I had the pleasure of driving by a city dump the other day and looking at the mounds of garbage got me thinking (as garbage often does): with such a huge amount of garbage piled together, wouldn’t it take quite a while for garbage in the middle of the pile to decompose. If you threw a single piece of garbage on the ground, wouldn’t it break down quicker due to greater exposure to the weather, surrounding environment, etc???
No. Bacteria do most of the work breaking down garbage. They work best where it’s dark wet and warm, such as in a compost pile.
It depends on the material; an apple core would probably be gone by the next day (not through decomposition though, of course), a washing machine wouldn’t.
BTW, dtilque; landfills are so large and compressed as to be pretty much anaerobic AFAIK.
I would think it depends on what the garbage is made of. Organic materials should decompose nicely if you put them in a big pile – that is rather the point of compost heaps.
As far as plastics go, from this site:
…backing up a bit, does the term garbage mean specifically organic (in the non-chemist definition) waste? (as distinct from ‘trash’?)
Let’s exclude food wastes. I’m talking about a paper bag, a candy bar wrapper, etc.
It used to, but in general (American) usage, it has recently come to mean anything we wish to dispose of. The distinction seems to have begun fading away when cities and towns stopped having separate trash and garbage pickups. You’d probably be hard pressed to find a Gen X’er who is even aware there ever was a difference.
In that case, technically, yes. Mangetout’s point about modern landfills being anaerobic is correct. That’s why they now commonly cap them off, landscape over them, and turn them into parks, when they’re full. There is little danger that the hills will subside into a pile of goo, because no noticeable decomposition is taking place.
Whereas, if you toss your paper bag out the window, it will eventually decompose. Of course, in the meantime, it will look like hell. And, that candy wrapper is plastic. I don’t believe they’re using degradeable plastics for those, yet. So, it’s permanent, no matter where you put it.
In that case, technically, yes. Mangetout’s point about modern landfills being anaerobic is correct. That’s why they now commonly cap them off, landscape over them, and turn them into parks, when they’re full. There is little danger that the hills will subside into a pile of goo, because no noticeable decomposition is taking place.
Whereas, if you toss your paper bag out the window, it will eventually decompose. Of course, in the meantime, it will look like hell. And, that candy wrapper is plastic. I don’t believe they’re using degradeable plastics for those, yet. So, it’s permanent, no matter where you put it.
The garbage garbage term you are looking for Mangetout is putrescible waste. As opposed to trash like paper etc. 
I don’t think plastic exposed to the Sun is permanent. The UV breaks down the bonds in the plastic. I have a glass-top patio table with a hole in the center for an umbrella, and it came with a plastic ring to line the hole. That turned yellow, and brittle, and broke, in about a year.
I think the real environmental impact of all the trash and garbage is in its creation, more than its disposal. Recycling, reusing, and never creating in the first place are better than either way of disposal.
I suppose the argument could be made that landfills sequester carbon, wheras throwing garbage out the window puts it back into the environment. Not sure how significant this would be, however.
My memory is extremely hazy, but from a National Geography journal sometime in the 80’s, they did an ‘excavation’ on the NYC dump and found newspapers that was still readable and whole heads of lettuce out of it.
In theory, I suppose the best way would be to chuck everything into a composter and hope for the best.
I sure didn’t.
Don’t tell me that tossing trash out of the window is better for the environment than disposing of it properly. Next you’ll be trying to tell me that Iron Eyes Cody wasn’t really an Indian!
You could imagine that if few enough people existed, then the waste they produce could be composted. The waste would turn into dirt quickly enough to keep disease, vermin, etc. from being a problem.
There are so many of us creating waste now that we must do something else. I liken it to the sewage treatement plant: If you are a small group of people, your toilet pit or what-have-you will not be large enough to create an environmental problem. Since our population centers are large, we must “hurry up” nature’s process via the sewage treatement plant.
I hope nobody’s reading this at breakfast ! 
There’s an interesting book about this subject: Rubbish: The Archaelogy of Garbage, by William Rathje and Cullen Murphy. The book is ten years old now (my, time does fly!), but it’s still very current.
To sum up (as Inigo said):
There is usually some decomposition going on in landfills, but not much, and what decompostion does go on is usually anaerobic, which means the end product is methane not carbon dioxide.
Better for the environment? Well, generally the problems with landfills leaking is not biodegradeable stuff, but heavy metals and other nasty things. And while indeed they are to some degree limiting global warming by keeping carbon locked away, the methane produced by the limited decompostion is much worse than carbon dioxide, so they’re probably not much of a net gain if any. There is benefit in reducing the volume of trash – you don’t need to build a new landfill as soon, burn less gasoline hauling it around, and so forth, so that’s probably the best reason for not landfilling stuff.
Probably the best solution environmentally is to put as much as possible into a composting facility and use the result as fertilizer instead of a petrochemical-based fertilizer. That would be a big net environmental gain.
Of course, just tossing garbage isn’t quite as beneficial. Aside from esthetic problems, there could be health problems as well.
You can also incinerate trash – not without environmental drawbacks, as everyone knows, but the benefits may outweigh the costs in some circumstances.
(By the way, Quercus, I like your name. One of my favorite tree types.)
A) There are many, many different types of plastic. Some ARE susceptible to UV. Some aren’t.
B) Candy wrappers are often mylar, which isn’t UV susceptible.
C) Even susceptible types don’t BIOdegrade, which is the key. They may break down into little particles, but they never reenter the ecosystem. There are some mutant bacterial strains that can devour plastics, in the lab, but we don’t want those getting loose and wreaking havoc on our “plastic fantastic” lifestyles. Even then, I don’t believe the byproducts of this decomposition is usable by any other organism.