system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do we know that plastic takes 450 years to break down in the environment if we haven't lived so long to test it?
gpt
Extrapolation. We look at a piece of plastic at X time intervals and take measurements, then apply that information to what we know about how things decay (Surface area vs volume, etc). The combination of the two gives us an approximation. It might not be 450 years, it might be 200 or 900. The point is more about the time scale over which the material will break down. Meaning that it's not going to just be a month or two like organic waste, but also not tens of thousands of years like radioactive waste. 

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