Satoshi Nakamoto proposes a solution that begins with a timestamp server. A timestamp server takes a hash of a block of items to be timestamped and widely publishes the hash, such as in a newspaper or Usenet post. The timestamp proves that the data must have existed at the time, obviously, in order to get into the hash. Each timestamp includes the previous timestamp in its hash, forming a chain, with each additional timestamp reinforcing the ones before it. 
This solution is proposed on October 31, 2008 by Satoshi Nakamoto.