Fuck Yeah Zoology

The Science Behind the Burgess Shale

Scientists were stumped by how the fossils in the Burgess Shale were so well preserved up until a few years ago. It turns out that the type of rock the fossils were buried in typically builds up slowly over time – clearly was not the case for this instance. Scientists found that mud slurry from the oceanic floor buried these animals really quickly, preserving soft body parts when they would have decomposed otherwise. Because they were instantly buried, scavengers couldn’t eat away at the soft parts, and bacteria are not active at that level.

During the formation of modern day continents, tectonic plates smashed together and then drifted apart. This chaotic crust movement eventually would form the Rocky Mountains. During the Cambrian era, North America was shifting up from the equator, and the west coast was facing north. At this time, the coast was about where Calgary, Alberta is (where I live). The Burgess Shale quarry was underwater just below a huge cliff, which was also underwater at the time. The sea base was, of course, mud and periodically mud would rush into the quarry via storms and bury the inhabitants. The ocean basin filled with mud which formed shale; however the section was still underwater. Sections of the sea floor were crushed against each other; the result was older rocks being raised above younger rocks, and thus the Burgess Shale ending up “on top” so to speak. Western and central British Columbia formed by small islands and rocks colliding with the mountains holding the Burgess Shale, raising it further above the water.

The area has been greatly modified from its original state due to erosion, and the Burgess Shale is exceedingly hard to get to, being on top of fittingly named “Fossil Ridge” on the boarder of British Columbia and Alberta.

What is the Burgess Shale?

As we all know, it’s very rare for an animal to leave fossil remains, and when they do, it’s often just barely. Most fossils in museums (unless you visit the Smithsonian or London Natural History Museum) are casted replicas, or something called “replacement fossils”, which means the carbon has been replaced with minerals. This is partly due to the fact that fossil remains are really in not very good condition. Many times, the carcass itself has decomposed completely, leaving only an imprint in the rock. To find a fossil in very good condition would mean that it is either very young or extremely rare and valuable.

Despite this rarity, there happens to be so many animals buried in sedimentary rock that finding one isn’t exactly uncommon. Think trillions of animals lived and died, with millions leaving fossils. The percentage is minute, but the numbers aren’t that small.

Now, we are all aware of the Cambrian Explosion, right? It is a period of time in which a great diversity of animals evolved when before there was no such diversity. How lucky would it be to find Cambrian fossils (530 million years old) in excellent condition?

The condition in one small section of the Canadian Rocky Mountains in British Columbia is astonishingly perfect. This spot is called the Burgess Shale. It contains fossils from the Cambrian era which are so well preserved; in some fossils you can see the contents of an animal’s stomach. Not only are hard-bodied fossils found in the Burgess Shale, but amazingly, soft-bodied invertebrates as well. Suddenly, we have a massive amount of information about the history of a huge population of organisms.

Think about the age of these fossils for a minute. 505 million years. Compare them to many dinosaur bones which, let’s be honest, are kind of falling apart, and they are somewhere around 250 million years old. Fossils more than twice as old in the Burgess Shale are easily twice as preserved.

Despite the amazing circumstances of the Burgess Shale, nobody talks about it. A tumblr search brings up a measly eight results. I hope to expand that number as well as extend my excitement for the Burgess Shale to others over this coming week.