Forgive me if anyone else has already pointed this out and I'm late to the party...
At the end of Cold Blood, the Doctor defers the emergence of the Silurian race for 1000 years from 2020. When - earlier in the season - it's been established that humanity abandons planet Earth for the stars in the 29th century, leaving the earth behind to be obliterated in a solar firestorm.
Has this slipped the Doctor's mind? Does he hope that the crack will make history "rewritable" enough for all of this to somehow work out fine in the end? Or has he just administered the ultimate "screw you" to the Silurian race, Nasreen and Tony? ;)