It’s not easy to extract iron from its ore. But the peoples of the ancient city of Great Zimbabwe—the capital of a thriving kingdom in southern Africa between 1000 to 1700 AD—were masters.

At sites near the city’s stone ruins, clusters of iron-smelting furnaces survive today as mounds of rubble. At Mashava, a village 25 miles northwest, fragments bear fingermarks of those who long ago smoothed the structures’ clay interiors.

Some of the furnaces were nearly an adult’s arm span in width, with walls thick and strong to contain the heat of more than 2,100° Fahrenheit needed to smelt iron. Unlike other furnaces that required workers to force air into them with bellows, these were designed to suck air in, then out through a chimney, no human labor required. This would have made it significantly easier to produce the iron, which was fashioned into hoes, axes, and arrowheads.

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It’s a regrettable reality that there is never enough time to cover all the interesting scientific stories we come across. So every month, we highlight a handful of the best stories that nearly slipped through the cracks. October’s list includes an epigenetic mechanism for why large dogs age faster than smaller ones; physicists who trapped a single particle of antimatter for months; and invisible tattoo inks that only show up under UV light.

Why large dogs age faster

In many mammalian species, larger creatures tend to have longer lifespans. Mice, for instance, live an average of just two years, while some whales can last for as long as 200 years. Dogs, however, buck this pattern; larger dogs tend to age faster and die younger than smaller ones, which makes canines an ideal model for biologists to study to learn more about aging in general. Arizona State University scientists report that these lifespan differences seem to be due to so-called "jumping genes," according to a paper published in the journal Science.

The authors used data from 864 dogs collected in the Dog Aging Project to map patterns of DNA methylation (which influences how much certain genes are turned on or off) across the entire genome. It's part of the epigenome, whose markers can change over time in response to stress and other environmental factors. Genetic sequences, by contrast, are largely fixed. So DNA methylation is a good chemical indicator of aging and DNA regulation.

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