How likely are you to get organics and metals out of a 300 million year old peat bog? It’s not like there’s a largely organic mineral that contains higher than normal concentrations of mercury due to the bioaccumulation of that element in prehistoric marsh… oh wait…
I wasn’t suggesting they would find fossilized trash, I was thinking more along the lines of what sedimentary rock that formed from a landfill might look like. I’m not a geologist so obviously this isn’t worth much, but I was picturing a mineral high in organics (kerogen?) and rich in Cu, Fe, Mg, Al etc. that might be unique. Landfills are pretty much the largest structures we’ve built so I figured if anything would be found, they’d be it. Although I accept your point about the likelihood of future geologists attributing anything they find to an ancient civilization.
It seems the lunar erosion rate from solar wind sputtering is believed to be ~.003 Angstroms/yr
[ Kerridge JF 1991 PROCEEDINGS OF LUNAR AND PLANETARY SCIENCE 21:301-306], which would lead to the erosion of about 20 um over a period of 50 million years. I don’t know if a metallic spacecraft would be more or less susceptible to this erosion than the lunar surface, but I’ll assume it’s the same order of magnitude and conclude that this type of weathering isn’t a problem.
The long-term lunar erosion rate due to all sources is estimated to have averaged ~ 2 mm/10^-7 yr over the past 3 billion years or so [erode.evsc.virginia.edu/papers/craddock&howard_lunar.pdf]. This gives us the erosion of about 1 cm of lunar surface over the period of 50 million years - it would actually be a bit lower since impacts have decreased in frequency over time. This is the average over the entire lunar surface, so there would be local differences that might be much more or much less than this. Since we have 6 Apollo descent stages, 2 lunar rovers, and a dozen or so other probes on the moon, it’s not unreasonable that one might luck out and survive a geologically significant time period. Granted it would be easy to overlook, but if the civilization surveyed the moon at sub-meter resolution it’s feasible they could find something.
Consider some herding cultures today, or even semi sedentary ones like the vikings. We have remarkably little left of them even after only a thousand years. They worked metal, built and sailed ships, made beautiful clothing weapons and jewelry, and yet we don’t have loads and loads of the stuff to study. A dinosaurian culture may not have had much need of technology to flourish to high level of cultural complexity. Perhaps they had little need of shelter, and were highly nomadic. Considering many had plumage, they might not have much need of decorative objects, but probably would have created art from natural materials. If they were carnivores or meat heavy omnivores they wouldn’t have invented agriculture and would not have built complex stone cities. Container culture might have emerged and animal husbandry was a probability as well. Despite all the complexity you probably wouldn’t find much if anything from such a culture so many millions of years in the future. It would astronomically small odds to find a fossil showing something like that.
Not really. Fossilization is the exception, not the rule. We find dinosaur bones because there were so many of them, living across a span of millions of years.
While there are a lot of humans, we haven’t been around very long. Our civilization really is about five thousand years old. Our modern civilization, with its big cities and global imprint is much younger.
We are less than a blip, geologically speaking. The more I think about it, the more I think that if our civilization vanished tomorrow, it would take a very lucky paleontologist to find any trace of it 150 million years hence.
Which sets me to wondering about the cause of the extinction event at the end of the Jurassic. Hmmm…
(The Sleestaks! Those maniacs! They blew it up! Ah damn them! Damn them all to hell!)
CO2 levels are clearly exceptional within the context of the last million years and probably the foreseeable future. On geologic timescales, this is not true, but when you’re in a pine forest a redwood sticks out, even if there are mountains around the forest.
Likely issues: Short time frame. CO2 emissions, in the long view, are inherently limited. Sooner or later we simply won’t be able to afford, either in the production of or the amelioration of the effects of, burning more fossil fuels. Give it a century or so after that, and we’ll promptly plummet back to a more “natural” equilibrium as CO2 is absorbed into the ocean and converted to carbonates. A blip, even a pretty big blip several times the typical range, is going to be hard to catch.
Although this seems insurmountable, there have been questions similar in scope and nature that we’ve solved. See, for instance, the KT-impact event, which was originally hypothesized due to a spike in iridium concentrations, despite a brief elevation period.
Also, we run up against the attribution problem. We have the benefit of knowing that we’re spewing billions of tons of CO2 into the atmosphere, which at least gives us a very strong starting point in attributing it to us. Geologic observers wouldn’t have that advantage–CO2 comes from a lot more places than iridium.
Are there any areas on the planet that are protected from erosion in a more-or-less stable fashion? For example, might there be artifacts buried in the ice of Antarctica? (Edit: just searched for “ice” and realized I missed marshmallow’s post. Was it ever answered?)
Some denuded desert areas (Namib, Australia, Atacama) may be stable on orders of millions of years. Tens or hundreds of millions of years (the OP’s timeframe), not at all. On those long timeframes, you’re talking mega-geological processes dominating. Think plate tectonics, associated orogeny, mega-vulcanism, that kind of thing. Although some current thinking is that the Earth has moved on beyond that last one, but we’ll see…
Im finding this a bit odd. Fossils are just stone and often not necessarily particularly tough stone.
The idea that every single stone object will be gone seems unlikely to me. They might be hard to find or there might be a chance none survive in easily findable spots.
But I think there must be some chance that some would survive, given we’ve basically covered the globe, and are in every habitat. Some of our more recent works might be more fragile, but theres a lot that came before it. Even if they dont survive directly there must also be the chance of equivalent fossilisation occurring, given you’re starting with much more durable objects than bones in the first place. Gems also come to mind, diamonds take billions of years to grow.
Most importantly there are various nuclear products that dont currently occur in nature, or rather only occur in ways consistent with decaying over time. Plutonium 244 has a half life of 80 million years - finding that in any quantities would be surprising given our understanding of its formation, the age would be all wrong. So the natural reactor argument doesnt work for me as a disqualifier.
Theres also the mass extinction we’ve done, there haven’t been too many of those identified of similar levels. Couple that with the rise of particular species, and a bit of wondering might occur?
While no single thing might be a smoking gun, I think there might be a chance of a combination of data being available that would be noticeable.