A time capsule is a container, typically buried
or otherwise sealed away, containing records, everyday objects, pop-cultural ephemera, or other items, and intended to be opened and examined at some point in the future, commonly from around 25 to up to several thousands of years later. These contents are meant to provide their eventual openers with a sense of what life was like in the past, serve as primary sources
and well-preserved artifacts for future historians, and/or to create records of contemporary culture
for the benefit of successor cultures or species, motives I suspect as not particularly foreign
to E2 users.
Given the natural human drive for immortality, in whatever form it may be found, people have been intentionally burying records and the like for ages, most commonly in the cornerstones of buildings. The modern "time capsule" fad, however, dates back to a 1938 burial at the Westinghouse Pavilion at the New York World's Fair, proposed by science fiction author and futurist G. Edward Pendray, and conducted as a publicity event. Pendray was inspired by Dr. Thornwell Jacob's similar but more expansive "Crypt of Civilization" idea, and coined the term after being convinced that "time bomb", his first name, would be less than ideal. Inspired by this example through press reports or visits to the site, thousands in America and elsewhere created their own time capsules, and capsules have been placed in parks, lawns, city hall crawlspaces, school courtyards, and the like ever since.
The primary failing of time capsules is that people often forget where they are - 3,000 decay-resistant records of the location of the original Westinghouse capsule were printed and distributed to libraries, museums, and monasteries worldwide, but the documentation of other capsules has tended to be much less comprehensive. Given that the very idea of a time capsule is, generally speaking, to create something that will outlast our fragile mortal existences, surviving witnesses to their dedication are often rare, and printed references to their location, if any remain, are as difficult to track down as any multi-decade-old records. Even if the location of the capsule is known or can be rediscovered, there still remains the possibility that someone has in the interim unknowingly destroyed it, misplaced it, built something on top of it, or otherwise rendered it inaccessible. As this has already proven to be a significant issue for the relatively short-term capsules whose exhumation dates have already come up, one must question how many of the multi-thousand-year capsules will really be recovered as their creators intended.