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Comment by imglorp | Hacker News Reader

Has anyone methodically looked for artificial materials like microplastics in the geological strata?

Yes, in that people try and identify what’s there. No, in that it’s not expected to find evidence of a prior advanced civilization. The prior existence of oil as an easily recoverable resource is a strong indicator that nothing like our civilization existed in the last several million years.

That's true about the oil; coal too. If we're not completely wrong about how those resources are created (there are some alternate theories) then we're the first civilization to use them.

However, most of what I've read about prehistoric advanced civilizations discussed them using crystals (quartz) and deriving energy from the earth. Some form of piezoelectricity. There are theories today connecting earth quakes, quartz deposits, and ball lightning, which could be hinting at an energy source we haven't explored yet.

We sent humans to space and robots to Mars and other planets, we are extracting energy from nuclear fission, we will likely build an artificial star soon enough. It's extremely unlikely that we could have missed some mysterious quartz power source.

After a couple thousand years of computational evolution, if you don't think there'd be a possible reason for leaving behind massive silicon crystals... Well, you haven't been reading enough science fiction.

If you could grow pure crystals more easily (thinking Diamon Age), why not have giant plates serving as a piezo generator or ambient electromagnetic waveguide harvesters?

So a civilization thousands years more advanced than us failed to go to space (evidenced by the fact that they did not leave behind any space junk) but somehow produced energy from crystals?

FWIW, space junk wouldn't necessarily survive that long. Things on lower orbits would deorbit themselves quickly without station keeping. Things on higher orbit would get pushed away by solar radiation over long time, and degrade under high-energy radiation (such as UV rays). What remains would be hard to find, because space is big, so it would have to be fairly large and/or fairly reflective for us to notice now.

Wouldn’t any constant force tend to ellipticize the orbit and lead to a return to earth?

Would have to do the math to be sure, but doing some quick simulations in my mind - I believe you're correct, modulo the impact of the orientation of that force changing (Earth goes around the Sun). Let me illustrate with a diagram:

                      PROGRADE
                     (raise apo)
                          | 
           +--------------+--------------+
           |                             | 
           |   ->      --->---      ->   |
           +-  ->    -/       \-    ->  -+
               ->   /           \   ->  
             / ->  /    /II\     \  |   -+
       +----+  ->  |   |IIII|    |  |    +- IN SHADOW
       |     \ ->  \    \II/    /   |   -+
       |       ->   \           /   ->
       |   +-  ->    -\       /-    ->  -+
       |   |   ->      ---<---      ->   |
    RADIAL |                             |
     IN    +--------------+--------------+
  (also raise apo)        |
   ((I think...))     RETROGRADE
                     (lower peri)

This shows a body in orbit (the empty sphere) around the body (the filled sphere). The orbit goes clockwise, sun radiation comes from the left, arrows illustrate the acceleration it creates on the body. Simulating it in my head, I believe such setup would lead to the orbit getting elliptical, with the apogee getting larger and the perigee getting smaller, all the way until either the perigee hits the atmosphere or the body reaches escape velocity (thanks to small, but unbalanced contribution labeled RADIAL IN).

I'm not sure how long such a process would take for a satellite not designed to exploit solar radiation for propulsion, nor whether it wouldn't be dwarfed by other orbit-disturbing influences such as the Moon and other planets.

Also: aerobraking a highly elliptical orbit isn't going to leave you much of a satellite to find.

(Note: I studied orbital mechanics in university on Kerbin, under Jebediah Kerman, so I might be wrong here.)

It would only be eclipsed, daily, during a small part of each half-year, no? And, on alternating sides of its orbit.

Usually people blame the moon, and three-body dynamics, for disrupting other Earth orbits.

> evidenced by the fact that they did not leave behind any space junk

Whatever space junk we leave behind will be gone 100 years from now. https://www.nasa.gov/news/debris_faq.html

That’s really not what that means. The 4th satellite Vanguard 1 was put into orbit in 1964 and it’s expected to have a 240-year orbital lifetime despite getting to within 657.3 kilometers of earth. https://en.wikipedia.org/wiki/Vanguard_1

Geosynchronous satellites 35,786 km (22,236 mi) are going to be up there for a very long time.

PS: If you’re interested https://aiaa.kavi.com/apps/group_public/download.php/3172/IS...'

And anything that went to solar orbit will be the more or less for ever, subject only to the slow erosion of thermal cycles over the eons. And all Pioneers, Voyagers and New Horizons will not have to sustain even that, just comic rays.

BTW, it's a bit mind boggling how big and empty even just interplanetary space is - there could be wrecks of an unlucky discovery fleet paying a visit couple milion years ago and we might never find them unless they come really close to Earth or other sensor rich human inhabitted place or possibly still produce some active emissions (outgassing, sporadic radio signals, abnormal heat absorption/radiation, weird albedo variations, etc.).

I think that’s just for lower orbits, I was under the impression our geosynchronous satellites will be up there for millions of years (unless future humanity cleans up the geosynchronous graveyard orbit)

That's all nice and dandy until aggressive aliens wielding muskets show up in wood & brass starship: https://en.wikipedia.org/wiki/The_Road_Not_Taken_(short_stor...

The premise of this story is hilarious and wonderful to contemplate as a possible scenario. Food for thought and thanks for the link. I'd never heard of it before.

There is the hypthecial concept of a https://en.wikipedia.org/wiki/Nuclear_lightbulb which pending some so far unavailable metamaterial would reach temperatures of up to 20,000°C and generate mostly hard UV-light in a closed cycle.

Which reminds me of some decsriptions of Indian Vimanas, or rather the parts about their engines, which allegedly were made of some crystals.

Indeed most of our fossil fuels were created during a window in the evolution of life on Earth where plants had developed tough cell membranes that the microbiota could not deal with and transformed the planet into a massive mountain of underbrush in a heavily oxygenated environment. The forest fires must have been spectacular. Trees grew tall and eventually died. Then they fell over, but did not rot. Instead stacking deeper and deeper. This is why we have seams of fossil fuels in the ground to draw from today.

If we wipe ourselves out the following civilization will have a much tougher time getting through their equivalent of the industrial age, especially if they're dealing with the aftereffects of climate change.

But not finding fossil fuels wouldn't tell you anything, because nobody knows how much there ought to be.

If they discovered better sources of energy a little faster, they would stop pumping almost immediately. But for politics, the US might easily have started the switch to wind power forty years ago, and billions of barrels' worth would still be in the ground.

Oil is useful for a lot more than just burning it. Fertilizers, plastics, and asphalt are the most well known but a host of industrial processes use it as a feedstock. It’s only recently that oil has been hard to find, initially it was seeping up from the ground which still occurs on the sea floor in some areas making it hard to miss.

So some other civilization could exist without using it, but they would look nothing like ours.

It is one thing to use it, entirely another to exhaust it. A civilization consuming only 1% as much could look very similar, if it were not dependent on oil for fuel.

We don't need to exhaust it. We only need to exhaust the easy to find sources.

Oil is overwhelmingly used by burning it and its products. Only 4% of it goes to plastic production.

It’s not just plastic but also Asphalt, Lubricants, Fertilizer, etc. However, let’s assume they only used 10% as much oil as us and only used oil for ~100 years before dying off.

They would still have started with easily extracted sources not offshore oil or ultra deep oil. The world had very easily extracted oil when we started. Further, there is no missing oil based on geology.

Oh, you have checked? There have been no dry wells?

I wonder where the term "dry well" came from.

Most dry wells are around oil fields. We have fairly good understanding about the overall geology of oil fields, but you can have a dry well 50m from an active well. What we don’t have is most expected oil fields without oil.

We know about the KT extinction layer (which contains a lot of iridium, a potentially extremely useful but rare metal) but attribute it to meteorite ejecta. It also coincided with large scale climate and environmental changes. That's the only candidate I know of as a non-geologist.

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