Very old rocks and a shrimp!

Saturday, May 24, 1997

Shane Wilkinson
2A Earth Sciences

When you think of a laboratory, images of glass tubes, gurgling liquids, and scientists in white lab coats studiously taking notes may be some of the images which come to your mind. They certainly were some of the stereotypes I took with me when I started work in the Geochronology labs at the Geological Survey of Canada in Ottawa in January 1996 (known commonly as the "GSC"). While it's true that some of the time the lab work I was involved with did include gurgling liquids and white lab coats, my preconceived notions of what laboratory work is all about were quickly shattered.

On my first day, I found myself put to work in a zircon picking lab where I would spend much of my first four months meticulously digging through small dishes of crushed rock material to find the best zircon crystals and set them aside to be used to determine the age of the rocks from which they formed in. These tiny crystals, small enough to be dwarfed by my pin-tip sized tweezers, were the start of a long complicated procedure which helps provide geologists with some very powerful information.

Zircon is a mineral that forms as small microscopic crystals in hot magma as it cools (magma is molten rock, similar to lava, which is magma that has spilled out onto the surface of the Earth). If the conditions are just right, zircon crystals will "grow" as the liquid rock cools, and at about 600 degrees Celsius, small amounts of uranium will get trapped inside the crystal structure. One of the amazing properties of this trapped uranium is that overtime, some of it will start to change into lead. Since it is known how fast this process happens, by measuring these tiny amounts of lead and uranium it is possible to determine how long ago the zircons were formed and thus the age of the rock.

Preparing zircons for dating is a long, tedious process which involves many hours sitting at a microscope digging only tiny amounts of crushed rock. It may take as much as 40 kilograms of rock to provide enough zircons to get a reliable date! However, it is a vital step in the whole process which must be done, no matter how difficult it may be to stare in a microscope for a whole day!

While picking zircon crystals from all over Canada, from the coast of Labrador to the Northern edge of the North-west Territories, I had the opportunity to chat with geologists doing the exact same thing I was doing, picking their own zircons. It was during some of these talks that I learned a lot about geology; it was like having several professors and myself the only student! The information I received came in the form of a two-way conversation, with myself able to ask many questions, rather than a lecture with hundreds of students and only one professor.

Near the end of my four-month work term, I was offered an amazing opportunity to work for another four months in another lab at the GSC, which also dates rocks, but with a different method. This lab uses a machine called a SHRIMP, or a Sensitive High Resolution Ion Micro Probe. It is only the third one ever built in the world, and the first one ever outside of Australia. Costing almost as much as ten Ferraris, this machine can actually determine a different age for different parts of a zircon, something which was previously impossible to do by conventional dating methods. This allows a geologist to interpret when the rocks in question may have been partially re-melted under stress and heat as the face of our Earth was forming into what we can see today.

Along with the privilege of running the SHRIMP and being a part of the project, I was fortunate to be a part of another, and just as exciting, project. Far away in the North-West Territories, there is a group of rocks known as the Acasta Complex. The Acasta rocks are the oldest known rocks in the world, with an age of nearly 4 billion years old, as determined by one of the SHRIMP machines in Australia. It was my job to pick and prepare the zircons from the Acasta complex to be dated on Canada's SHRIMP. It was the most exciting zircon picking ever, as I could be holding 4 billion year old zircons in my tweezers!

I returned to the University of Waterloo to continue working on my Earth Sciences degree last fall after 8 months at the GSC, taking with me some unique and exciting experiences. I have received two more surprising bits of information from the geologists at the GSC since my return. The first information came to me in an e-mail message from my supervisor, who also heads up the SHRIMP project. Since my work term, they may have found some zircon crystals that I picked that are actually older than 4 billion years old! The other good news from Ottawa is that I have been invited this coming summer to work as a student assistant to the geologist who is working on the Acasta complex. This would involve a few weeks of lab work followed by a few months of field work in the North West Territories!

My laboratory work at the GSC turned out to be more than white coats and glass-tubing; - rather it started me on an adventure in geology that continues to bring surprise and raise more interest and intrigue as I continue to learn. Before you jump to any ideas the next time someone talks about working in a lab, remember that it may be more than what you think!