CERN timelines, such as the one above, are made up of "events". Each event is a short description in the present tense of what happened on a particular day. Link to original documents and relevant source material. Include any relevant video, images or even audio. 

Note that the date must be precise to the day. If your event happened over a longer period of time, you'll need to frame the copy to hang onto a particular day.

For example, though Einstein spent years thinking and writing about his theories of general and special relativity, the scientific papers he wrote have specific publication dates. Use the publication dates to tie theories to given points in time.

The CMS detector took years to design and build, but the Technical Design report was presented to council at a specific meeting on a specific day. Use dates of meetings or presentations to tie a long design process to specific events.