Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Salvage Rights (5 points): Destroy at least one boss alien.
Field Promotion (10 points): Earn at least one silver medal in any mission after The Awakening.
Death From Above (10 points): Fire the orbital laser.
Tower Expert (10 points): Build at least one of every tower type and available upgrade.
Flawless Victory (15 points): Earn at least one gold medal in any mission after The Awakening.
Nail Biter (15 points): Win a mission with the last remaining core less than 10 seconds away from the map exit.
Base Defender (20 points): Complete the Story mode in The Awakening campaign.
Planet Defender (20 points): Earn at least a silver medal on all Story mode missions in The Awakening campaign.
Exterminator (20 points): Destroy 1000 aliens.
Alien Tears (20 points): Earn at least a gold medal on all Story mode missions in The Awakening campaign.
Siege Breaker (25 points): Survive all 99 waves on any Grinder challenge mode.
Master Strategist (30 points): Earn a gold medal on at least 40 Story or Challenge mode missions in any campaign.