Re: Why would paper,and not a plastic or styrofoam,cup rot when I buried them?

Paper is really made out of the same stuff as plants and trees. But plastic and styrofoam (which is really just one sort of plastic) are completely different materials that are made in factories by chemical reactions.

Both paper and plastics are made up of giant molecules, containing millions of atoms all tightly joined together. If they are going to rot, these giant molecules have to be broken down into smaller chunks, with only about ten to a hundred atoms joined together. Rotting is mostly a matter of being eaten by small animals, or fungi(plants), or microbes, in the soil.

There are two reasons why this will happen with paper, and not with plastics. The first is that animals (and fungi, and microbes) use plants for food. So animals have already within their systems various digestive juices and "enzymes" that help break down the giant molecules found in plants. That means they can eat paper as well! But they do not have the right ones to break down the different types of giant molecules found in plastics. After all, plastics have only been around in the environment for the last fifty years or so, so the animals would have had no use for them before that. And animals do not adapt these sort of things quickly, or even in quite that way.

The second reason is simply that the bonds in the giant molecules in plastic are a little bit stronger, and it is a little bit harder to find the right sort of substances that will react to break these bonds. They are not found in the natural environment.

Recently there has been some work done to make plastics that have parts of the structure of their giant molecules more like the structure of wood. These materials are known as "biodegradable" plastics, and they will rot in the environment.