Google is now providing (sometimes!) a set of 3 “In-Depth” articles linked in at the bottom of the SERP. These articles are judged to be “in-depth” by a ranking algorithm that looks at what the article is “about” and judges whether or not it’s of sufficient length (and depth) to be potentially interesting to a searcher. Here's an example of 3 in-depth articles at the bottom of the search for [ global warming ]
And another example of 3 in-depth articles for the search [ cloud computing ]
Some of the judgment about the “in-depth-ness” comes from the way the article is marked up the publisher. (See webmaster notes below.)
Of course, as always, the content has to be fairly high quality. (Rants and screeds don’t make the grade.) Quality of writing, depth of coverage (and a good, nicely crawable image) all help make these articles accessible.
At this point, most of the in-depth articles from reasonably trusted sources such as NPR, NYTimes, Forbes, Atlantic, Nature, and so on.
This feature has just recently rolled out, so the triggering (that is, when you get the articles at the bottom of the SERP) is a little inconsistent.
For instance, some queries trigger, while others don't:
Not triggering: UC Berkeley, John Brown (abolitionist) , MOOC, information visualization, symphony, computer science, Stanford, UC Berkeley, diabetes, LDL, HDL
Triggers: San Diego, censorship, Los Angeles, cholesterol, ALS, genetic testing, Yale, Harvard, Woody Harrelson, Hunger Games, economics, biology
Of course, this will change over time as more articles are scanned and indexed as “in-depth” on a given search topic.
Note that sometimes you have to be a little specific to find these in-depth recommendations. For instance, the query [ SAT ] doesn’t trigger, but [ SAT test ] does.
And, as always, just because the articles are “in-depth” doesn’t absolve you of the responsibility to read skeptically and fact-check. These recommendations are just that—recommendations of longer-form articles that you, the searcher on that topic, might find interesting.
For webmasters: Be sure to include tags for: Headline, AlternativeHeadline, Image, Description, DatePublished, ArticleBody
Consider implementing an indexable pagination schema (by adding in link tags for rel=next/rel=prev).
See: https://support.google.com/webmasters/answer/3280182 for guidance about how to mark up YOUR articles so they’d be considered for inclusion.