Plausibility of Materials Lasting Millions of Years

Question

I've seen a lot of articles and even questions here which talk about how long modern human artifacts will last. Mostly it seems to boil down to modern materials not having great longevity, though stone has lasted thousands of years. I gather metal doesn't tend to last because it tends to react and corrode. What I'm wondering is this.

Without invoking handwavium super materials, it is plausible within known chemistry to engineer materials that could last for many millions of years? Could some synthetic form of stone resist weathering for extreme periods of time? Could some metal alloy? Would being buried under ground held or hinder this? Space and vacuum probably make this easy, no? Obviously we don't yet know of such things, so there is no specific material to be pointed to, but is the possibility plausible?

I don't mind leaving the material vague, but I'd feel better about it if I knew it wasn't completely nonsensical. I'm working on really old alien artifacts and ruins and am trying to gauge what could still be around and where, 60+ million years later.

Edit: Noticing a couple calls for clarification.

In the setting I'm working on, a bunch of aliens got wiped out over 60 millions ago. There might be some intact stuff here and there capable of maintaining itself, but mostly I'm wondering how feasible it is for them to have built tools, buildings, vehicles, etc out of materials that could survive to the present day. Buried, underwater, or out in the open, without having to invoke unobtanium/handwavium materials.

Is it plausible that a material based on chemical matter can be that durable?

Answer 1

TL:DR Absolutely, not even an issue. There will undoubtedly be artifacts that are discernible from this alien civilization, after just a short period of time of only 60 million years. However, it depends on whether you want them to functionally survive, or just survive so that they are discernible.

In pure cosmological terms, 60 million years is just a drop in the bucket.

The oldest dated rocks formed on Earth, as an aggregate of minerals that have not been subsequently broken down by erosion or melted, are more than 4 billion years old, formed during the Hadean Eon of Earth's geological history. Meteorites that were formed in other solar systems can pre-date the Earth. Particles from the Murchison meteorite were dated in January 2020 to be 7 billion years old.2

As another poster in another answer has stated, the fossil record on Earth goes back at least that far. See this, for instance.

Sixty-six million years ago, the asteroid that wiped out the dinosaurs also ushered in the age of the mammals – an age that continues to this day.

Scientists have known little about the mammals that survived and flourished in the years after the asteroid impact. Until now.

A study on a recent discovery of thousands of mammal fossils at a nature preserve near Colorado Springs, Colorado, has shed light on the little-understood era.

So if archeologists on Earth can deduce what happened on Earth 60 million years ago, it is well within conjecture that remnants of a 60 million year old civilization could remain somewhere in the galaxy.

Based on the success of our archeologists today, here on Earth, we can say with some confidence:

If their function were purely decorative, they could still be discernible and their decorative nature appreciated.

If they were unmechanically functional (like a hammer, with no moving parts) their use would certainly still be discernible, and maybe even functional.

If they were mechanically functional (like a wheel and axle, a simple machine, or even gears and cogs) their function could be discernible, but they would probably not be functional.

If they depended on conducted energy, such as electricity, they would probably be a complete mess, undiscernible. Our electronics have a life much less than even 100 years, before the circuitry degenerates due to molecular and atomic drift. Passing electricity through a material causes all kinds of changes at the atomic level. However, advances in carbon nanotube technology suggests that with continued development, 'electronic' devices could be made from carbon nanotubes that might be discernible, but probably not functional, after that long. We simply do not know yet how stable we can make carbon nanotubes. After all, diamonds, that will last billions of years, are also made from carbon, in a matrix/lattice structure. If carbon nanotubes can be made even close to this stability, 60 million years is but a blink of the eye. It might depend on whether they are used, or dormant, for that length of time. Dormant devices may not degrade, as there is no conducted energy going through them. The problem with our electronics today, is that there is so much use of chemicals and substances that eventually dry out (insulation, heat transfer goo, and dielectrics in capacitors and transformers for instance). Our electronics will probably be discernible in a hundred years (if they are not recycled) but I doubt if they will be functional. Even electrical motors will be iffy after two hundred years of use.

Materials such as glass and diamonds will be around for billions of years. So if a diamond were engineered, for instance it was cut or engraved, it would be essentially intact. Decorative and functional objects and artifacts made from glass would also be intact and functional, after only such a short time.

A mathematical model shows it would take longer than the universe has existed for room temperature cathedral glass to rearrange itself to appear melted.

So yes, even after the demise of human civilization, after 60 million years there will still be evidence of our former existence from our artifacts that have survived. It will be much like archeologists sifting through the fossil record of Earth, going back some 60 million years ago, trying to decipher what we were all about, but our existence would certainly be evident.

However, functionality will be a completely different issue. But the question does not seem to require functionality, only discernibility.

Answer 2

Fossils

We have many, many artifacts that are millions of years old. We have examples of teeth, bones, amber, and shells that are tens or hundreds of millions of years old. If you're just looking for evidence they existed, we have fossil impressions of dinosaur footprints where they happened to walk through mud that was subsequently buried.

As far as constructed artifacts go, the oldest stone tools we've found are about 3.3 million years old, about a million years older than the earliest Homo species.

Make something out of dense, water-resistant materials like stone and bury it in compacted clays or silt, and it can last millions of years if left undisturbed.

As a specific example, if they hadn't largely been excavated in the 18-20th centuries (and assuming they survived any further volcanic eruptions), I'd expect that the burial of Pompeii and Herculaneum by the eruption of Mt. Vesuvius could have resulted in a wealth of Roman-era fossils preserved under all the ash.

Answer 3

This would give a different spin, but you could go for a machine that repairs itself. Say it only needs a handful of basic materials that are available in its vincinity. The machine would not have general intelligence, just enough to maintain itself and the messages it holds in some form.

Answer 4

This is currently being developed by the University of Southampton. The technology is called 5D optical data storage. I am no expert in this technology but the researchers claim that it can store information for billions of years:

The memory crystal is capable of storing up to 360 terabytes worth of data for billions of years. The concept was experimentally demonstrated in 2013.

The technology is being developed by Hitachi and Microsoft.

Answer 5

It depends the material. At time spans of millions of years, half lives of common elements can become important and this is a nuclear reaction, not a chemical or mechanical one and so progresses even if the material is otherwise chemically protected or non-reactive and mechanically protected.

This is part of the reason you can't just freeze a person in cryostasis indefinitely even if it somehow stops aging 100% because without biological functions and nutrients to cycle through and repair the body, the elements that constitute the body decay into other elements over a long enough period of time. The more something relies on things being exactly the element it is supposed to be, the more sensitive it will be to these changes.