I think the reasoning behind this is that natural substances are things we are more likely to have evolved in the presence of, and therefore we are more likely to be able to process. This is not always the case, but on the whole, "natural" substances are a safer bet.

This is probably incredibly silly, but the problem with time travel seems, to me, to be the issue of where you will appear. Relative to the sun (not to mention bigger things), the Earth was in a different position years (or minutes) ago. If you traveled back in time wouldn't you emerge into empty space?

I highly recommend episode 3 of the 1980 television Cosmos. This episode made Copernicus my hero.

I agree. Long term thinking and short term thinking both have their advantages and disadvantages. The bribe scheme would seem to skew matters in favor of the short-sighted (and incidentally cheaters as well).

what about star trek uniforms?

Funny, I thought this was a continuation of an earlier thread and that Cynical Slashdot nerd had misspelled "feces".

Like below sea-level?

I think what you saw are called galls. I saw this in the Attenborough documentary series "Life in the Undergrowth".