Well, no. Some common plastics like polycarbonate aren't biodegradable, and will basically never break down without application of significant heat/water/enzyma

Well, no. Some common plastics like polycarbonate aren't biodegradable, and will basically never break down without application of significant heat/water/enzymatic activity/etc. For some of these, the half-life could be a great deal more even than 10s of millenia: https://pubs.acs.org/doi/10.1021/acssuschemeng.9b06635#:~:text=Using%20a%20mean%20SSDR%20for,to%201200%20years%20(pipes) https://pubs.acs.org/doi/10.1021/acssuschemeng.9b06635#:~:te....