I've akshully done some work with the premier researcher in the field of garbology (Bill Rathje by name, professor at U of Arizona). He has taken core samples of solid waste landfills, using an enormous coring tool to take samples about 5 feet across down to depths of 90-100 feet. He has pulled up completely intact heads of lettuce that were in the same layer as newspapers from the 50's and 60's - so the landfill had preserved something as fragile and prone to decay (at least in my fridge) as a head of lettuce for decades!

A very brief piece with some of the surprising results of this is here: http://www.acnatsci.org/erd/ea/landfills.html