CT scans offer a new way of looking at fossils


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FOR YEARS, scientists have been chipping away at rocks and other formations looking for fossilized remains of plants and animals from millions of years ago.

The impression of a millipede set in mudstone. (TIM KROCHAK / Staff) The problem is the chipping, even if done carefully, can destroy tiny fossils, and taking out a slice of rock may not help because a fossil could be inside the slice.

A possible solution was brought to light recently at the Joggins Fossil Centre when some doctors were touring the UNESCO World Heritage Site and asked a guide if anyone had ever used a CT scanner, more commonly used to take images of the human body in hospitals, to look inside the large hunks of old rock and fossilized trees at the site.

The guide was Matt Stimson, a student at Saint Mary’s University. Now researchers at the university are looking into whether CT scans would work when looking at fossilized trees containing fossils of small lizard-like creatures and other species.

The trees were burned in ancient fires and then became hollowed-out stumps before fossilizing into solid pieces with the remains of small creatures inside.

Research using CT scans of fossilized trees has been started at SMU by geology professor Andrew MacRae, with help from Stimson, fellow student Brian Herbert, faculty member and Natural Resources Department staffer John Calder, and Don Reid, a Joggins resident who has been collecting fossils at the site for decades.

Saint Mary’s University geology professor Andrew MacRae displays a lycopod tree stump at the university. (TIM KROCHAK / Staff)MacRae said some research was conducted years ago with CT scanners but the technology wasn’t good enough at the time to produce much more than a blob on the screen.

Being able to study fossilized trees and the remains of the tiny lizard-like creatures and other species inside them without destroying the samples would be a significant advancement, he said.

“No matter how small you make the pieces, there are still going to be things embedded,” MacRae said. “The bones are very tiny. They can be a centimetre long, with details that are less than that, so even if you slit a piece of rock into centimetre-thin layers, there could still be things embedded in there that you don’t recognize.”

MacRae said the CT scanner not only lets scientists know where the smaller fossils are, inside the larger piece, but also how they are distributed — in multiple layers or along the inside edge of the trees or whatever. “You can’t get a sense of that when you have multiple surfaces,” he said.

Knowing the arrangement of material within the fossils is important in determining what kind of events affected the creatures — whether the tree stump was their home or just somewhere they went to try to escape a fire, and whether it was a long-term habitat.

“If you were to find individual skeletons at several different levels covered by sediment with intervening layers that don’t have any, that’s suggesting that the stump was a scene for preservation over a prolonged period of time,” MacRae said.

Saint Mary’s University geology professor Andrew MacRae studies a petrified tree retrieved in the Joggins area. (Tim Krochak / Staff)He said being able to learn about the habitat of the creatures is important because they are at the root of the development of modern-day reptiles, mammals and birds.

“If you want to understand how the Earth will respond to change, the best thing to look at is the history of change,” he said.

The first CT scan in the current project was conducted at the research facility of the Queen Elizabeth II Health Sciences Centre in Halifax on a small piece of tree that had one bone visible and the tip of another showing. The scan revealed several pieces within the sample that couldn’t be seen just by eyeballing it.

What MacRae wants to see next is a scan of a fully preserved stump weighing more than 200 kilograms.

But that will require an industrial scanner, like those used to check airplane engines.

That will mean time and money, and while he is encouraged by the results of the smaller test, he said it will likely be two years before the stump can be scanned and studied.

Analyzing the images will then take another couple of years.

“Our little experiment has worked,” MacRae said, “but there are issues with the penetration of the X-rays, and there are a lot of technical details to sort out before we know if this will work.”

Author: Ian Fairclough | Source: The Chronicle Herald [December 31, 2010]



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