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Let's have fun offering what-have-you questions for Fermi estimates! If we are here for fun, at least partially, let's save some in quantifiable form. Here's mine:
Would a standard piece of soap (neutral pH, lens-like shape) sink to the bottom of the Mariana Trench, or will it get dissolved on the way down?
The soap keeps more or less constant density as it sinks, but the water is denser the deeper you go. And the density of soap is really close to that of water, so I expect that there is some depth at which the soap has the same density as the water, and when it gets to that level it stays there. And eventually it dissolves or gets eaten.