1. A method for determining a particular document that initiated a topic of interest in a collection of documents, each of the documents having contents and a time it was created, comprising: ranking the documents in the collection based on the respective times that the documents were created; ranking the documents based on how similar their respective contents are to the topic of interest; ranking the documents based on originality of their respective contents; ranking the documents based on a type of source each respective document originated from; producing a composite ranking of the documents based on the time, the contents, the originality rankings, and the type of source; and determining the particular document that initiated the topic of interest from the composite ranking.
8. The method of claim 1 , wherein the originality ranking comprises determining if the documents include a reply indicator.