A Sandy Look Into the Past
Measuring the shape of 6,000 sand grains to reveal the history of a landscape.
Just like any good comic book character, landscapes have an origin story. Since no speech bubbles pop out from the soil, learning a landscape’s history requires alternative methods. Now, thanks to scientists, even a grain of sand can enlighten you.
One way to piece together the history of a landscape is to dig down into the soil and look at the layers. They offer a time machine thousands of years into the past, showing us what plants and animals once lived there, and even what the climate might have been like.
But if you dig down into the soil on the northern end of Calvert Island, you soon hit a layer of sand, and the time machine grinds to a halt. Or at least it did until now.
“All the sand below the soil poses a problem to piece together landscape history,” says Jordan Eamer, a PhD candidate and Hakai scholar at the University of Victoria.
Eamer and colleagues recently published a paper in the Journal of Sedimentary Research on their search for an efficient, cost-effective way to find out where that buried sand came from.
“We’re trying to put together how the landscape evolved over 15,000 years,” says Eamer. “We’re doing this to get a snapshot through time of what the coast looked like. A lot of archaeological research is dependent on where the shoreline was over time.”
Was that sand layer part of a dune on the old coastline? Underwater? Part of a coastal beach?
Previous research used time-consuming methods or expensive equipment like a scanning electron microscope to answer questions about a sand grain’s origins. But Eamer and his colleagues set out to do it with far simpler tools.
“We based this method on freely available software and optical microscopes, which are fairly ubiquitous in science labs,” says Eamer.
The software—called ImageJ—can be programmed to manipulate images and automatically detect certain shapes. ImageJ has been used for scientific purposes that range from highlighting thousand-year-old human rock paintings to counting bacterial colonies.
Automating the process was key. Recording the shape of nearly 6,000 sand grains without automation would take untold hours. To standardize the method, they first needed to look at sand grains that they knew came from either a beach or a dune. Using those known samples, the researchers could then determine what consistent attribute of the sand grain matched the location where the sample was collected.
From all that sand, Eamer and his colleagues discovered that the characteristic that best predicts the origin of sand is the grain’s relative roundness—dubbed its solidity.
“A perfect sphere would have a solidity of one,” says Eamer. “If you take a chunk out of the edge, say like a slice of pizza, the solidity decreases. So the more jagged or irregularly shaped an object is, the lower its solidity.”
When it comes to sand, if it’s round, it’s been blown around. Rounder grains came from wind-swept dunes, rather than a beach. With this knowledge, they can now deduce the origin of any buried sand they find and, along with other geological clues, piece together the history of the landscape.
“In the near future, we’re using [this method] to continue to piece together the history of northwest Calvert Island around the Hakai research station,” says Eamer, who added that this knowledge could be used to track how humans migrated down the coast over 10,000 years ago.
And sand isn’t the only sediment on which scientists can use this method; they could also study landslides or debris from tsunamis. Now, with simple equipment and free technology, scientists are going back in time.
Acknowledgements
This research was conducted in collaboration with Dan Shugar (University of Washington Tacoma), Ian Walker (Arizona State University), as well as Olav Lian and Christina Neudorf (University of the Fraser Valley).