Here is a thumbnail breakdown the most important factors each search engine considers, roughly laid-out in order of importance.
Google: Incoming Links, On-page SEO, Site Design Spiderability, User analytics, Outgoing links, Inclusion in other Google indexes, Document Histories
Yahoo: On-page SEO, Links and Link Patterns, Site Design, User analytics, Inclusion in other Yahoo indexes, Document Footprints
MSN: On-page SEO, Site Design and Structure and Sipderability
Ask: On-page SEO, Site Design, Site Structure and Spiderability
So, what could be the main aspects in 'document histories'?
1) How long has your website been online (Domain age)
2) The length of time a domain has been registered
3) website theme since beginning date to till
4) ?