Primary sources: documents of direct experience; formal or informal; formal examples usually peer reviewed.

Secondary sources: organize, distil, or review primary sources. Review articles are a type of secondary source that can be very useful for understanding and finding primary sources.

Tertiary sources: discovery tools for primary and secondary sources.

How to identify where your source fits into the ecosystem:

- identify its genre (journal article, patent, review article, etc)

- identify its medium of publication (the journal title, the name of the conference, the book series, etc)

- the content of the resource itself. In particular, how far removed is it from direct observation of its subject?

For examples of primary and secondary sources, see the Primary, Secondary, and Tertiary tab.

How do you tell whether the article you're looking at is primary or secondary? Listed below are examples of primary and secondary journal articles to help you gain understanding of what they look like. Compare the source you've found to these examples.

Primary sources:

• A research study: Escherichia coli removal in biochar-augmented biofilter: effect of infiltration rate, initial bacterial concentration, biochar particle size and presence of compost

Secondary sources:

• A review of multiple research studies to highlight the current state of knowledge on a topic: Ecological Risks of Shale Oil and Gas Development to Wildlife, Aquatic Resources and their Habitats
• A news article about science policy dealing with air pollution: White House teams with private sector on plan to reduce HFC emissions
• A monograph gathering, reviewing, and commenting on various aspects of a wide-ranging topic: Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution

Tertiary sources:

• Wikipedia article on greenhouse gas.