The world all around us is teeming with microorganisms, which are also called microbes. Microbes may be invisible to the naked eye, but their appetites are evident, as they initiate and accelerate the decomposition of all sorts of organic matter, from newspaper, to animal droppings, to pizza crusts and much, much more.
There are many types of microbes working the magic of decomposition. They include bacteria, fungi, protozoa, algae, actinomycetes and others. Different types of microbes work their magic in different ways and they digest different materials, but they all contribute to the breakdown of organic matter, which can also be called biodegradation.
Environmental factors play a vital role in any decomposition process. The presence of water, light, heat, oxygen and other variables all affect the way microbes and their energy sources (see: food) interact.
Oxygen levels in particular greatly impact degradation. Your backyard compost pile is an example of aerobic environment, meaning that oxygen is present. A monstrous landfill, on the other hand, is an anaerobic environment, or one that largely lacks oxygen exposure.
In an aerobic setting, microbes use acids and enzymes to convert the large molecules of a material and into smaller and smaller compounds. After the molecules reach smaller size, microbes can absorb the material and use it for energy.
The same process occurs in anaerobic conditions, but with notably different byproducts – the microbes produce a lot of methane and carbon dioxide. Landfills with methane recovery equipment can capture the gas and sell it to local energy companies; others simply burn off the gas so that it doesn't contribute to greenhouse gas emissions.
Water is even more important than air. Without water, life on Earth wouldn't exist as we know it. The same concept applies in landfills. Landfills with higher moisture levels exhibit much faster biodegradation, while those in drier regions aren't nearly as biologically active.
Yet even when water is plentiful, impermeable conventional plastics are like kryptonite to microbial ka-pow. Plastics tend to resist and deflect just about all of nature's attempts to deconstruct them. Keep reading and you'll see why plastics are so stubborn and tough to break apart.