A Knowledge Ark (also known as a doomsday ark or doomsday vault) is a collection of knowledge preserved in such a way that future generations would have access to said knowledge if current means of access were lost.
Scenarios where availability to information (such as the Internet) would be lost could be described as Existential Risks or Extinction Level Events. A knowledge ark could take the form of a traditional Library or a modern computer database. It could also include images only (such as photographs of important information, or diagrams of critical processes).
A knowledge ark would have to be resistant to the effects of natural or man-made disasters to be viable. Such an ark should include, but would not be limited to, information or material relevant to the survival and prosperity of human civilization.
A Lunar ark has been proposed which would store and transmit valuable information to receiver stations on Earth. The success of this would also depend on the availability of compatible receiver equipment on Earth, and adequate knowledge of that equipment's operation.
Other types of knowledge arks might include genetic material. With the potential for widespread personal DNA sequencing becoming a reality, an individual might agree to store their genetic code in a digital or analog storage format which would enable later retrieval of that code. If a species was sequenced before extinction, its genome would remain available for study even in the case of extinction.