How soil shatters like glass, and what that means

Odds are, you’ve dropped a drinking glass once or twice, and it’s shattered into lots of little pieces. Believe it or not, the same thing happens when sand impacts tiny particles in soil: the soil particles “shatter” into even tinier bits of dust. A new study by Jasper Kok at the National Center for Atmospheric Research (NCAR) in Colorado sheds light on the particular patterns into which those soil particles shatter. Experts say his findings might help scientists understand how Earth’s climate is changing.

Why climate change? Shattering particles on the ground – such as particles in soil – can produce dust that rises up into the atmosphere. Depending on their size and composition, some bits of dust reflect the sun’s heat, and some bits of dust trap the sun’s heat. Hence, dust’s impact on climate.

Up until this point, scientists haven’t been able to figure out precisely which types of dust – heat-reflecting or heat-trapping – are flying around in the atmosphere, and in which amounts. So, nobody can effectively estimate the degree to which dust is heating or cooling the globe. Enter: Dr. Jasper Kok.

Kok’s recent investigation, published this week by the National Academy of Sciences, focused on mineral dust. This type of dust is formed when grains of sand are blown into soil all across Earth. The sand shatters the dirt and sprays the resulting dust into the air. As the National Science Foundation (NSF) reports:

The smallest [dust] particles, which are classified as clay and are as tiny as 2 microns in diameter, remain in the atmosphere for about a week, circling much of the globe and exerting a cooling influence by reflecting heat from the sun back into space. Larger particles, classified as silt, fall out of the atmosphere after a few days. The larger the particle, the more it will tend to have a heating effect on the atmosphere. Kok’s research indicates that the ratio of silt particles to clay particles is two to eight times greater than represented in climate models. Since climate scientists carefully calibrate the models to simulate the actual number of clay particles in the atmosphere, the paper suggests that models most likely err when it comes to silt particles.

What does this mean? Just that Kok is pretty sure the majority of dust in the atmosphere is larger in size than scientists previously thought. That’s helpful for climate scientists to consider, because bigger dust particles will tend to exacerbate warming on Earth, rather than relieve it.

Kok, savvy scientist that he is, figured this out by applying old formulas describing the fracture patterns of brittle objects to soil measurements. In other words, he combined known physics formulas on how a material like glass shatters with data on the amount of soil across Earth being bombarded by sand grains. Again, from the NSF press release:

Physicists have long known that certain brittle objects, such as glass, rocks, or even atomic nuclei, fracture in predictable patterns. The resulting fragments follow a certain range of sizes, with a predictable distribution of small, medium, and large pieces.

By cleverly applying an old idea to a new(ish) problem, Dr. Kok and his team appear to have pinpointed more accurately than ever before the size distribution of dust particles in the atmosphere.

“The idea that all these objects shatter in the same way is a beautiful thing, actually,” Kok says. “It’s nature’s way of creating order in chaos.”

Related: Oliver Chadwick on why there’s more dust in Earth’s atmosphere