1. Genetically modify as many wild plants and animals as we can to have a message encoded in their DNA, and release them back into the wild.
2. In areas that we expect to be geologically not much changed over the next 50 million years arrange concentrations of long lived radioactive materials in patterns that are obviously not natural. Encode a message in those patterns.
3. We could probably do something on the moon with nuclear weapons that could make a long fairly straight trench or series of parallel trenches that would be visible in telescopes and either be obviously non-natural or at least interesting enough to get them to go take a look.
Leave millions of metal spheres, cubes, tetrahedrons, octahedrons, dodecahedrons, and icosahedrons there which contain messages inside.
Google is telling me that any given spot on the moon gets hit be a meteoroid of ping pong ball size or greater about every 1000 years, so many of the messages will likely be destroyed over 50 million years, but maybe enough will make it.
BTW, is meteoroid the correct term? That's what Google's summary used and according to the dictionary definition as a small body that would become a meteor if it entered the Earth's atmosphere it would be correct but when we are talking about impacts on other planets or moons I'm not sure we should restrict meteor and meteorite to just meteoroids that are in or have hit after passing through Earth's atmosphere, respectively.
Anyone deciding to write scifi based on this, try to involve Romans somehow: https://en.wikipedia.org/wiki/Roman_dodecahedron
We should have seen signs of similar non-uniform usage in the strata from before that time period. I wonder if any research has been done on this.
And all the byproducts of this use. We are leaving abundant traces of our existence basically everywhere. We can see it in the ground, in the seas, in the ice caps. Our existence will be very obvious to anything caring to just dig for quite a long time.
For example, we don't have any ice core data older than ~5 million years. (Much lower, if you limit it to continuous spans.)
Maybe some rings?
At all? Like nothing that would be observable 50M years later?
Think about something you believe would last 50 million years. I am sure someone will be able to point out how and why that would just disappear after such ridiculous amount of time.
Or you could try leaving particular "signatures" of radioactive elements. Not ones with a short half-life, obviously, but xenon-124 lasts pretty long, tellurium-128 will survive anything except the heat death of the universe, and there's a few others like that.
> a civilization like this would not leave a trace on the geological record
Am curious: if dinosaurs can be found with intact skin [1], after 110 million years, why not remains of the civilization's "people" (bones etc.) after 60-50 million years?
Or maybe we _did__ find their remains and just have no idea they were part of an intelligent civilization. I mean, that's not a question any respectable researcher would be inclined to raise in the paper about the discovery...
Wrong timescale though. 10000 years vs. 50 million. Millions of years is a very very very long time, our intuition is often wrong about timescales like that. For example a lot of modern land was still molten rock underground and vice versa.
The problem I see is they either had to use sustainable hydrocarbons (so, carbon-neutral) or they would have used up the fossil fuels we're currently using.
Would they have been using the same deposits we are suing, or would new deposits have formed over the last 60 million years?
Or could they have depleted their own, but what was un-usable 60 million years ago, have become usable today. Like something that was marsh land 60 million years ago, be coal today?
For those unaware, the PETM was a rapid increasing in global temperature (and CO2 concentrations) around between 60-50 million years ago. This lead to a minor (on a geological time scale, major for those creatures living through it) climate crisis.
The cause for the rapid increase in temperatures at this time is still the subject of deep debate and largely unknown. However how very "out there" hypothesis, not even mentioned on the wikipedia page, is that this could have been when a civilization such as our experience an event more-or-less identical to our own current climate crisis caused by the rapid use of hydro-carbons.
Of course, the biggest challenge with this hypothesis is, as pointed out in the article, a civilization like this would not leave a trace on the geological record. So there's really no reasonable way to have much evidence in favor of this possible explanation.
But since here about this I've been fascinated by the problem of sending messages to the future. Suppose we come to realize that rapid use of hydrocarbons does most certainly lead to the destruction of any civilization foolish enough to tread this path. The most reasonable focus of scientific effort that would be to figure a way to warn the next advanced civilization on this planet in hopes they might not meet the same fate. But presuming that civilization is 50 million years in the future, how could this be done?
0. https://en.wikipedia.org/wiki/Paleocene%E2%80%93Eocene_Therm...