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.
Many species vanished in five cataclysmic mass extinctions and today, 99.9 percent of all species that have existed on Earth are extinct. T he Ordovician-Silurian extinction occurred about 439 million years ago due to a drop in sea levels as glaciers formed followed by rising sea levels as glaciers melted.During this extinction 25 percent of marine families and 60 percent of marine genera (the classification above species) were lost.T he Late Devonian extinction took place somewhere around 364 million years ago. To this day its cause is unknown.uring this extinction 25 percent of marine families and 60 percent of marine genera (the classification above species) were lost. T he Late Devonian extinction took place somewhere around 364 million years ago.