Comment by simonh | Hacker News Reader

Comment by simonh | Hacker News Reader

It’s true that only very few individuals would be fossilised and fewer if they found. Nevertheless we do generally find multiple fossils of the same or closely related species. We also find fossils of multiple stages in the evolution of many species. So it seems unlikely to me that we would find zero fossils of a species advanced enough to colonise the entire planet, as we have, nor any of their ancestral species.

It also seems likely that technological artefacts would leave fossil-like impressions, or for mineral objects like ceramics simply straight up survive in strata. Such artefacts would massively exceed the number of individuals and trash has a tendency to get widely distributed so it seems extremely unlikely none would be found.

One idea is that they might have only lived in a small geographic region such as an island, and if that location happened to subduct and not reach the surface we’d never find them. Well yes, but the major advantage of technology is that it allows you to overcome geographic and climatic barriers, which is why us hairless tropical plains apes have colonised every region on the planet, and did so everywhere except Antarctica but including the arctic with Stone Age technology. An industrial society would also create demand for resources, prompting global expansion.

So it’s an interesting thought experiment, but I just don’t see how the hypothesis is really viable. Not impossible perhaps, but extremely low likelihood to the point of implausibility IMHO.

I do agree that a society capable of nuclear power or space travel can be considered implausible. A similar thought experiment might be, "how technological could a prior species have become before we'd notice?"

Animals today, from dolphins to chimps, can be found using tools. Is there any reason to believe this didn't happen in the age of the dinosaurs? Then you can expand beyond simple sticks and stones to other primitive technologies. Maybe we weren't the first to figure out fire, or agriculture, or animal husbandry.

Or maybe any brain capable of fire + agriculture + animal husbandry will eventually be so successful that nuclear power and space travel are inevitable.

I'm not arguing in favor of any of this: it's just fun to think about.

In my will, I'm going to ask that I be buried in soft mud in a river delta, or some similar place likely to become sedimentary rock in the far future. But I also want to be buried with some relic that proves I was a member of a technically literate civilization. I surmise something like a wooden abacus. The wooden abacus would fossilize along with my remains. I hope my fossil, and the fossilized object I carry, will be found in the far future.

Cynically, with how much trash there is around rivers you're likely to be fossilized within a strata chock full of traces of our civilization.

Non-cynically, I would recommend having a stone abacus crafted if you wish to be buried this way - effectively mineralize the relic manually and don't leave its fossilization up to chance. You could also try encasing some objects into amber or resin and scattering them around your final resting place.

The distribution of fossils between continents was one of the pieces of evidence used to support the hypothesis of continental drift and plate tectonics. It would make sense that any prior civilization would also be introducing species outside of their native ranges, or making several species show up in disparate parts of the globe with no good natural explanation. https://en.wikipedia.org/wiki/Columbian_exchange versus https://en.wikipedia.org/wiki/Great_American_Interchange

This species is particularly fascinating because it is only found in Japan and parts of Texas. No one has a good explanation for why, although no one is suggesting an ancient civilization did it.

https://en.wikipedia.org/wiki/Chorioactis

A fun thought experiment is to imagine what we will do once we leave the cradle of Earth behind. Will we just leave all of our junk here? Make the homeworld a monument to our past? We would know that it wouldn't last, everything decays with time so some would argue it would be a crime not to preserve it and the only way you can be sure to preserve something is by regularly tending to it. I imagine many would argue that we take all of the most valuable artefacts with us, keeping them in pristine condition and on display. This sentiment might even extend to our dead, why leave them to be ground to dust by the uncaring aeons? Inter them in gigantic space crypts instead. Further, we may be determined to leave a pristine planet behind for the animals that still reside there and, eventually, for the next species to crawl its way up to sentience. Jeff Bezos has expressed a wish similar to this for our future. Move everything into space and keep the Earth as a giant nature reserve. Hundreds of years from now perhaps we will do that and after that maybe we will even leave the solar system behind us as we strike out into the universe. Now cast your mind back tens of millions of years and imagine some other intelligent species doing the same for us.

> A fun thought experiment is to imagine what we will do once we leave the cradle of Earth behind. Will we just leave all of our junk here? Make the homeworld a monument to our past?

It is a fun thought experiment, but humanity is big. Humanity leaving Earth would be extremely more likely to look like a few people hopping on a ship and flying away and everything else stays the same.

For it to look anything like "last one out, turn off the lights" type of thing, energy would have to be truly free and there would need to be a _very_ compelling evacuation scenario. Otherwise there would be a lot of people left behind for social/economic reasons or because they just don't want to leave.

It's all about incentives. A huge percentage of the human population has decided to live in cities because they offer a variety of incentives to live there. The transformation isn't complete but if the benefits were even greater then you could eventually see a complete shift.

Who knows what incentives a hyper-advanced civilization might have? Maybe life in space is a million times more appealing than life on a planet for a sufficiently advanced technology level. If estimates are to be believed then the resource wealth of the solar system far exceeds anything contained within the Earth. If you've solved the problems of efficient space propulsion, resource extraction and construction then you would have access to an abundance of everything you need. Space also has a lot more space, enough room for any person or group of people to build whatever they want without annoying their neighbours. It also has more energy both in the form of sunlight and radioactive elements. So yes, maybe energy and matter are nearly free for a true space faring civilization and maybe that's the reason no one would want to stay behind or at least so few that they would leave very little evidence of their presence.

So this article: https://www.science.org/content/article/most-species-disappe...

says that of modern threatened-but-not-extinct mammal species, we have recorded fossils for 9% of them. For non-threatened extant mammal species, we have recorded fossils for 20% of them. Assuming that's correct, it doesn't seem crazy to imagine that we might not have fossils for a species or it's say 5 ancestors species that existed let's say 10M years ago -- fossils are also subject to being broken or subducted and so we would expect recent species to leave a greater fossil record. And being an intelligent, cultural species may reduce the chance of fossils being formed for high populations, due to death practices.

We do find for example many different fossils for say triceratops. But that shouldn't be taken to mean that we find lots of different fossils for every, or even most, species extant at the time of the triceratops.

Considering an extant species is like picking an arbitrary point in the existence of a past species, and excluding all fossils formed after that point. On average that half the fossils. As for threatened species, just a guess, but I’d expect most of those to be likely have relatively small populations to start with and live in constrained habitats, all factors that would tend to mean they would leave a lot fewer fossils on average anyway.

A advanced technological species would need to exist in huge numbers to support a developed economy. Id expect them to colonise widely. Also I’d expect artefacts to exceed individuals by probably a handful of orders of magnitude.

I think you're dramatically overestimating the likelihood that artifacts would survive in recognizable form for millions of years. I do think we can be reasonably sure that there was no advanced technological society let's say 50,000 years ago. But 20M years ago is another story. 5M years might be another story.

Whether you'd find fossils of an advanced technological species at a point in their history when they might have a population of billions seems incredibly contingent on unknowable things about their culture. But the question of whether you'd find fossils of them from their prehistoric period (in which their population would not necessarily be enormous), or of their evolutionary ancestors seems less contingent, and very plausibly you wouldn't.

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