It takes a very long time....hundreds of years.
According to the February issue of Oprah magazine : It takes a brown paper bag 1 to 5 months to biodegrade; cigarette butts and filters take 12 years; plastic bags, caps and lids take decades;...
500 years.
100 years so none of the plastic ever made has decomposed yet
Brian Eno on the Long Now Foundation
How to Plan for Long Term Care
How to Use Long Gun Optics
How to Use Long Guns in Confined Spaces