The Three Families discovered the Blessing's presence by realising that the average lifespan of people living in Shanghai over the Blessing was the exact same as the global average human lifespan, and had been so throughout history. The Blessing was the focus of a morphic field matrix that encompassed all humankind, and the Families were able to alter it by introducing Jack's blood on both sides of the fissure. Jack speculated that the Blessing perceived this as an attack, which is why it was trying to keep everyone alive. As a mortal, Jack's blood was attracted to the Blessing. Introducing his mortal blood on both sides, via Jack himself and Rex Matheson, reversed the process. It was later sealed off by UNIT. (TV: The Gathering, The Blood Line)