Because of the information life cycle, where you look for information depends in large part on when it happened. 
For reasons of public interest, technology, and economics, information moves through society at a somewhat predictable 
pace.

Why?

A news team can film something happening, send it back to the station, edit it, package it, and then broadcast it on the news in a matter of hours. If the event is newsworthy, then newspapers and magazines can arrange to have coverage or commentary about the event appear in the next day’s, week’s, or month’s issue. It takes longer for something to appear in a scholarly journal because those sources publish less frequently and because the information therein typically includes in-depth analysis. Finally, books and encyclopedias take even longer to write, edit, and publish. The general rule is that the longer it takes for the source to appear, the more in-depth the coverage will be. Note, however, that encyclopedias provide general overviews, and therefore are meant only to introduce you to the topic.

A Caveat!

The internet extends the timeline. Webpages or blogs can be edited and/or uploaded hourly but may contain information from any point in the past or present. Even if the information is newly uploaded, it may be old information that reflects only what was known at the time of its creation. An excellent use for such sources is to provide social or historical context to your research.

What Your Research Process Might Look Like

If you have been given the task of writing a research paper about President George H.W. Bush’s efforts to convince the American public that the 1991 Iraq War was a worthwhile endeavor, you might consider consulting the following sources:

Preliminary Reading

Encyclopedia Britannica entries:
Iraq and the war of 1991
George Herbert Walker Bush
Saddam Hussein
Kuwait

An Internet Search:
(advertising OR marketing OR public relations) AND (Gulf War OR Iraq War 1991)

Deeper Reading

EBSCOHost and JSTOR searches for full-text, peer-reviewed journals:
(advertising OR marketing OR public relations) AND (Gulf War OR Iraq War 1991)

The Library’s Online Catalog:
Iraq War 1991 and mass media

Contextual Research

A YouTube.com search:
Desert Storm AND Gulf War 1991

Newspaper or Magazine Archives in Microfiche/Microfilm or online databases:
Scanning the dates October 1990 to February 1991 for examples of new stories, ads, and editorials to determine the “mood” of the time.

All of these sources come from different time periods and contain information from different points in the information life cycle. Understanding how they all fit together to for a complete picture is part of information literacy.