A team of researchers gathered at the Field Museum, Chicago, and took an entire collection of Horned larks to study. By looking at their wings and the dirt and soot trapped on them, they could find out which was the evolution of pollution since the beginning of the 20th century.
Birds kept soot particles on their feathers
The collection gathers specimens of all ages, some of them being even 100 years old. They are special, since their feathers usually gather traces of all pollutants present in the atmosphere, offering a better insight on pollution during the era of the big factories than any models scientists could build. Therefore, thanks to the traces of pollutants present on their wings, they measured the levels of soot present in the atmosphere back then.
The discovery occurred in the 1930s when researchers noticed some birds of the same species had darker feathers than others. They quickly established the darker shade came from tiny particles of soot trapped within the feathers. However, the first time when the discovery was used was almost 80 years ago, while two scientists were analyzing museum collections.
The soot on the feathers built a comprehensive pollution model
They quickly realized they could find out more about the environment of the time by looking at how it interacted with the birds. Since the bird collection was truly vast, containing thoroughly dated specimens from different periods, the scientists could map a comprehensive distribution of soot and other pollutants over a broader area.
They noticed the highest levels of pollutants at the beginning of the 20th century, and a big decline during the Great Depression when the factory activity suffered a massive drop. Then, the pollutant emissions rose again, as World War II started. They matched the observations with well-known historical events and discovered this model is more accurate than anything we had previously designed.
Therefore, they managed to build a better analysis of the soot levels in the atmosphere since 1880 and after World War II, which was published in the journal Proceedings of the National Academy of Sciences.
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