I do not claim to know everything. If you make a logical and objective debate with canon evidence that I find convincing enough I will change this. Assumptions: I'm going to ignore the 3 Tier/Gameinformer timeline because Portal 2 has proved almost all of it wrong anyway. I will also be assuming that GlaDOS take over the Aperture Labs shortly before the Black Mesa Incident, which is why no rescue or investigation occurred or at least succeeded. I've heard that this has been official confirmed by Erik has confirmed this though I haven't seen the confirmation myself. 1940s – Cave Johnson uses his shower curtain money to buy a disused salt mine in Michigan and builds the first enrichment centre. 1940s and 1950s – Aperture Science develops first portal device. Test participants are astronauts, Olympians and the best of the best. Receives runner up award from Department of Defence behind Black Mesa. 1970s – Aperture falling on hard times pays bums and hobos $60 to perform tests. Also possibly the timeframe in which the Borealis test vessel was constructed and vansihed. 1980s – Aperture begins forcing staff to act as test subjects. Also (judging from the banner they use) the beginning of Aperture holding Bring Your Daughter to Work Days. Cave Johnson dying of lunar dust/conversion gel poisoning orders the scientists to work on the copying of a human mind into a computer. 1990s - 200X – Aperture scientists continue working on the Genetic Lifeform and Disk Operating System and Caroline's mind is copied/transferred into it. It attempts to kill everyone in the facility every time they turn it on. After it attempts to flood the Enrichment Centre with a deadly neurotoxin they install a morality core to stop it flooding the Enrichment Centre with a deadly neurotoxin. March 200X – The Hazardous Environment Combat Unit is trained for a mission to the Black Mesa Research Facility. They are not told the nature of the mission. May 5th to 15th 200X – Gordon Freeman begins his employment at the Black Mesa Research Facility. Unknown date* 200X – Other than some hostility against cats, GLaDOS appears to have calmed down. They decide to have an official unveiling at the Bring Your Daughter to Work Day. GLaDOS takes over the facility and captures or kills all of the staff and the daughters, including Chell. Shortly afterwards the Black Mesa Incident occurs, prevent rescue or investigation. *Possibly December judging from the in-game calenders in Half-Life. 2010s - 2020s – The events of Portal occur. 2010s or 2020s – The events of Half-Life 2 and Episodes occur. Years later – Portal 2 occurs.