I had a little thought that the ice caps that we've been using to put dates on things may not be that reliable. Consider if we went through an age of warming (where perhaps something like a volcano or meteor brought the temperature back down). Then the ice would have melted and refroze - so therefore the layers wouldn't be so reliable, right?
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Dating of ice cores is difficult. It can be done through radio-isotopes, which give an approximate age of air and minerals trapped in the ice, or by counting annual layers. Something like a short warming event during which no snow accumulated and maybe some melted off would be hard to recognize, but we could still date the ice that was present by radiometric means.
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An "age of warming"? That would not be the same as a volcanic eruption of a meteor impact. If such an event took place there could be significant planet wide warming. Ice caps would be affected. However there would be a distinct horizon within the ice core that would record the event. That horizon would probably be marked but an increase in dust. It would be very distinct from the layers above and below. There are many such markers in the Greenland Ice Sheet from nearby volcanic eruptions.