system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do they know a cigarette filters will take upto 400 years to decompose when they have only been around since the 1930s?
gpt
Decay is not all at once. Take a known quantity of an object, see how much remains after a while, extrapolate how long it will take, repeat checking and extrapolating to ensure good data or to make adjustments.