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Setting: Modern day Earth, no special technology advancements.

Situation: On day, in a relatively populated American city (the specific city is unimportant...the purpose of this point is that it's high-visibility), an apparent nuclear explosion occurs and absolutely levels several blocks.

Video footage recovered from streamed cell phone footage (all storage devices in the area were destroyed) at the time of the detonation shows that it originated out of thin air, about five feet off the ground, in the middle of the street.

The destruction is almost absolute within the radius of the explosion, with almost everything pulverized to dust and/or incinerated.

However, in the dead center of the crater, rests a mostly intact human arm. The skin is charred, but the tissue within is almost untouched. The arm ends just shy of the shoulder, cut cleanly at the molecular level; the cut is not charred/cauterized. The hand was found gripping a piece of paper, charred beyond legibility.

Additional Info: Unknown to people in the present, the arm belonged to someone from about 500 years in the future.

Question: Given the full focus of the global scientific community, and all the resources America and its allies could bring to bear, what could we learn about an arm in that condition?

Assume there are no implants within the arm, its former owner had no artificial genetic modifications, and that the fingerprints and fingernails were burned off. Also assume that it took twelve hours for the arm to be retrieved and placed in cold storage.

The arm was charred by external heat of about 2,000 degrees Celsius, rather than the 100,000,000-degree temperature of the apparent nuke. There was no radioactive fallout from the explosion, and the arm has suffered no radiation damage (beyond that experienced in day-to-day life).

Specifically, would we be able to determine that it's not from our time? Would the intact blood, bone, and muscle tissue allow us to guess at the diet, age, gender, or even occupation of the person it was once attached to?

Would an adult's arm, after being detached for twelve hours, still contain intact DNA to sequence? Would the blood still be viable for analyzing the white blood cells (ie, to determine immunities)?

I'd like to stick to concepts grounded in present scientific/technological understanding, but I'd be open to including speculative technology which may reasonably be invented within a year, in direct response to such an event.

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    $\begingroup$ Jurassic Park takes it too far, but the point made there is valid: in situations normally encountered, DNA holds up very well. So assuming that the DNA survived the initial incineration (which seems very likely given the outcome described), it's highly likely that it is intact enough to sequence with good results. Blood analysis may or may not be plausible, but DNA analysis definitely should be. $\endgroup$ – a CVn May 6 '16 at 13:18
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Even without intentional artificial DNA modifications, chances are overwhelming that the arm would contain unknown antigens and/or antibodies (think 500 years of Coronaviridae reshuffling - and that's from flu alone).

The sex, age, ethnicity and probable physical outlook of the owner could easily be determined from DNA and bone assays.

Diet would be tricky; the best it could be done would to assess whether the owner suffered any of several dietary deficiencies.

Occupation would be next to impossible to determine, unless it resulted in specific traces (weight lifting can be detected, and scars from several sports can be identified if present. Rowing could be determined from a pattern of calluses, even if the heat burned them)

The simple fact that the arm was there would hint that it either appeared after the detonation or that something was able to protect it against a nuclear explosion. In both cases we're talking super-science. However, scientists would surely perform a full isotope spectrum analysis (both to determine whether it appeared during or after the explosion, and to assess the characteristics of whatever preserved it from the nuclear fireball), and would get absurd results.

Some of those results might be ruled out as contamination from the nuclear explosion, but some won't be consistent with the effect on everything else, not even postulating a "magic shield" to protect the arm.

I suspect that very soon, since isotope ratios are closely linked with elapsed time, and so they would already be thinking "time", some researchers would put forward the hypothesis of time travel. Another hypothesis would probably be a human somehow born and raised in a solar system far, far away, with a different isotopic composition than Sol's, and where divergent evolution would explain the DNA modifications. Even so, many very small divergences would be there, of the kind that is associated with evolution; the DNA would be too close to human actual to have come from too far away in space. Unless the super-scientists responsible are also naughty pranksters.

At that point the nuclear explosion would probably be hypothesized to be the result of a botched time traveling (or long-distance teleport) attempt.

Among the things a very secret, very dark government project might try to do would be to locate any relatives (or ancestors) of that DNA on contemporary Earth through large-scale DNA mapping (expect dirt cheap kits to test your DNA for anything to suddenly appear from the newborn Cheap Intracellular Analysis Ltd. of Langley, VA). Worst case, they gain nothing. Best case, they can make contact with either super-scientists, alien abductors, or time-travelers.

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Pavel and Youstay have already told you that we can find out a great deal about the person that arm belongs to. I'd like to point out a few things that they have so far missed, however.

Consider that this person is going to live 500 years from now. In this time new diseases will come into existence. Humanity will develop new vaccines, and cures for those diseases, as well as simply develop immunity to some of them.

Furthermore, and this is a biggie, we are experiencing the dawn of genetic alteration and manipulation. So called "designed babies" who's DNA has been edited to give them certain color eyes, hair, to filter for certain genetic markers indicative of disease, etc. - it's all within our grasp (or soon will be).

First of all, I think we may actually be able to get a blood sample out of the tissue. Even if it's only dried blood, scraped off of the inside of the veins. Within that blood we may find antigens to diseases that we don't even have today. Or antigens that deal with diseases we don't know how to cure today (such as some forms of cancer). Maybe even traces of nano-bots (maybe organic ones within the blood stream) which were keeping this person's body in good health.

We may also notice that their DNA is eerily flawless. Maybe less decayed than it should be, indicative of a longer life span (maybe an artificially prolonged one by having nano-bots clone cells rather than having them decay as they multiply over our lifetime).

There will be all sorts of little hints within this person's DNA and blood which will scream out to an expert that there's something "off" about that tissue.

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Here are the things you can determine about the arm, considering that the tissues inside are intact and not destroyed. Also considering the arm has not been subject to intense nuclear fallout as you would expect after a nuclear explosion.

1- The genetic information of the person. Yes, cells deep inside the arm (bone marrow) will retain genetic information which would be easily readable in all detail.

2- The gender of the person. This would be possible to determine not only from the dna, but also from the bone density.

3- Since the genetic information would not be destroyed beyond recognition, it would indeed be possible to theorize that the arm does not belong to anyone of our era. This would be possible by comparing the arm's dna with the dna of all modern day males. Dna undergoes mutation as a more or less constant rate. The dna of this person's arm would indicate more genetic mutations than those of any modern day person. The researchers can then work their way to determine roughly how long in the future would this sequence of dna come into being.

4- The race/skin color of the person. It happens that inspite of genetic mixing between all the peoples of the world, it is still possible to determine (from dna) if a person is white (caucsian), black (african), brown (south asian), red (native american), orange (south american) or yellow (east asian). So the researchers would be able to tell what race did the deceased belong to.

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  • $\begingroup$ There is insufficient change of DNA over time for a mere 500 years to make a difference beyond what is normal for different populations over distance in the same time frame. You could not tell a 14th century person from a21st century person by sequencing DNA. $\endgroup$ – pojo-guy Jul 22 '18 at 18:30
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I will put my 5 cents of basic scientific knowledge:

Possible to find

  • We will be able to extract DNA. Especially if there is some blood left in the arm. I think we could also use bones for DNA
  • We would be able to say the arm belonged to male or female. I think that we could guess height and age of arm owner with very small error margin
  • Cutting method used on the arm

Plausible to find

  • From DNA sequencing we could get biological relatives. But current DNA repositories are not that big, so actually getting come relatives is on edge of plausibility
  • Vaccines and/or any medications: This could give us an alarm ring that we are dealing with something unusual.

Impossible to find

  • The fact, that the arm comes from the future. For that there has to be some gadget on the arm (watch for example)
  • Since I am still writing this when you are getting some response: I doubt that not being able to find any relatives would lead to conclusion, that this arm is from another era in the future. As said, our DNA repositories are too small to tell this
  • But also, bear in mind, that even today people are experimenting with drugs, and any chemicals in blood would be at too low potences, that I doubt it would trigger something
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