The first layer consists of research reports, which are written by specialists and academics and published in peer-reviewed journals for their peers to read. Because these articles are specialized in scope and assume an advanced level of knowledge by the reader, research reports are the most difficult for the general reader to comprehend. They also provide the highest quality information available because they provide close observation, measurement, and description of carefully defined natural events, phenomena, or processes. Research reports are also known as "primary sources."
"Secondary sources" take primary sources as evidence and then evaluate, interpret, summarize, or discuss them for a variety of purposes. One such purpose may be to make the research accessible to a larger audience of interested non-scientists. Another may be to identify trends or to detect whether there is a proponderance of evidence that may lead to new theory or that will inform the direction of future research. Secondary sources are sometimes found in the preliminary pages of peer-reviewed journals (look at the rss feeds for Nature magazine in this LibGuide). They are easier for a non-specialist to understand than research articles and are a good way for non-scientists to become introduced to topics.
"Tertiary sources" derive from primary and secondary sources and are written to provide broad overviews of topics that may be found in encyclopedias and textbooks. These sources are ideal for early contacts with a topic because they describe the topic in general, provide context and background, and outline its organization.
Peer-review at Science Publications - science publishing in the real world. Note at the bottom of the page that peer-review instructions differ based on the type of article being reviewed, research articles, reports, review articles, etc.
Summarizing a Research Article - Although this article was written for psychology students, it provides helpful advice for reading a research article for the first time. "Allow enough time," and "read each section several times," is the kind of common-sense, reassuring help provided.