Google has launched another compelling search option on its fast diversifying website. Google News Archive Search gives access to selected news archives that allow researchers to view historic events through contemporary reports.

The service includes links to newspaper and magazine archives (such as those of The Guardian and Time magazine) which make the majority of historic articles free to view, alongside links to pay-per-click reports from the US regional press (such as The Washington Post, Philadelphia Inquirer, New York Times) and key reference and news aggregators (including Factiva, LexisNexis, Thomson Gale and Highbeam Research).

Anurag Acharya, described as a "Distinguished Engineer" at Google, announced the new service on the Google Blog, saying: "This new feature can help you explore history through archives of news and other information sources. You can search for events, people and ideas, and see how they have been described over time."

Surprisingly, one of the major partners in this enterprise is Time magazine, a division of Google's search rival, AOL Time Warner. Time offers an online digital archive that features its iconic covers - all of them since 1923 - and most of its archived content, all of it freely accessible within a framework that displays current advertising.

Another striking innovation is a Show Timeline option, which categorises results according to their publication dates. Search on "Winston Churchill", for instance, and you'll get a chronological decade-by-decade outline of results, admittedly most of them contemporary reports from Time magazine.

It may be sketchy at most at this stage, and will only become truly invaluable to researchers when more digitised archives become available, but it clearly adds a new dimension to Google search results. According to one report, Google may have plans to integrate this feature, alongside book search results, in the main results page of standard search queries. Alongside initiatives to "weight" results towards increasingly influential social computing sites like Wikipedia, Google is attempting to make more relevant material available on the first results page of any given search.

Google is looking for ways to hold on to the lead it has gained over rivals Yahoo and MSN in the US. Two other players with networks of search sites - Ask and AOL Time Warner - are also starting to see a little growth again having been impacted by the Google juggernaut.

The latest monthly survey of US search engine market share by Comscore shows Google losing ground month on month (43.7% in July, down from 44.7% in June), while enjoying a significant 7.2% year-on-year increase.

For Google's rivals the midsummer month-on-month results suggest they may have reached the end of their downward trajectory - Yahoo sites climbed slightly from 28.5% to 28.8% (compared to 30.5% in July 05), while number 3 player Microsoft saw its share flatline at 12.8% (compared to 15.5% in July 05).