time capsule

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A sealed container preserving articles and records of contemporary culture for perusal by scientists and scholars of the distant future.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A sealed container, buried at some location, that contains records of contemporary life - to be rediscovered in the distant future.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun container for preserving historical records to be discovered at some future time