I'm one of the test subjects for a new device, capable of sending an individual back to any point in history. I've been told that - due to certain problems with the process - I'll arrive naked, and so have no means of returning to the present, meaning if I want to provide feedback and/or data, I'll have to leave a message that will survive long enough to be picked up by the research teams of today. Some of the previous test subjects have already accomplished this, but they've all been sent into relatively stable time periods, where humanity was already well established, so they could get away with time capsules, hidden codes in the bible, etc. Due to my skillset as an extreme survivalist, I'm being sent back to well before humanity had climbed out of the trees - they're aiming for the Mesozoic era. This means dinosaurs (including T-Rex), and likely a whole host of other things unseen by anyone.

My mission is to a) survive, and b) leave a message that is likely to be found by my team in the present, documenting when I arrived (if I can figure this out they can possibly bring me back) along with anything else that may be of interest. This message will hopefully contain the first human account of dinosaur behaviour, but we'll see what happens.

Assuming I can stay alive, which method of storing a message would be the most likely to survive until the present, considering the earth will be hit by a meteor sometime after I arrive (not too soon after, I hope). If the message can be concealed in such a way that only my research team would be able to decipher it, that would be ideal, but is a secondary concern - for me, at least.

Note: This is not a duplicate of Million Year Time Capsule as the length of time is 65x as long, and involves meteor impacts

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Monica Cellio May 14 '17 at 3:46

21 Answers 21


Play the longest game of telephone

Instead of sending 1 person back 64 million years, send 64 thousand people back in 1 thousand year increments. Heck you could even send the same people back again and again if they are rescued fast enough.

Each person would build their own thousand year monument and try to find the previous person's thousand year monument and add the old message to the new monument.

As for the medium, it could be different every time, but I would recommend giant stones arranged in formations. https://en.wikipedia.org/wiki/Stonehenge

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    $\begingroup$ I like the idea of the sending people in reverse order (i.e. -1000 years first, then -2000 years, etc.). You'd get a domino effect paradox as 64,000 monuments - or what's left - spring into existence (or something) once you send the last person allll the way back to kick it all off $\endgroup$ – Flambino May 4 '17 at 18:03
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    $\begingroup$ If there is just 5 % probability for each traveler to fail building their monument or finding/decoding the previous one, then the success rate of the transmission is pretty much zero. I would suggest creating more duplicates of the message, or request the travellers to aim at more than 2000 years long monuments. $\endgroup$ – Tony May 5 '17 at 11:20
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    $\begingroup$ You're going to need more than one person to build stonehenge, so I'd suggest a different medium. And if 64k people is too many you could probably stretch the gaps to a fair bit more than 1000 years. I do agree with @Tony's comment though; you're going to need to allow for multiple failures in the chain or the whole thing will fall apart. But the basic idea gets a +1 from me because I can't see any other way that you're going to transmit a message successfully from that far in the past without any technological assistance. $\endgroup$ – Simba May 5 '17 at 15:43
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    $\begingroup$ It's a good idea, for sure. I think as you got closer to modernity you'd have to start dismantling those that survived, and replace them with more subtle messages, instead of always using monuments, but it's an interesting starting point to get out of the dino age. I wonder how hard it would be to make a monolith that could survive a meteor impact... $\endgroup$ – Callum Bradbury May 5 '17 at 15:52
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    $\begingroup$ @Simba Absolutely, but if said knowledgeable person also specifically learned how to make the various tools required - what kinds of natural fibers can be made into ropes, what types of wood and stone... where and how to find them, etc... Assuming they managed to survive long enough and avoid major injury, death, poisoning, etc., etc., it is just remotely possible to pull it off. $\endgroup$ – nijineko May 10 '17 at 18:00

Find the message first.

Before going back, search and find a message from your trip. Ensure that the "outside" layer has the fact that the message came from you (and only you) encoded on it somehow (using cryptography, for example). It should also include directions on where to put it, and how to make it.

The actual location you are sent to would be inside an inner layer, which you should not open prior to going back.

Then go back, following the instructions on how to send the message back to yourself.

In the present, once they have sent you back, they open the inner message and retrieve you after you in turn sent the message to them.

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    $\begingroup$ Exactly, why go through all the pain of inventing a method when time travel is a cause from effect generator? $\endgroup$ – ths May 4 '17 at 18:23
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    $\begingroup$ @ZanLynx ...*most* of those stories are inconsistent and/or plain brain-dead. Do you want to write a poor story that only uses time trave as a "gimmick" or do you want to go down the Novikov rabbit hole? :) $\endgroup$ – xDaizu May 5 '17 at 8:10
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    $\begingroup$ @CallumBradbury If we don't find it, then why do we think we will find it? But you want to know how to generate plausible plans? Take one closed timelike curve factory and a computer and a messaging system. Solve intractible problems before you pose them. Spawn technological singuarlity. Ask resulting superintelligence how to do it plausibly, then look for boxes. You have time travel. You have a cause from effect generator. Things get really weird. $\endgroup$ – Yakk May 5 '17 at 12:44
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    $\begingroup$ @AJMansfield The report exists. If the relatively easy excuse for the report to exist (you sent someone back in time to generate it) isn't true, than a lower probability excuse for it to exist (as an example, someone wipes out humanity, sees the report, and sends it back in time to fool humanity into thinking that they will do it in the future) must happen: the report (almost certainly) didn't just spontaneously form. You have an effect, arrange a harmless way for that effect to happen, or something will cause the effect. Once you have time travel, you have Bayesian leverage... be careful. $\endgroup$ – Yakk May 6 '17 at 17:43
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    $\begingroup$ @AJMansfield I don't see how is it boring. The bootstrap mechanism is that it always bootstrapped; there is no "second arrow of time" over which to bootstrap. It is also about the only time travel that is time travel and not "go to another parallel universe somewhat related to your own". $\endgroup$ – Yakk May 7 '17 at 11:56

If you've already been sent back

You're basically dead.

If you haven't

Decline the job.

Even if you survive just breathing the air you're going to have a rough time finding something you can both engrave and insure won't decay over 65 million plus years. And then you'd have to stick it somewhere where it won't get crushed, burned, eaten, moved, drowned, or sucked under a tectonic plate and melted. That task is basically impossible.

Even if you found and killed a dinosaur and engraved its bones and threw them in a tar pit, the odds that your message is found by scientists in the future are basically nil. Hundreds upon hundreds of dinosaurs (birds, plants, other animals, even one human) died in tar pits. While science has recovered and impressive collection, is it reasonable to assume that everything that fell in has been pulled back out again? Probably not.

And a tar pit is your best option. Every other fossil has undergone even more unlikely odds to get to the present.

You'd have to kill and engrave the bones of a dinosaur every fifteen minutes for twenty years and still not have a message survive.

  • $\begingroup$ There weren't tar pits in the Mesozoic era. $\endgroup$ – sphennings May 4 '17 at 15:16
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    $\begingroup$ @sphennings Tar pits were a "this is a thing that would make it easy" and even then "easy" was relative. If they aren't even around... $\endgroup$ – Draco18s May 4 '17 at 16:04
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    $\begingroup$ I've got to contend on the survivable atmosphere point, ncbi.nlm.nih.gov/pubmed/25600219. Submariners live in very high concentrations of CO2. The linked study shows no problems moving from a .1% CO2 atmosphere to a 2.5% CO2 atmosphere. Current CO2 levels are ~400ppm, Mesozoic CO2 levels were ~1100ppm at its peak. That's not as big an increase as the study tested. $\endgroup$ – SethWhite May 4 '17 at 18:51
  • $\begingroup$ @SethWhite My link about the atmosphere is to another answer on this page. Go link masterofimps that study. $\endgroup$ – Draco18s May 4 '17 at 19:04
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    $\begingroup$ @SethWhite CO2 in the air isn't a problem, like the Nitrogen, we don't really absorb it. The problem with CO2 is when there is enough to displace the normal air and so displace the oxygen. As for the atmosphere back then? O2 poisoning may be a problem, we do need it to breath, but we don't like too much, and there was a lot more in the atmosphere back then. $\endgroup$ – Baldrickk May 5 '17 at 9:16

TL:DR: you are on a suicide mission.

I'm going to hand-wavium the atmospheric concerns others have mentioned. If the air isn't breathable, you're dead long before writing/sending your message becomes a viable concern.

Others have mentioned some of this, but you need some kind of preservative agent proven to survive through the eons, and you need to make sure your preserved message is large enough and in the right spot to be found.

So you have a few overlapping strategies, but even if you land in the perfect place and get your message perfectly preserved, these are long odds.

  1. Practice survival skills. You're going back with no tools. So spend some time in the modern-era practicing how to convert natural elements to tools. How to shape stones into knives, axes, and arrow and spear heads. How to make bows and arrows and spears from trees as close to what we believe the Mesozoic era had. How to make fire. How to identify flint, since it sparks. How to trap animals. You're going to need these skills, since you have no safe way to identify safe-to-eat plants once you arrive. Hopefully, you can survive on the meat you can catch.
  2. Location, location, location. Hopefully, your time machine can place you with some precision. You will have no landmarks when you arrive. Even the mountains will be vastly different 65 million years ago vs. today. The continents won't occupy the same latitude and longitude, nor have the same coast lines, so you won't be able to place yourself on that world in a known location on this world once you're there. But you need to find a place that's known for fossils. Utah, California's tar pits, England's Jurassic Coast. Find an area where fossil hunting is popular, because that improves your odds of your message being found.
  3. Make your message large. The larger your object, the greater the odds someone will see it when digging for fossils.
  4. Make your message durable. Find some flint or similar rock and chip away at your message in a block of hard wood or stone. Or if you think you'll have the time, try to make it in clay and sun-bake that clay to harden it.
  5. Double bag it. Take your clay, wood, or rock message and coat it thoroughly in tree sap. Multiple coatings will be required, but build up a thickness and sun-bake it as much as you can to try to dry it out. An amber coating will help prevent damage to your engraving and make sure the source material doesn't degrade. You can also embed some of your hair to provide DNA samples. This will prove you left the message and not anyone else.
  6. Triple bag it. Wrap your tree-sap-coated message in leaves and tie it off in a bundle. Then drop your package in a tar pit or a push it deep into mud pit. Leave lots of foot prints, as those get fossilized, too.
  7. Rinse and repeat. Try to bury more than one copy in more than one location. Don't rely on a single message to survive and be discovered.
  8. Don't get eaten or trampled or gored. While you're busy doing all the above, make sure no predator decides to eat you for elevensies and no herbivore tramples you in fear/defensiveness. That's kind of important.

In addition to that, there are two additional points worth mentioning:

One, timing.

We know when the meteor fell and formed the K-PG Boundary to within a margin of error greater than your lifespan. From Wikipedia:

In a 2013 paper, Paul Renne of the Berkeley Geochronology Center reported that the date of the asteroid event is 66.043 ± 0.011 million years ago, based on argon–argon dating. He further posits that the mass extinction occurred within 32,000 years of this date.

That's a range of 22,000 years, according to our best estimates. Your odds of witnessing the impact are minimal. In fact, there's a 50/50 chance you'll arrive after the impact.

two, population density

There's also the question of whether you'd see any significant, large, dinosaurs at all. We simply cannot say with certainty what the population density was for any given period of the age of dinosaurs. One estimate I could find was:

He and his colleagues focused on what would be the western United States during the late Jurassic period, 160 million to145 million years ago. His best guess is that there was an upper limit of a few hundred animals across all shapes and sizes per square kilometer, and up to a few tens of large sub-adults and adults.

Looking beyond the numbers of plant-eaters, there were probably even fewer meat-eaters. "Whatever the true densities of the large herbivores were, large carnivore densities would have been 1 to 10 percent or so of those values,"

I don't think I'd volunteer for this assignment. But I wish you luck, soldier.


Your bosses will tell you where to leave it.

Face it; they've already found your message, or at least the place you're supposed to leave it. How else would they know where to look for it? They probably haven't told you about it, because paradox or something. They just know where it's supposed to be. If it is there, cool. They'll tell you where to put it, and what to use to make it.

If it isn't there, they're not telling you that, because that means you're dead--you weren't able to leave the message.

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    $\begingroup$ Well, hello there, Novikov :) $\endgroup$ – xDaizu May 5 '17 at 7:52

This answer relies on a paradox, so may be invalid, depending on how you wish to resolve time-travel paradoxes in your universe.

Without paradox, the proposal seems to be: Simply agree on the basics of where the message will be deposited (a specific tar-pit, for example, or other known fossil depository). Make it a tar-pit which is currently being investigated, so you know they are finding things there. Go back in time.

With paradox, it becomes: Go dig there. Get the message. Then go back in time. This will tell you that you will succeed in your task, before you embark on it. This is a paradox.

Depending on how significant you want the paradox to be, you could also read the message, and be sure to note on your message which knowledges would be useful in the land, that you did not possess at the time of reading the message. Then you could go off and get that training, then go back in time.

In fact, you don't even know you were planning the trip, or that time machines even existed, when you read the plaque.

  • Director Stevens: [in an open-air office under a simple marquee, bare sunbaked wilderness to the horizon] Jones! About time you got here. We just pulled this out of the pit. Is this your idea of a joke? [hands Prof Jones an engraved, amber-encased plaque, bearing his name, a phone number, and detailed notes].
  • Jones: Definitely looks like someone's idea of a joke, but not mine. Let's call the number. [dials]
  • Phone: Good evening, this is BRICT of London, Dr Smith speaking.
  • Jones: Hi, this is Professor Jones, I just found a plaque with my name and your number on it.
  • Phone: This is probably best handled face to face. Please hold on a moment, I'll be over to speak with you immediately.
  • Jones: I very much doubt that, I'm out in the field at the Tanzania tar pit dig.
  • Phone: click
  • Jones: What a strange fello...
  • Smith: [Pulling up in car] Good afternoon, Professors Stevens, Jones, I'm Dr Smith. We were just speaking on the phone. You mentioned a plaque?
  • Director Stevens: How did you get here so fast?
  • Smith: Ah, terribly sorry, I'm from the British Rail Institute of Chronological Transportation. Arriving precisely on time has rather become our forté.

Replace a bone in your body with a prosthetic material

Here's one potential idea. Replace a bone in your body with a prosthetic material, with a portion or perhaps all of it composed of a predictably decaying radioactive isotope. It very much depends on how close a time you need to record to that will depend on the material, as the half-life of the isotope in question will determine the material. You could have a number of different isotopes also to determine the age from long half lives to shorter.


This wont solve the problem with needing to send more detailed messages, but it might help establish a reasonably accurate date from which you can be retrieved from?

Edit: I had originally also stated that the Mesozoic era atmosphere wouldn't be survivable by humans, but after some further research I found this wasn't the case. (Thanks @SethWhite !)

  • $\begingroup$ But remember that you want to survive and let your team track your time coordinates to pick you up. The bone has a disadvantage that you have to sever your limb to leave the message (if not die outright). There is also the problem of storage - unless you know a geologically safe place, the bone would be crushed, submerged or buried deep underground. $\endgroup$ – Radovan Garabík May 4 '17 at 14:19
  • $\begingroup$ @RadovanGarabík Well the bone itself may allow for reasonably accurate timing just by its existence (it would be dated when found using the various isotopes - though the precision wouldn't be great admittingly, but may be helped with the fact that the exact original quantities and compositions are known to begin with), which would of course be after death (there's a time travel paradox here). As for a geologically safe place, you're absolutely right, it would just be luck that it gets discovered, never mind survive the earth reforming itself over the millennia. $\endgroup$ – masterofimps May 4 '17 at 14:52
  • $\begingroup$ @RadovanGarabík As a further thought, some materials can be detected from space, even when underground (but not very deep underground), and this may help locating the bone $\endgroup$ – masterofimps May 4 '17 at 14:55
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    $\begingroup$ I've got to contend on the survivable atmosphere point, ncbi.nlm.nih.gov/pubmed/25600219. Submariners live in very high concentrations of CO2. The linked study shows no problems moving from a .1% CO2 atmosphere to a 2.5% CO2 atmosphere. Current CO2 levels are ~400ppm, Mesozoic CO2 levels were ~1100ppm at its peak. That's not as big an increase as the study tested. $\endgroup$ – SethWhite May 4 '17 at 19:40
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    $\begingroup$ @SethWhite Thats a really interest paper, thanks I hadn't ever heard of research done on humans in high CO2 levels (though in hindsight this would surely be a factor for submariners, astronauts etc.). As for the CO2 levels, the most cited paper shows it to be between 2225 ppmV and 1480 ppmV in the Mesozoic era, but actually examining the paper you cited and others, it seems that the Mesozoic atmosphere would have been a bit uncomfortable but definitely survivable. Many thanks for the correction ! Answer Edited ! $\endgroup$ – masterofimps May 4 '17 at 20:09

First of all, before you go back in time, you should go to a museum and search for a skeleton of a big carnivorous dinosaur (e.g. T-Rex). Find out where they have found the dinosaur.

When you arived in the Mesozoic era find that place and write all the information they need to rescue you on a giant leaf (you might have to find e.g. charcoal for this). Next step is, find resin and stick it around the leaf (it will fossilize to amber). Last and most important step is, get eaten by the dinosaur you've seen in the museum.

They will find your message inside the dinosaur and rescue you before you get eaten. I know this might sound contradicted because you have to die in order not to die, but that's how time travel works.

On second thought you don't have to die, just make sure the dinosaur eats your message.

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    $\begingroup$ Welcome to Worldbuilding SE! Given not least the effects of plate tectonics (continents moving around), how do you propose to even find the location where the dinosaur skeleton was found? Let alone guarantee that the individual dinosaur you encounter is the same one that they found? Similar issues have been discussed by previous answers to this question; you would do well to edit your answer to address that at least to some degree. $\endgroup$ – a CVn May 5 '17 at 8:04
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    $\begingroup$ According to Novikov, if the message will be there, the message is already there, so you might aswell look for the message on the dinosaur before traveling. If it's not there, it means you will have failed in your process, either finding the dinosaur or attaching the message. Keep searching for dinosaurs on museums until you find a message. When you do, you'll know which one to look for. Also,you will know what to write on the message, so that saves you some thinking! If you dont find any, don't bother traveling, you'll fail. $\endgroup$ – xDaizu May 5 '17 at 8:04
  • $\begingroup$ I'm not sure how I'd identify the dinosaur once I was back in time $\endgroup$ – Callum Bradbury May 5 '17 at 10:59
  • $\begingroup$ @xDaizu: when you fin the message, just take a picture of it and hand it to your colleagues before you go! $\endgroup$ – Emilio M Bumachar May 5 '17 at 13:17
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    $\begingroup$ @xDaizu "If you don't find any, don't bother travelling; you'll fail." Which is the most probable outcome. You don't travel, so you find nothing, so you don't travel. $\endgroup$ – wizzwizz4 May 7 '17 at 10:52

TL;DR: Locate the Canadian Shield and mess with the uranium deposits.

Your chances of survival are low, but let's give it a try. Before you go, interact very, very well with geologists. Hopefully, in your age, we know with more precision and accuracy than today the geological history of Earth. 100 million years ago, the continents were pretty close to each other:

100 million years ago
Source: Wikimedia Commons

Hopefully, in your time, we will know those coastlines with more precision. Of course you will have memorised this map, so in a couple of years of exploration you will have a reasonable idea of where you are in the contemporary world map.

I will assume your extreme survival skills are good enough to use the resources available at the time to build a raft and cross between the continents.

100 million years is a long time but parts of the Canadian shield are billions of years old. Although the shield has moved around, whatever message you try to leave must be located on such a spot or it will have no chance of surviving plate tectonics, subduction, volcanism, etc. By now you will be able to identify where in the world the shield was at the time. Alternately, parts of Africa will also work; did you notice how similar Africas shape is to today? Perhaps not all is as hopeless as it seems.

Now comes the difficult part: how to hide your message? On the one hand, you want your message to survive. On the other hand, you want it to be found. Those are conflicting requirements. On top of that, you have no technology. The Shield has plenty of uranium. Do you think you could develop the tools to (1) locate the largest uranium deposits, (2) dig them up, (3) rearrange them in a funny shape, and (4) bury them again? On the Shield or another ancient part of the planet, that might actually survive. Other methods have been mentioned, but the key is to choose the right location. In most of the world, a capsule will not survive. In some places, it can.

Good luck.

  • $\begingroup$ Awesome, I'd never heard of the canadian shield before, and this seems to solve the main issue of ensuring survival across aeons. My time period is the modern day, with no real differences other than a group of people having created a time machine, so as to developing tools to locate uranium, it depends how feasible that is using raw materials today. I wonder if it would be easier to find back then (there must be more digging required today, I imagine)... $\endgroup$ – Callum Bradbury May 5 '17 at 10:52

Cave paintings.

While you can never be sure when or where a stone from space may hit, and a lot of other things are very uncertain, you have the great advantage that you know the future before it becomes your future.

Identify and agree on a likely cave as well as a code that can easily be produced with stone-age ressources, while also looking reasonably inconspicious to uninformed people, including nosy anthropologists.

So you will probably be limited to arabesques and hunting scenes. While it may sound boring, a lot of data can be put into a hunting scene if you know what to look for. The exact pattern of deer on the wall may be a star chart, the angle at which the spear is flying, the distance of objects from each other, size, the numbers themselves, all these bits are data.
For an uninformed observer it looks like a hunting scene. For the recipient of the message it is all the data you need to transport your stories.

Obviously if you are reasonably sure your cave will remain mostly undisturbed, you can also create a large mosaic from rubble and pebbles, using a binary code if necessary, and cover it in a thick layer of dirt to prevent it from being disturbed by wandering animals.
The recipient will know where to look and simply remove the dirt layer to read what you had to say to them.

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    $\begingroup$ Of course, first you have to find a cave whose existence is known to encompass both the Mesozoic and the present. You know, like more than 65 million years. Could you please inform us of the location of such a cave? Like, even one? $\endgroup$ – WhatRoughBeast May 4 '17 at 10:38
  • $\begingroup$ @WhatRoughBeast Being no expert on the field, but remembering reading about caves with paintings that are supposed to be very old, i assume that there should be a cave somewhere that qualifies. Where that is i cannot say. But it does seem plausible to me. After all, you have an entire planet at your disposal. $\endgroup$ – Burki May 4 '17 at 10:43
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    $\begingroup$ If you are thinking (for instance) of the Lascaux paintings, they are about 40,000 years old. That is not remotely the same as 65 to 250 million. $\endgroup$ – WhatRoughBeast May 4 '17 at 10:47
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    $\begingroup$ To remain undisturbed from the forces erosion for 65 million years seems immensely unlikely given earthquakes, floods, cave-ins etc. Especially given the dramatic shift the continents will take over the next 65 million years, $\endgroup$ – Firelight May 4 '17 at 11:10
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    $\begingroup$ smh.com.au/news/national/… suggests that there are caves old enough. You can afford cave ins if you can somehow re-find the cave say with radar, they might even help with the erosion problem. $\endgroup$ – user25818 May 4 '17 at 21:10

I have an idea that depends on how much evolved is tecnology on your world (I mean, if they can send someone to mesozoic age, I guess it is pretty advanced).

I saw that @masterofimps suggested to replace a bone in your body with a prosthetic material. I'll go a little further. If you get an arm or an leg replaced, let's say it has some kind of pocket to store a small device, a space probe. Or maybe the the entire arm or leg could be a space probe.

Let's think of an arm, to be simple. On the arm, there could be some input data device like a small keyboard, so you could write on it's HD. When the time comes, you take it off (the arm or just the device) and launch it to space and it will stay on a programmed orbit. I saw most of the comments, and it's a fact that Earth will change too much to leave a message there. So leave it on space. The only thing that can happen is it been hit by a meteor on some human satelite hit it on launch.

I belive it's a better shot than leaving it on Earth. Human satelites should be well documented through history, routes, time of activation, deactivation and so on. They could trace a route for your device that avoids it all and leave it programmed. That could also be done partialy with asteroids. When humanity can predict where exactly meteors will enter atmosphere they probably will document it too, so those can also be avoided.

I enjoied your premisse. Good luck!

  • $\begingroup$ Welcome to WorldBuilding! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$ – Secespitus May 4 '17 at 17:16
  • $\begingroup$ Thanks for the suggestion, the problem is anything not organic, within the field when you teleport, will get mashed up when you re-emerge, possibly within your body. I don't think taking artificial limbs would be a good idea in that scenario. $\endgroup$ – Callum Bradbury May 4 '17 at 18:56
  • $\begingroup$ I see, that makes It harder. $\endgroup$ – Guilherme May 4 '17 at 19:07
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    $\begingroup$ @CallumBradbury You might want to define what exactly counts as organic and part of the body. I mean, there's bones, there's teeth and hair, there's content of the bowels... unless you invoke arbitrary magic, or just hand-wave it and hope readers suspend their disbelief, there should be engineering way to bring something along. Simple ceramic/bone knife or medicines would be a huge asset. Or bring a dog along. Omedicines. $\endgroup$ – hyde May 5 '17 at 4:49

Nothing unless you know where you are or are willing to play long odds.

Basically unless you have satellites to map the planet you are going to be guessing with extremely long odds. Even with satellites your still going to have problems. And even then your only option (besides the satellites themselves) is stone carving. Your real issue is you have no idea where anything ise or if the thing you are looking at is going to be a fossil or not. Out of millions of dead t-rexs only a handful ever fossilized and only a handful of those were ever found.

metals will not survive, (corrosion, dissolving, ect) and would be prone to collection and use in tools in early history if they did. paint has even less chance, stone carvings placed in a depositional environment is it.

If you know where you are your best bet is to find the solnhofen reef/lagoon system in germany, carve a thousand copies on stone tablets (don't use local stone) build a raft and then drop them all over the place in the lagoons. Lots of copies or just lots of notes is your best bet, just make lots of tablets and drop them in any depositional environment you find and you increase the chances that some will be found, but it is still long odds you don't know what is going to be eroded away or not be exposed.

  • $\begingroup$ I wonder if you could artificially induce fossilization, I agree it'd be a long shot, I suspect every option would be, but the best long shot could probably be used with some tweaks to the setup $\endgroup$ – Callum Bradbury May 4 '17 at 14:38
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    $\begingroup$ the problem is not getting something to preserve its getting it found, so much is destroyed by erosion or never gets exposed to be found. I real kicker is what happens if they are found before dinosaurs are named and the names you use never get applied to anything. Or if they get found before your language is invented and they become another indus script. $\endgroup$ – John May 4 '17 at 14:54

This is only a seed of an idea, but perhaps you can alter the DNA of living creatures to hold the contents of your message.

Life has been continuously in existence (even through massive extinctions) for 4.1 billion years on this planet. It survives through cataclysms, impacts, volcanoes, and changes in the surface of the earth. It can carry your message for you.

My first thought of how this is done is via a custom virus implanted in a "living fossil" like a coelacanth, which then propagates to others of the species via contact and reproduction.

I am a little short of ideas on how you get the virus into a fish that lives on the ocean floor. Also, you would probably need to infect a lot of fish to ensure propagation to the future.

  • $\begingroup$ You would also have the problem that over 66 million years and probably tens of millions of generations, chances are pretty low that your altered DNA would survive even somewhat intact. At best. $\endgroup$ – a CVn May 4 '17 at 20:41
  • $\begingroup$ "Oh I wish I wish I hadn't squished that fish." Be careful with that mutagenic virus: If you accidentally spark the rise of the mammals you are your own fault. $\endgroup$ – user25818 May 4 '17 at 21:18
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    $\begingroup$ Good idea, one question: How do I alter the DNA of creatures whilst naked with no technology? $\endgroup$ – Callum Bradbury May 4 '17 at 23:18
  • $\begingroup$ If you have an estimate of the error rate you could encode it with Reed-Solomon error correction of appropriate strength. $\endgroup$ – Carlos May 5 '17 at 7:14
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    $\begingroup$ You yourself are infected with the virus, and a drop of your blood transmits it. $\endgroup$ – jared.dahl May 5 '17 at 12:49

The time of the dinosaurs (around ~100 million years ago) is so far away, even the landmasses are totally different today. A cave with paintings would probably not survive that long.

But as there are some petrified bones and amber from that time found, I would propose writing A LOT of messages in near-dry tree resin and some bones. Then hope for the best. As you yourself would probably find your messages in the future with your team, you know if you've written enough messages before you're sent back in time.


Amber comes to mind as a very convenient and effective way of sending information through time, just cut up some Mesozoic coniferous trees or suchlike and then you can coat information containing things in amber, code could be scratched into some sort of rock; I assume these scratches would be fossilled at least as well as insects. The problems with this of course would be the fact that it would be, if not discernable to others, fairly obvious you amber fossilised code stone contained information, so you would need to find some place to bury/hide said fossilled code where it could be found by you only (inside a really deep hole/cave?) This is assuming you know the location you are sent back to corresponds to the location in the present you travelled from, but if you didn't, (which would be more exciting for a story anyway, in my opinion), a possible way of signalling the approximate location of the main information deposit site would be to deliberately fossilise lots of dinosaurs/trees ect in an area around or near the main site, or in an area nearby that specifies the location or the main site somehow by the arrangement of fossils.


T-rex - 68 to 66 million years ago. Finish of creation (for example) Tatra Mountains that are a part of Alps were formed 10-15 millions years ago. So depending on a place you have like 50 millions years of tectonic movements, oceans moving in and out, glaciation and other things like volcanos.

So even if you had a material that could survive that long being crushed, mauled, heated, cooled you still will have one large problem:


It's not like you gonna leave a note "At the top of Mount everest". Good luck, Mount Everest wasn't even there.

So, the scientist would need to figure out how to time-travel self propelled satellite that would survive those 66 millions years, so they could map what on earth is earth. And then they would decide "mmmm no, better not send human back there, they're useless"

  • $\begingroup$ Hmm. Maybe there are places that are known to rise only in the last 66 million years? I'm not a geologist, but it does not sound totally impossible. $\endgroup$ – Jens May 7 '17 at 20:29
  • $\begingroup$ Greater Khingan Range was done in that time but then you would have 66 millions years of things growing on those places. And mentioned weather. $\endgroup$ – SZCZERZO KŁY May 8 '17 at 8:02

Do your research

Identify several sites near your proposed destination (temporally and geographically) from which fossils have already been recovered. It doesn't matter so much what kind of fossil it is, as long as it would have been there at the time of your trip. Ideally you're looking for sites with extremely well-preserved, intact skeletons, since you know that those areas will remain undisturbed until the skeleton is found.

Preserve your message

Others have mentioned amber as an excellent material for preserving your message; another good choice would be inside an eggshell. Amber and eggs are always examined during digs, so your message should be found and identified.

Use distinctive materials

You'll want to carve your message into a material that wouldn't normally be found in the area where you'll be burying it. Igneous rock in a sandstone area, for example. This will ensure that your message stands out from the surrounding rock, and that it's easy to remove the rock matrix from your message tablet.

So, take your message, carved into a piece of granite and stored inside a dinosaur egg filled with sand, and bury it directly over the remains of a dinosaur you know will be excavated in the future. Make sure you've actually carved the message into the stone, not just scratched it onto the surface.

Then sit back and profit!

...Or just plan ahead

If you want to be absolutely certain your message will be received, and received ONLY by your own people, you have an even simpler method available. Identify a formation of sedimentary rock without too much folding, and make sure you can identify the same region when you go back.

When you're ready to send your message, carve it into igneous rock (as described above), pack it into an eggshell with sand or clay to protect it, and bury it in the region you'd previously identified. You KNOW this formation will remain intact, after all.

After you've gone back, your research team can return to the formation you'd already arranged to use and dig through it for your message.

  • $\begingroup$ I like this idea a lot, there'd be a high chance of interception by others before the research team could get their (our?) hands on it though, so I'll avoid marking it as the answer until I see if anyone solves that problem too. Thanks for putting in the time to answer :) $\endgroup$ – Callum Bradbury May 4 '17 at 19:00
  • $\begingroup$ @CallumBradbury If interception is an issue, there's another way - edited the answer with another option. $\endgroup$ – Werrf May 4 '17 at 20:24

Use a nuclear reactor. https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor

It mentions that we can determine the timing of the heating cooling cycles based upon the concentrations of trapped xenon isotopes. These cycles are controlled by the influx of water.

Go hear, create a damn. Adjust the inflow of water. Use that as a way of high level Morse code. Unfortunately you have to go back 1.7 billion years.

Alternatively, make trees like this of several distinct genetic varieties that are self-sustainable. Creating wood actually as hard as granite

Put seeds of each of these inside of the time traveler. Eat them, stick them under the skin, or use any drug trafficking tricks. The trees will have to grow over a large area to ensure entering into the fossil record. Start at the west coast, grow a grove and start moving east planting different groves.

If you go back with 256 different seed types, and then encrypt you message based off cross breeding 1 type with one of the 254 other types each grove contains 65,024 bits of information or approximately 8 kilobytes.

Either option probably requires intense study/training before hand and an index/code book tattooed on their skin.


Paradox? Naa. If you haven't created the message yet, it won't exist yet. Your best bet is to determine a location based on a star chart. Don't try to use geographic locations. Like others have said, the geology will be unrecognizable. Agree on a location with your peers, it will limit their search area to a few thousands of square miles.

I like the idea other have had of swallowing seeds that you will need to either create a message or sustain your life. But I imagine you will need to live a nomadic life to complete your mission. That said, others recommendations for message preservation sound like your best bet. But to improve the odds of mission success, they should probably send 10-20 people back with the same machine settings in hopes that at least one message gets through.

Modern English is probably cryptic enough that if anyone found it, it wouldn't be decipherable, so coding wouldn't be an issue.

I think the largest hurdle would be having the message intercepted by well meaning explorers before your team arrived. It is likely that the message would be found and kept in a private collection that they will never see.

  • $\begingroup$ A star chart won't be helpful. 100 Ma ago -- that's more than half a galactic rotation. The night sky would be unrecognizable to a homo sapiens. And with precession around the galactic pole in ~30000 years, no one could tell you where the equivalent of a Northern Star could be. But you could make some observations to find one :-) $\endgroup$ – Jens May 7 '17 at 20:24

Ask your scientists if they have heard of the Wait Calculation and insist that you are being sent not until they have improved that other device (that will be used to rescue you) in a way to track your space-time location better than what they have now so rescue at any time is possible.


Since you are going to need to store the message in something that has a good chance of being reasonably intact tens of millions of years later. Given the immense amount of geological upheaval in the intervening time things like caves are probably out but we do know of somethings that have survived (relatively) intact - fossils.

Unfortunately finding a specific organism that we know is subsequently fossilised and discovered is going to be essentially impossible (especially given you aren't going to have any fancy tech with you) but what you could do is play the percentages by creating your own fossils - lots of them.

Start with the list of areas that would be survivable in the destination period, large chunks of the time period when dinosaurs were active aren't very friendly to humans but the late Cretaceous (~66 million years ago) should have dinosaurs and decent swathes of human-habitable climates.

Then you need to narrow down that list to areas that have the right sort of conditions for fossilisation at the time you are heading for. This part isn't easy as with current technology we can only pin down fossil ages to about a 5% margin of error, which sounds pretty good - until you realise that 5% of 66 million years is 3.3 million years so you'll probably want to do some hand waving around the time-travel technology vastly improving the accuracy of dating fossils. Now from that list you can pick your time and place and travel back. You'll have to be very accurate both geographically and temporally because navigating to a specific area once you're there is going to be nigh on impossible - the landscape is going to be completely different, even the stars are going to be pretty different!

Once you've arrived you then just need to take advantage of the good fossilization conditions and create lots and lots of fossils that contain your message, carving the information into bones is a good bet, you can do it with minimal, improvised tools and it should hold up fairly well. Although it will be rather limited in how much you can convey and hiding what it is will be very difficult because paleontologists tend to look rather closely at fossils and there's no guarantee that the "right" people will be the ones to find one of your DIY ones.

Then back in the present (future?) your organisation collects as many fossils as possible from the target area and inspects them all for any messages you left.

I know you said in the OP to assume that you can survive but I think it's worth mentioning that survival is going to be the biggest challenge. Arriving naked with nothing to help you is going to present a serious challenge! Even the best wilderness-survival skills from the human era are only going to go so far - you'll have no idea what animals or plants you can eat safely and even getting drinkable water is going to take some effort. Add in the predators, insects, and the distinct possibility of pathogens to which you have zero immunity to and the odds of surviving more than a few days let alone being able to do any useful scientific observation and message writing are going to be pretty negligible!


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