This week’s challenge is all about forces of nature, so I thought I’d focus on something common, but overlooked: Oxidation. Rust forms when iron comes into contact with things like water and oxygen, and even more so with salt water. This chemical reaction happens everywhere, perhaps most famously with the Statue of Liberty; it was made of copper, but years of ocean weather gave its surface a blue/green patina. If you want something a little more local, try finding an old nail…like this one on my back porch. Large version available here.