Take a deep breath. In a single intake of air, your lungs swell with roughly 25 sextillion molecules, ranging from days-old compounds, to those formed billions of years in the past. In fact, many of the molecules you're breathing were...

From 'smoky fog', smog is a form of pollution often associated with cities.
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A Twig Science
Glossary Film.
Key scientific terms defined in just 60 seconds using stunning images and concise textual definitions....