system
Given the following post, respond as if you're commenting on Reddit:
human
What would remain of a human body after nine thousand years?

If, say, someone died in the middle of a tundra nine thousand years ago, what would their remains look like today? I assume they'd be completely buried, much like ancient cities are today.

What if they died in a cave at the snowy peak of a mountain? 

What if the entrance to the cave collapsed and their body got sealed off from the outside world? How preserved would they be? Would they go through mummification?

Would a person's skeleton survive that long?

I've, so far, asked three subreddits (two of which were incredibly helpful) and I figured this'd be the best place to ask. Thanks in advance!

PS: I used the Archaeology flair because I felt that'd be the most fitting, mummies n' all. The next ones I'd pick'd be Anthropology (because of Forensic Anthro.), Biology and Human Body.
gpt
Hi, archaeologist here.

We'd find nothing of the person that died in the tundra. Their body would be eaten by all kinds of animals, insects and microbes.

The cave on the snowy peak might or might not save someone's body. Is it permanent snow or does it melt once a year? What altitude is it: does it harbor many animals that eat meat or not? Is the cave warmer that the surroundings outside? If it's seasonal snow, we'd probably still not find anything. If it's permafrost, and it freezes in the cave too, we might find a mummified, freeze-dried body, provided it didn't get disturbed by animals.

With the cave entrance collapsed, the body would probably be isolated from the cold and still decay, at least as long as there's oxygen. The skeleton would be left though because that needs more to decay than just soft tissues.

Human skeletons can survive 9000 years if the conditions are *just* right. More often than not though, permafrost isn't all that permanent over 9000 years, deserts don't stay deserts for 9000 years and bogs don't usually stay bogs for that long. So even if the circumstances are good for preservation in the beginning, climate change and landscape change (earthquakes, floods etc) will change the circumstances and suddenly animals, insects and oxygen will have access to the body and it will still decompose. 

In very rare circumstances though, when the environmental factors don't change after decomposition, we can still find a "silhouette". The decomposition chemicals cause discoloration of the soil and we can still make out the way the deceased person laid and do some microbial sampling. The body itself is still gone though.