Almost everything organic decomposes: food, wood, paper, cotton, wool, skin, bone, and leaves. These materials break down because living organisms, primarily bacteria and fungi, produce enzymes that dismantle complex molecules into simpler ones. Synthetic materials like plastic and glass resist this process because their chemical structures are largely unrecognizable to decomposers. The speed at which something breaks down ranges from days for soft fruit to centuries for bone, depending on the material and the environment it’s in.
How Decomposition Actually Works
Decomposition is a team effort between two tiers of organisms. Bacteria and fungi are the primary decomposers. They secrete enzymes that break large organic molecules into inorganic forms like nitrogen and phosphorus, which cycle back into soil and water. But these microbes depend on a second group: soil-dwelling animals like earthworms, mites, beetles, and millipedes. These creatures shred organic matter into smaller pieces, increasing the surface area available for microbial attack. Their waste products also create nutrient-rich microhabitats where bacteria and fungi thrive.
The process generally moves through four stages. First, soluble compounds like sugars and amino acids are consumed quickly. Then microbes work through more complex proteins and starches. Tougher structural materials like cellulose (the main component of plant cell walls) break down next. Finally, the most resistant compounds, like lignin in wood, are slowly dismantled. Each stage involves different communities of organisms and different enzymes, which is why decomposition slows as it progresses through increasingly stubborn materials.
What Breaks Down Fast
Soft, moist, nutrient-rich materials decompose quickest. A paper towel disappears in two to four weeks. Orange peels take two to five weeks. Cotton fabric breaks down within one to five months. Fresh leaves in warm, moist soil can be unrecognizable within a season. Food scraps, animal manure, and grass clippings are similarly fast because they’re high in nitrogen, which feeds microbial growth.
Soft animal tissue, including muscle, organs, and skin, typically decomposes within 3 to 12 years in a burial setting. The timeline depends heavily on temperature, moisture, oxygen, and the surrounding soil chemistry. In warm, humid conditions with active insect populations, soft tissue on an exposed carcass can be reduced to bone in weeks.
What Breaks Down Slowly
Wood, bone, and hair resist decomposition because of their molecular structure. Wood contains lignin, a compound so tough that only certain fungi (white rot and brown rot species) can break it apart. A fallen hardwood log in a temperate forest may take decades to fully decompose.
Bone lasts even longer. Made primarily of a calcium-phosphorus mineral called bioapatite, bone can persist for centuries under the right conditions. Soil acidity is the key factor: even slightly acidic soil (around pH 6.5) begins dissolving bone mineral. In the Northern Great Plains, researchers found that burial soils became significantly more acidic within and below the bone layer compared to surrounding soil, which gradually promotes dissolution. Alkaline, dry soils preserve bone far longer, which is why skeletal remains survive thousands of years in desert and limestone environments.
What Barely Decomposes at All
Conventional plastics, glass, and most metals resist biological decomposition because their chemical bonds are foreign to the enzymes that decomposers produce. A glass bottle in a landfill will outlast any human timescale. Standard plastics don’t biodegrade in any meaningful sense. Instead, they undergo photodegradation: sunlight generates free radicals on the plastic surface that slowly crack and fragment the material into smaller and smaller pieces, eventually becoming microplastics. This isn’t true decomposition. The plastic isn’t being converted into nutrients. It’s just breaking into tinier bits of the same synthetic polymer.
There is some nuance, though. Recent research has found that microplastics can degrade through a hybrid process combining biological and chemical attack. Plastics that have been “aged” by sunlight develop oxygen-containing structures on their surface that allow bacteria to colonize and break them down. In composting environments, aged microplastics degraded about three times faster than fresh ones, with microorganisms responsible for roughly 73% of the breakdown. Still, this is a slow, incomplete process, nothing like the efficient recycling of organic matter.
Why Environment Matters More Than Material
The same leaf that vanishes in weeks on a warm forest floor can survive for millennia in a peat bog or permafrost. Decomposition speeds up with warmth and moisture because those conditions boost microbial metabolism. It slows dramatically when any key ingredient is missing: heat, water, or oxygen.
In permafrost regions, organic carbon that would normally cycle through decomposition in years or decades instead stays locked in frozen soil for centuries. Land surface modeling shows that even if global temperatures stabilize at 1.5°C of warming, it would take high-latitude ecosystems several centuries to adjust, gradually thawing and releasing carbon that has been preserved in frozen ground. Deserts preserve organic material through a different mechanism: extreme dryness. Without water, enzymes can’t function and microbial activity grinds to a halt, which is why mummies and dried plant matter survive thousands of years in arid climates.
With Oxygen vs. Without Oxygen
Decomposition looks and smells very different depending on whether oxygen is present. Aerobic decomposition, the type that happens in well-aerated soil or a properly managed compost pile, produces carbon dioxide, water, and heat. It’s relatively fast and doesn’t produce strong odors.
Anaerobic decomposition occurs in waterlogged soil, sealed landfills, or the bottom of stagnant ponds, anywhere oxygen can’t reach. Instead of carbon dioxide, the primary byproduct is methane, a potent greenhouse gas. Anaerobic organisms also produce hydrogen sulfide and other sulfur compounds, which is why swamps, flooded landfills, and poorly managed compost piles smell like rotten eggs. The process is slower and less complete than aerobic decomposition, which is why organic material can persist for a long time in oxygen-poor environments like bogs.
Composting: Decomposition on Your Terms
Composting is simply managed aerobic decomposition. You’re giving bacteria and fungi the optimal conditions to do their work quickly. According to the EPA, the ideal recipe is roughly three parts “browns” (dry, carbon-rich materials like leaves and cardboard) to one part “greens” (wet, nitrogen-rich materials like food scraps and grass clippings). This creates a carbon-to-nitrogen ratio of about 30:1, which is the sweet spot for microbial growth.
Oxygen is the other critical ingredient. Turning the pile, adding bulky materials like wood chips to create air pockets, or using perforated pipes all help keep the process aerobic. A well-managed compost pile heats up to 130°F or higher, which speeds decomposition and kills weed seeds and pathogens. Without enough aeration, the pile goes anaerobic, slows down, and starts producing the telltale rotten smell of methane and sulfur compounds.