[throw310822]

So we have microbial fossils from 3.5 billion years ago, fossilised 300 million year old skin, bones from almost 200 my ago, even actually soft tissue inside a fossilised bone from 70 my ago. Ah, footprints too, the most unsubstantial matter of all: pure shape. That's in addition to all the million other fossils that are so common we hardly care: shells, small bones, etc.

And someone is saying there could have been an entire advanced civilization 400 million years ago, large and powerful enough to cause climate change, and that no traces of it would possibly be left? Like, billions of individuals, cities, factories, metals, concrete, mines, wells, roads and bridges and tunnels, stone sculptures!, plastic, waste dumps, farms, agricultural land, billions and billions of artifacts of all materials, most of them entirely artificial. All gone because "nothing resists 400 my" and, "oh btw, check this dinosaur footprint and this fossilised piece of skin, how cool"?

[gorgoiler]

The counter argument: dinosaurs were around for a staggering amount of time, no pun intended. 165 million years is reasonably long enough to ensure they left behind some nests, bones, and a feather or two. Modern humans have been around for more like 0.02 million years.

The counter-counter argument is that while we’ve been here for a comparative blink of an eye, we’ve left behind 4 orders of magnitude more stuff than just nests, bones, and a feather or two.

[throw310822]

Indeed. Did a rapid check on T-rex, just as an example. Was around for max 3.6 million years. Max population at any one time must have been around 20k individuals. We have about 150 skeletons.

So current human population is 400 thousand times the maximum T-rex population at any one time. A few decades are enough to produce more human individuals than the entire T-rexes history. We also have the ability to go (and die) pretty much anywhere, so there will be human skeletons in every crevice, depth and environment on Earth. We also produce an absolutely staggering amount of artifacts of all kinds, from plastic straws to giant tunnels and artificial caves. There are zero chances an advanced civilisation on Earth won't be aware of us in 400 million years.

[T-A]

>We also produce an absolutely staggering amount of artifacts of all kinds, from plastic straws to giant tunnels and artificial caves.

Plastic will be gone in ~1000 years,

https://www.activesustainability.com/environment/waste-plane...

tunnels and artificial caves in a few million years at most as they are compressed by the weight of the rocks above them ("tunnel squeezing").

[throw310822]

How long to dissolve carved stone sculptures (in sizes ranging from 1cm to 100m?)

And how long does it take to dissolve skin? Footprints? Because we have those from hundreds of millions of years ago.

[T-A]

> How long to dissolve carved stone sculptures (in sizes ranging from 1cm to 100m?)

A quick search on "rock weathering depth per century" suggests a "typical range" of 0.05 mm to 6 mm, depending on rock type and environmental factors. At 0.05 mm, a stone object with radius 0.5 cm would crumble in 10000 years. With radius 50 m, it would take 100 million years.

I would expect them to be unrecognizable long before that though.

> And how long does it take to dissolve skin? Footprints? Because we have those from hundreds of millions of years ago.

What do those findings tell you about the cognitive abilities and social organization of the creatures who left them behind?

[throw310822]

> A quick search on "rock weathering depth per century"

That's a great illustration of what I meant. Of course an exposed rock consumes away in the space of a few millennia- this is exactly where the "Silurian theory" comes from. Yet it's also obvious that we have plenty of perfectly conserved rocks that are intact after hundreds of millions of years- i.e. fossils. Any small sculpture buried in clay can survive for an eternity.

> What do those findings tell you about the cognitive abilities and social organization

Skin? Like, with clothes on, or the shape of clothes? And shoes and hiking gear? Footprints with the shape of boots? Drawings "I LOVE YOU" in the sand? The shape of a coca-cola bottle buried in solidified clay? Come on...

[nwah1]

Yea, but if humans went extinct tomorrow, very little human artifacts would remain after millions of years. Indeed, most would be gone well before that. How much stuff from the 18th century still remains, in percentage terms?

[bensyverson]

Unless it was burned, melted, decomposed or crushed to dust, it's all out there or in a landfill somewhere.

I do find it difficult to believe that we would not leave enough fossil and mineral evidence for future paleontologists to find. I get that the surface will churn, but layers of rock routinely become exposed, revealing the geological history of the area. No tea cup shards, no impressions of rusted cars in the mud, no concentration of metal in strangely rectilinear formations that suggests skyscrapers?

[neaden]

There would still be many signs. Dug up mines, metal alloys that don't exist in nature along with refined metals in quantities they don't exist, animal and plant species we bred along with all the ones we made extinct.

[nkrisc]

Very few things would in fact remain, you’re correct. But we’ve also created radioactive elements with half lives of many millions of years.

While there would probably very little direct evidence of humans after millions of years, there would probably be at least some anomalous evidence someone could find.

[randomImmigrant]

Actually correct. We have very very few fossils compared to the millions of species that have evolved and gone extinct over 4 billion years.

The fossils we do have are of highly successful species in that geography. It’s a matter of chance, leaving behind a fossil, after all.

And unlike biological matter that can fossilize, industrial structures etc do not. All our manufactured stuff has very short life once it reaches the crust and starts getting compacted.

The more time you add, the better the odds we’d find this evidence lost.

And if this wasn’t a global, but more localized pre-human civilization, the evidence would be thinner still.

Which is why this isn’t a scientific hypothesis really. It’s more showing you the limits of scientific inquiry into the deep history of Earth.

[throw310822]

> It’s more showing you the limits of scientific inquiry into the deep history of Earth.

I think this is it: the point of this argument is to inspire some awe in the listener, making them realise how vast Earth's time is compared to our horizons.

But in practice, the argument is wrong. A dead animal's skin is expected to lasts weeks to months- and yet we have fossilised specimens. A footprint typically lasts hours, and yet we have ones that are hundreds of millions of years old. Even if the expected lifespan of our artifacts is nothing in comparison with these timespans, a small percentage of artifacts will either be preserved or leave recognisable traces- exactly as it happened for soft tissues and footprints. It's extremely naive to think that none of this will leave traces.

[fnord77]

> And someone is saying there could have been an entire advanced civilization 400 million years ago, large and powerful enough to cause climate change, and that no traces of it would possibly be left?

If humanity vanished today, in 1 million years almost all of our artifacts would be gone or burned under miles of subduction.

In 10 million years there would literally be nothing left.

[kergonath]

> If humanity vanished today, in 1 million years almost all of our artifacts would be gone or burned under miles of subduction.

That is completely incorrect. We have sedimentary rocks from 100 M years ago on the Earth’s surface right now, that never underwent any kind of subduction.

[DFHippie]

> under miles of subduction

Subduction only occurs at plate boundaries and is not nearly this fast. Continental plates float on top like foam and do not get subducted. It's the oceanic plate that is created at mid-ocean ridges and gets subducted at the margins.

[throw1234567891]

Bollocks. We find fossils millions of years old right on the surface.