I would guess that glaciers would encapsulate the skyscrapers and dislodge them from their foundation, and when they receded leaving a huge pile of steel and concrete. Even if that was later encapsulated by magma, future geologists would have to wonder about metal 'veins' that were so structured and why part of the rock was basalt and another part was an exceptionally hard and dense form of limestone.
At this point I've sort of lost track of the argument. I read articles about how glaciers preserved soft tissue from the ice age (> 22 kiloyears ago)[1], I've got a bit of rock with a perfectly preserved trilobyte from Montana that is over 380 million years old, and yet people reading want to argue in this thread that massive amounts of inorganic structures built by humans to last for centuries will somehow be dissolved/eroded beyond detection in some short period of time.
So it seems unequivocal to me that human impact on the planet will be preserved for millions of years via the same mechanisms that have preserved snapshots of what was going on millions of years ago.
I don't think so, meteoric iron (according to the wonderful blog series[1]) is early Egyptian.
Iron (and steel) is stable outside the presence of oxygen and water. It doesn't just dissolve. And certainly if it were part of the steel reinforcement inside concrete in a building where special measures had been taken to insure that neither oxygen nor water would come in contact with it (as modern skyscrapers do) would persist for an exceptionally long time.
If there are two things the glaciers you mentioned a few posts back would accomplish it would be creating cracks that would expose things to water and oxygen, and also expose the resulting heaps to loads and loads of water. This is how stones found in glacial deposits look like: https://sv.wikipedia.org/wiki/Rullstens%C3%A5s#/media/Fil:Ru...
Note how rounded all the stones are. And the stones that are there are generally speaking a LOT more resilient than any variant of limestone will ever be (including concrete).
What about when the skyscraper’s pieces are submerged under saltwater for a million years? Or are covered up by a mile of river sediment and then plunged another 5 miles under the earth for several million years?
Or the concrete develops cracks, allowing water into the steel reinforcement, which expands, further cracking the concrete until it collapses. Like modern bridges.
