The Archive was a galactic library in the far future.
Abby and Zara found a copy of volume 36,379 of Kronos Vad's History of Earth, but from an alternate universe. It described an invasion of Earth by the Gomagog. They took it to Earth in the past as a warning, with the hope that it could prevent the invasion from happening in their own universe. (AUDIO: The Archive, Kronos Vad's History of Earth Vol. 36,379)