Popular Sources are meant for popular consumption. They may summarize more in-depth scholarly research and studies for a general audience, leaving out nuance, details, and expertise. These sources may or may not have links leading back to the original scholarly sources that they cite. News sites fall under this category, although their investigative reporting may blur the lines by sometimes creating original research.
Author: not an expert in the subject
Audience: general
Original research or work: usually not, unless it's a journalist doing investigative reporting
Detailed: no
Sources cited: links may be included
Good for: a general overview, easy readability
Example: an article in the Colorado Sun about scientists naming new lichens after musical groups. The title: "Colorado Lichenologists Name Discoveries after Indigo Girls bring Colorado 'closer to fine'" (note: "closer to fine" is a famous lyric by the Indigo Girls). This popular source is annotated below, helping you to understand why it would be categorized as "popular" instead of "scholarly".
Scholarly sources are written by experts who have probably published several times in their area of knowledge. They provide in-depth explanation on a particular subject, usually their own academic research, with lots of detail. Scholarly works that appear in journals are often peer-reviewed (evaluated by other experts) and must cite and provide information on their sources, which you can follow up on. Sources like these are easily found in the Kiefer Library's many databases.
Author: expert
Audience: other experts
Original research or work: yes
Detailed: yes
Sources cited: yes
Good for: in-depth understanding
Example: An academic paper written by the scientists mentioned in the above article. The title: "Most Lichens are Rare, and Degree of Rarity is Mediated by Lichen Traits and Biotic Partners". The example scholarly source is annotated below, helping you to understand the hallmarks of an academic paper.
Both popular and scholarly sources have their place in research and writing your paper. Your professor may require several scholarly sources or they may require none, so be sure to read your assignment sheet thoroughly to find out.