Primary sources are the "raw materials" of scholarship.  For your research project on your chosen scientific controversy, you'll likely need to identify scientific primary sources and historical (or humanities) primary sources.

Finding Primary Sources:

What you ultimately decide to use as primary source material is highly contextual and depends on both your topic and your approach.  Consultation with a librarian and/or your professor is highly recommended. That said, here are some places to get started:

• Use tertiary sources to identify primary sources.  You also can use the citations in secondary scholarly work to identify what primary sources (and other secondary sources!) the scholar was using.
• What did the key figures in your chosen scientific controversy write?  Do an author search in Primo to find their writings.
• See if scholars have curated a set of primary sources; for example, in What's the Matter? Readings in Physics, James Hicks and Donald Whitfield have curated and edited a set of primary sources (writings by scientists) that illustrate key debates in physics over the past century or so.

In the sciences, a primary source:

• is peer-reviewed;
• is published in a scientific journal;
• and contains first-hand reports of research presented by the person or team that did the research.

Primary scholarly references are the gold standard for your background research as a scientist. Secondary scholarly literature—review articles, books, encyclopedias, handbooks, etc.—are useful entry points, but shouldn't be used alone. Follow up on the citations you find in secondary sources to get to the primary scholarly references.

Scientific primary literature is peer reviewed, or refereed, before being published. This enhances the quality and validity of the work. In the peer-review process, two or three specialists in the field read and critically evaluate the work before it can be published. Peer review is a quality-control measure to ensure that the primary literature includes only high quality, valid scientific information. Primary authors may revise and resubmit articles to improve them. Secondary literature is less stringently reviewed.

In humanities disciplines, including history, a primary source:

• Is anything produced by humans during the time period under consideration:
  • Texts, whether published (books, articles, patents, transcripts) or unpublished (diaries, notes, manuscripts);
  • Imaginative work, such as paintings, music, movies, or novels;
  • Visual resources, such as photographs or newsreels;
  • Sound recordings, such as interviews;
  • Material culture, such as scientific instruments, clothing, or garbage dumps.

• Primo is a good starting point for trying to locate primary sources.
   
• For older materials, see if you can find a "scholarly edition" or "documentary history."  These are collections of carefully chosen primary source materials with introductions and annotations provided by scholars.
   
• If you have found a scientific primary source, but are having difficulty understanding it, try to see if you can find a summary in a subject encyclopedia.  For more recent scientific primary sources, you might try to see if a summary or overview has been published in Scientific American, a non-scholarly journal that attempts to translate science for a general audience.
   
• News databases (both current and historical)