After how long do we stop to let the deceased Rest In Peace?

Actually, “active” cemeteries are often disturbed for one reason or another. Storms – floods and mudslides most often – frequently wreck cemeteries and graves have to be relocated. Or cities change and the land is needed for a building project, in which case an entire cemetery might be moved.

As for me, when I’m done with my body it can go to a landfill for all I care. And my own parents were cremated and their ashes blown to the wind, which seems entirely fitting to me.

If we treated all of the Earth as consecrated because someone had once died or been buried there, we’d never take a step. I think that kind of reverence for garbage – which is what a corpse becomes pretty soon after the animating force leaves it – is perverted.

As far as I know, “rest in peace” referred to the souls of the deceased, not the actual body.

I do have a measure of respect for a grave-site. I would never allow the corpse of someone I loved to be tossed into a landfill. Call it what you will, I think it’s just disrespectful to treat even someone’s dead physical body in such a manner.

What @Nullo said. I don’t think that particular thing has much to do with physical remains.

Still, what an interesting question! If we leave out the “rest in peace” bit, it’s still interesting to ponder why we’re ok with old remains being “disturbed”, but the thought of newer bodies being dug up makes us (at least some of us) uncomfortable. I have no idea what the answer is, but I love that you thought to ask about it.

Most times, when old burial sites are disturbed, it’s as said in the details, archeological study. We dig up mummies and stuff, and we learn about our own history by doing this. Whether it’s good or bad on a specific moral point, it’s probably easy not to feel bad about about passed civilizations that we’re not directly connected to.
Although it’s not unheard of to move modern cemeteries in order to build a mall…but yeah, I guess it’s ’‘okay’’ if it’s in the name of both science and history, maybe?

As for an example like the airplane one…well, people would retrieve the bodies from the ocean if possible. Maybe to give them a proper burial, actually. Lotsa people wouldn’t be okay with the idea of their dead loved ones just left at sea. They might also have hazard laws about that…what if there’s some town near by, the people there might not like having a buncha corpses wash up on the shore lol.

There might be limits, and they may and or may not have valid reasons.

In Europe (Italy, at least), it’s common to exhume all of the bodies in the cemetery every so many decades and re-inter them in a common grave. The reasoning is that there isn’t enough space to bury everybody individually and all the relevant people would have died themselves by then anyway.

Actually, I think that’s fairly common practice in a lot of space-conscious American cemeteries, too.