The news archive search is one of several new Google services

The web-based tool allows users to explore existing digitised newspaper articles spanning the last 200 years and more recent online content.

People using the search are shown results from both free and subscription-based news outlets.

Partners in the project include the websites of US newspaper the New York Times and the Guardian from the UK.

Other sources include news aggregators, websites which collect and display news stories from multiple sources.

"The goal here is to be able to explore history as it unfolded," said Anurag Acharya, an engineer at Google and one of the team behind the project.

"It's fascinating to see how people's attitudes and emotions have changed through time."

History lesson

The new service searches hundreds of different news sources to answer a user's query. The exact number of sources is confidential.

Results are presented in similar fashion to a Google News search, with "related" articles about the same event grouped together. Free and charged-for articles are displayed side by side.

The ability to browse this historical overview allows users to identify key time periods and get some sense of the flow of events

Anurag Acharya

Google's empire

With pages from commercial websites, the cost of viewing them is also shown. Google says search results are based on relevance, not partnerships with companies.

Users can also view articles using a timeline that displays key dates associated with a story.

So the first Moon landing would highlight 1969 as a key date, but also identify other years when lunar landings took place or when the topic was in the news.

"The ability to browse this historical overview allows users to identify key time periods and get some sense of the flow of events," said Mr Acharya.

The earliest known searchable story is, he said, from "somewhere in the mid-1700s" - considerably older than the current 30-day archive offered through Google News.

The service is accessed through the news archive website or the Google news page. It is also activated when it can provide relevant results to a user's search on google.com.

In this case, links to the most relevant historical news articles are displayed separately above the normal search results.

Historical challenge

The launch of the news archive search extends Google's influence over how the world's information is indexed, searched and accessed.

The way we access information is changing

According to online research firm Nielsen/NetRatings, more than 380 million people used the search engine every month in 2005.

The company is also expanding into areas other than search. In August it announced plans to offer consumers the chance to download and print classic novels free of charge.

"I'm strongly in favour of the democratisation of access to historical documents, but also cautious about how much information Google now controls," said Professor Roy Rosenzweig, a historian from the Center for History and New Media at George Mason University in the US.

He says that increasingly the model of how we access information and what information we have access to is changing, as public archives such as libraries are replaced by private companies. But, he says, he is "extremely excited" about Google's latest offering.

"As a scholar and historian I want as much information as possible, accessible to as many people as possible at the least cost, and the extent to which Google is doing that is compelling."

Google says it plans to launch the news archive search service on other international Google sites soon.