Portal was the first Valve-developed game to be added to the OS X-compatible list of games available on the launch of the Steam client for Mac on May 12, 2010, supporting Steam Play, in which players that had bought the game either on a Macintosh or Windows computer could also play it on the alternate system.
1 Eurasian Pleistocene megafauna became extinct in roughly same time period despite having a much longer time to adapt to hunting pressure by humans. 2  However, the extinction of the Eurasian megafauna can be viewed as a result of a different process than that of the American megafauna.
3. PermianâTriassic extinction event (End Permian): This one occurred right about 251 million years ago. It is the largest extinction event that is currently known. It led to the extinction of â57% of all families, 83% of all genera and 90% to 96% of all species.rdovicianâSilurian extinction event (End Ordovician): It occurred about 450â440 million years ago. It actually consisted of two different events, in total they annihilated 27% of all families, 57% of all genera and 60% to 70% of all known species.