It is one of the synthesis matrices the Creators use when seeding a world.  Each synthesis matrix is used to achieve the Creators' goals.  For Azeroth, a subterranean being matrix was modified to create a being with increased durability with an affinity for deep region shaping; the Earthen are the product of this modification.$B$BAfter the Earthen had been put into service for the Creators, unforeseen anomalies were discovered that affected their synthesis matrix due to high-stress environments.