Peat is a dark, spongy material made from partially decomposed plants that have been compressed in waterlogged areas over thousands of years. In bogs and wetlands, dead moss, grass, and other plant matter sink into stagnant water where they decay very slowly because there's not enough oxygen. Layer after layer builds up, creating thick deposits of peat that can be cut into blocks, dried, and burned as fuel.

For centuries, people in Ireland, Scotland, and other northern regions have harvested peat from bogs to heat their homes and cook their food. When dried peat burns, it produces a distinctive earthy smell and gives off steady heat. Peat was especially important in places where trees were scarce and coal wasn't available.

Peat bogs are also fascinating time capsules. Because peat preserves things so well, archaeologists have discovered ancient tools and even remarkably preserved human remains thousands of years old in peat. Scientists study peat bogs to learn about past climates and ecosystems.

Today, gardeners use peat moss (partially decomposed sphagnum moss) to improve soil, though this practice is controversial because harvesting peat destroys important wetland habitats and releases carbon that has been stored for millennia.