GIRI reveals delicate fossils – by grinding them away
Cloudina was a thin-shelled sea creature that existed about 545 million years ago, and many scientists believe that it played a major role in building the first reefs. Princeton University geoscientists Adam Maloof and Akshay Mehra, however, think otherwise – and they do so because of a unique rock-grinding machine.
Due to the fact that Cloudina fossils are so delicate, they can't simply be chipped out of the limestone matrix in which they're embedded. Additionally, because they're of the same density as that limestone, they won't show up in X-rays of the rock. That's where the Princeton Grinding Imaging and Reconstruction Instrument comes in.
Known as GIRI for short, work began on the tool five years ago.
It uses a diamond wheel to grind away very thin layers of the rock (fossils included), taking super-high-resolution photos of the exposed rock face after each layer is removed. When those photos are all run together, users are taken on a virtual 3D trip through the rock, seeing all the fossils in their original orientation to one another.
The rock can be viewed from any angle, and by applying machine-learning algorithms to the images, it's even possible to visually remove the limestone so users see nothing but the fossils.
Each layer can be as thin as a few microns, with both the resolution and the total processing time increasing with the thinness – it takes approximately 90 seconds to cut and image one layer of an average-size sample, which is considerably shorter than the seven minutes that was previously required. With GIRI running 24 hours a day, a typical inch-thick 1,500-slice sample can be processed in about a day and a half.
Since the process is destructive, it's typically not used on rare specimens. Fortunately for Maloof and Mehra, Cloudina fossils are plentiful. And when the scientists used GIRI to analyze the manner in which some such fossils where deposited, they came to the conclusion that Cloudina may have been a reef-dweller … but not much of a reef-builder.
A paper on their research was recently published in the journal Proceedings of the National Academy of Sciences.
Source: Princeton University