Decomposition
Decomposition is when dead plants, food, or other materials break down into soil.
A slice of bread left on the counter slowly turns green and fuzzy. Mold and tiny bacteria land on it and eat the bread apart, piece by piece. Over days, the bread softens, shrinks, and falls into crumbs and dark mush. That dark mush is the same kind of rich material that forms in soil after leaves and plants break down outside.
Explaining decomposition by grade level
Put a carrot in dirt and wait a few weeks. The carrot gets soft and dark. Tiny living things in the soil eat the carrot bit by bit. Over time, the carrot turns into part of the soil.
Projects that explore decomposition
Cold temperatures slow decomposition, so food breaks down into soil at different speeds depending on its environment. To measure this, bury carrot pieces in sealed plastic bags with potting soil. Set up one bag as the experimental chamber and one as the control, then change a single condition between them, such as temperature or soil moisture. Weigh the carrots before and after to see how much has broken down.
Some materials break down into soil over time. Others stay unchanged for years. Fill six plastic bottles with soil, then bury a different material in each one — vegetable scraps, paper, plastic, wood, metal, and styrofoam. Sprinkle water on top and check the bottles every few weeks. Some items shrink and crumble as they decompose. The rest look exactly the same.
What happens to a banana peel, a plastic bag, and a newspaper after you throw them away? Some materials break down into soil in weeks. Others last for centuries. To see the difference, build a compost column from plastic bottles and fill it with soil, fruit scraps, grass, newspaper, and plastic. Over two to four weeks, you observe which items decompose and which stay the same.
Products labeled biodegradable promise to break down into soil, but do they hold up in 30 days? Weigh spoons made from corn starch, wheat-based spoons, and regular plastic ones. Then bury them in moist garden soil for 30 days. After digging them up, weigh each type again and calculate the percentage of weight lost. The results reveal which materials decomposed and which stayed unchanged.