Peat, the ingredient that makes bagged soil light and spongy, comes from wetlands. It can increase the amount of water soil holds onto while also, paradoxically, increasing its drainage ability — creating an ideal environment for nurturing plants. But while it does all of those things, extracting it is problematic because it strips the bogs it comes from of their carbon stores, and hinders their ability to keep storing carbon — both important parts of fighting climate change. Caitlin Petro, a research scientist in the School of Biological Sciences who studies peatlands and the plants in them, explains that it can take millennia for just a few feet of peat to form.