In addition to nuclear waste, there are other very long lived forms of human detritus accumulating in the world. Most pervasive among those may be plastics. Virtually non-existent before the Second World War, they are now produced in staggering quantities. So far, none of those artificial polymers have broken down chemically; instead, they just break into smaller and smaller pieces, float down rivers to the sea, and end up in places like the North Pacific Gyre. It is also discussed on MetaFilter.
As with vulcanized rubber, these materials will endure in the world until microorganisms evolve the ability to metabolize them. Apparently, when plants first evolved lignin and cellulose, bacteria were unable to digest them. Until that changed, wood would have been as enduring as the plastic wrap currently swirling and collecting persistent organic pollutants in the world’s oceanic gyres, quite probably for millions of years.