Call of Duty Ghosts: how to unlock Extinction mode
In Call of Duty Ghosts Extinction Mode, up to 4 players are placed in a suburban town for the purpose of drilling and destroying alien nests. Each round of the game you proceed to a nest, place the drill and defend it from several waves of xenomorphs, after which you move to the next nest. Every 4 destroyed nests meets a barrier of alien organic material that must be destroyed with the help of a helicopter: while this happens we must defend ourselves from another alien wave. However, Extraction mode is not available from the beginning of the game.
How to unlock Extinction mode
Don't worry, it's nothing impossible. To be able to play Extinction Mode with your friends, all you have to do is keep playing.
Playing single you will have to complete the first mission of the campaign called "Ghost Stories". At first it was thought it was necessary to complete the first 4 missions, but apparently you just need to complete the first at any difficulty level.
The same result can also be achieved playing online multiplayer: in this case, to unlock the extinction mode, just reach the Player level 5.
Consult the fact sheet Call of Duty Ghosts cheats and guides for other useful guides on this game.