In natural ecosystems, there is no such thing as waste. Matter expelled by one organism is taken up by another organism and used again. This natural recycling is consistent with the law of conservation of matter, which states that matter is never created or destroyed; it only changes form. Forms of matter that are dangerous to living things (think arsenic and mercury) tend to stay buried, deep underground, and are released only during extreme events like volcanic eruptions.

Human ecosystems are another story. By taking matter out of the reach of organisms that can use it, we continually disrupt this natural cycle. We do this by converting usable matter into synthetic chemicals that can’t easily be broken down and by burying readily degradable things in places and under conditions where natural processes can’t run their course.

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For example, paper and cardboard break down easily in a compost bin, thanks to the microbes that feed on them. But we typically keep this type of waste in landfills, where the lack of water, oxygen, and microbes force it to decompose much more slowly than it otherwise might.

Thus matter—the physical substance of which the universe is made—becomes waste—a uniquely human term used to describe all the things we throw away. Waste that can be broken down by chemical and physical processes is considered degradable, even if that degradation takes a long time. Waste that can be broken down by living organisms such as microbes is considered biodegradable. Some waste—mostly synthetic molecules like the pesticide DDT and the CFCs once found in aerosols—is considered nondegradable. These molecules are chemically stable and don’t degrade in normal atmospheric conditions. And because they haven’t been around for very long, no organism has yet developed (through mutation or genetic recombination) the enzymes to use them as food.

This explains why plastics—a human creation that uses petroleum or natural gas as the starting material—take so long to fall apart and break down; nothing “eats” them in their original form. Different types of plastics have different degradation rates, but for all it is generally quite slow. After all, one of the perks of plastics is their durability. Exposure to sunlight in an oxygen-rich environment causes plastics to chemically change and become brittle, breaking into smaller pieces and making some (but probably not all) components of the plastic accessible and digestible by microbes. This is an incredibly slow process when plastic is buried in a landfill (with no sunlight and little oxygen), but on beaches and the surface of the ocean, it can occur more quickly due to the exposure to sunlight and the additional weathering action of wind and waves, which produces the tiny plastic bits found in the ocean garbage patches.

Almost any human activity you can think of generates some form of waste. Processes that produce food and consumer goods generate agricultural and industrial waste, which in the United States account for about 54% of all garbage. The harvesting of coal and precious metals like gold and copper generates mining waste, which can pollute air, water, and soil and makes up an additional 33% of U.S. waste. And the increasingly complicated act of living—in houses, apartments, dormitories, and small businesses around the world—produces its own steady stream of trash, referred to as municipal solid waste (MSW), or at the community level, an MSW stream. INFOGRAPHIC 7.1

Currently, urban dwellers produce about 1.3 billion metric tons (0.9 billion U.S. tons) of solid waste each year and this amount is expected to almost double by 2025. In the United States, MSW streams make up just 2% of total waste. But because Americans create more garbage per person than just about any other country in the world, 2% is still a lot of trash. In 2012 alone, each American produced about 1.99 kilograms (4.38 pounds) of solid waste per day, up from about 1.22 kilograms (2.7 pounds) per day in the 1960s. With more than 300 million people living in the United States, this adds up to about 251 million tons of household trash per year; that’s twice the per capita amount produced by the European Union and as much as 10 times the amount produced by most less developed countries.

The vast majority of this garbage comes from a familiar array of goods: paper, wood, glass, rubber, leather, textiles, and of course plastic—cheap enough to have become a staple of both advanced and developing societies, light enough to float, and durable enough to persist for hundreds of years across thousands of miles of ocean.

In 2012 alone, each American produced about 1.99 kilograms (4.38 pounds) of solid waste per day.

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