The Great Pyramids are 4500 years old (at least). Petra is about 2000 years old.
What is the largest post-industrial man-made structure, that currently exists, that will remain standing the longest?
For the purposes of this question, the definition of “structure” is extremely broad, as well as how intact it must be to be considered “remaining standing”; there should be enough of it remaining that it would still be instantly recognizable for what it was to a person living today.
Judging on the really old structures we still have that are mentioned above, I’m thinking something like Mount Rushmore or the Hoover Dam.
How about Voyager 1. It is expected to reach the Oort cloud in 300 years and pass through in in about 30,000 years. After 40,000 years it will pas within about 1.6 light years of the star Gliese 445. It is not expected to collide with anything and the “erosion” by dust in space should be minimal.
I can’t recall nor find out if it’s heading out of the galaxy, I would assume it could still be recognizable after a billion years.
Kinda stretches the definition of “structure” a bit. Plus, I think the original plan was to carve even more of the figures but they had to curtail things when fissures were found in the rock, so it may be less stable than we think.
Rather than Hoover Dam, I wonder if Grand Coulee or Three Gorges might last longer. Hoover is very tall, and with a lot of pressure behind it. If, and when, the water was to find its way through, seems like the pressure would start to break it up. Grand Coulee Dam is long and low, and without the high rock walls. If the river cut a new channel around the dam, natural erosion would take a long time to wear down that much concrete.
The Vietnam Memorial will get covered up, but once it’s dug out, wont it be still be legible after a thousand years? Or is DC too swampy? Wait, ignore that about legibility, not one of the parameters. I think it will remain as a massive granite V wall for thousands of years.
Still trying to find the cite, but when Gutzon Borglum was asked about Mount Rushmore, he said he added a foot to Washington’s nose. Borglum said he did that after finding out that the Rushmore granite only weathers at a rate of one inch per 100,000 years. He wanted to give Washington another million years.
If it is ever finished the Crazy Horse Monument will be larger than Mt. Rushmore.
What about canals? How long would it take for the Suez to silt up so that water no longer flowed through? I assume there are strip mines larger than Mt. Rushmore, they may not be artistic but like Rushmore the man-made part is simply removal of material that was already there.
Road-beds. (Okay, they aren’t “standing” really. But they will remain detectable for an awful long time!)
Here’s another bad answer: temple pillars in neo-Roman style, at least the bottom two or three drums. It’s a bad answer because only parts will remain standing, and they aren’t really post-Industrial structures, as they pretty much use the same techniques the Romans did…
Have I picked at the edges of the rules enough? (It’s a common sport here!)
Serious answer: a set of concrete storage buildings…somewhere. Maybe a “U-Stor” in Baltimore, or in Duluth, or in Brisbane… But a row of concrete storage blocks. There’s hundreds of thousands of 'em, and they’re just about as solid as can be, while also fairly minimal. They aren’t complicated enough to fail in any fancy way.
In the same spirit as Voyager there is LAGEOS-1 which is predicted to re-enter the atmosphere in 8.4 million years and contains a plaque designed by Carl Sagan.
Are you looking for the oldest structure or the largest structure? It’s unlikely that they’ll be the same thing. If you want some of both, what’s the weighting between the two? What’s worth more, lasting for an extra thousand years or being a half million square feet larger?
If you weigh very heavily towards size, and define size as the largest usable space, then the Boeing Everett Factory is the correct answer. Anything else depends on different assumptions and speculation. Probably closer to what you actually want to know too.
Considering the state of some roads I drive over daily, that were paved less than 10 years ago, a road might not out-last much of anything after a few hundred years.
Wouldn’t cracks eventually form in weak areas, such as the corners of the mouths and eyes, thanks to freezing/thawing cycles, eventually causing the visages to crumble, a la New Hampshire’s Old Man in the Mountain?
I’m looking for a large man-made structure that’s going to remain in an easily recognizable state for a longer time than anything else that was built within a time period of ≈150-200 years ago to the present. The question is purposely vague.