Morris, Desmond Collins and Stephen Jay Gould is that the Burgess Shale represents one of the earliest stages in the great radiation of multicellular life. It is a window in stone onto that distant period a half-billion years ago when simple organisms evolved into every phylum of animal life known today and many classes that have left no modern descendants.

A unique trick of preservation allowed for this unparalleled site. Though today the quarries of the Burgess Shale sit high above the treeline overlooking the magnificent valley of Emerald Lake and Emerald Glacier, 500 million years ago it sat at the base of an ocean reef. As parts of the reef broke off, they cascaded to the bottom of the shelf along with the creatures luckless enough to be on it at the time. There, the waters were so deep as to be devoid of oxygen and scavengers, permitting the soft-bodied organisms to be gently covered by the silts that became the Burgess Shale.

Those creatures are a druggist's menagerie of the weirdest things ever to populate the earth. For a time it was thought that several represented completely new types that had no correlates in the known world. Further research has suggested otherwise, but has not diminished their oddity. The most dramatic example are the class of very primitive arthropods known as the Dinocaridida. The first one described and presented in the late 1970's reappraisal of the Burgess Shale was the Opabinia, which was received with howls of laughter by the academic symposium. A diminutive segmented arthropod, it was distinguished by its five stalked eyes and claw-bearing proboscis.

The most famous of the Dinocarids is the true monster of the Cambrian Era: Anomalocaris. At a metre long it was frightening animal by any standard, but moreso in its own time when the average creature was only an inch or a half. Unlike the Opabinia, Anomalocaris only had two stalked eyes and made up for that by having two sets of claw appendages shovelling food into its crushing, plate-like jaws. When first discovered by McConnell, the claws of Anomalocaris were originally thought to be shrimp. The length of its body was fringed by lobes or fins which propelled it through the water and pushed water through its gills.


Anomalocaris and its prey.


Some of the Burgess Shale's creatures are still mysteries. Hallucigenia, a thing that looks as its name implies, continues to cause headaches, even in something as simple as trying to figure out whether its ridge of paired spines are pointed up for protection or down for walking on. Others are like looking on our own family tree. The first chordate, Pikaia, the ancestor to vertebrates and to human beings, is known from here.

Such a site of significance also spurred on philosophical debate. In his work Wonderful Life, eminent late scientist Stephen Jay Gloud stated that it supported the conclusions of his philosophical thought experiment of "contingency", which asserts that human evolution is a product of random forces that could not be repeated were time to be replayed. By contrast, Burgess Shale describer Simon Conway Morris as emerged as one of the prominent "middle road" scientists like Francis Collins who are critical of both Creationism and Materialism, asserting in Crucible of Creation that evolution demonstrates a predictability that may be evidence of purpose.

Celebrating its centennial in 2009, the Burgess Shale continues to astonish as one of the best and most important views onto those lost and distant ages of long, long ago.

3 comments:

George Taylor said...

Nice!

You made me learn without me realizing that I was learning!

Kudos!

SO, there is something in Canada besides Martin Short, hockey and snow? ;)

Cory Gross said...

Good Lord, what are they teaching you people at EPCOT?!?? ^_^

Decker said...

Fascinating.
The Burgess Shale reveals a truly alien world. Invertebrates can produce rather inventive permutations when they occupy pretty much every niche. Glad you brought this era up, it definitely helped kick start some creative ideas in me.