Comment Re:One non-disturbing theory (Score 4, Interesting) 304
...given that the bottled water aisle of my grocery store strongly suggests that water is a little less ultimate than you imply.
Funny you should mention that, because the reason most bottled water has an expiration date isn't that water goes bad, but because the plastics' volatile components in the bottle leach into the water (which is why everyone freaked out over BPE's awhile back).
Another theory? stuff clings to the plastic and sinks it. Having lived on the Oregon coast, I found it rather rare that something would wash up on the shore which didn't carry barnacles, seaweed, algae, and other stuff that clung to it - all of it using the bit of flotsam as a miniature base of operations from which to spend one's lifespan. Eventually so much stuff clings to it that any buoyancy the plastic once had is negated by the weight of the lifeforms and suchlike clinging to it.
Hell, even a sealed glass bottle eventually does this, as algae sticks to outside of it, which in turn attracts sand... the stuff dries like glue, BTW.
One other reason I can think of, speaking of which - did they account for all the stuff that eventually washes up on shore somewhere? I suspect they had to have, but maybe they underestimated it?