There seems to be some debate over what triggers the quests given by the Earthen Guardian, and what they lead to. I looked into this, and I believe the are triggered as follows:
Return to the Heart - linked to first minor boost; serves as a breadcrumb for A Fresh Trauma
Back to the Chamber - linked to second minor boost; serves as a breadcrumb for An Old Scar
Unlocking the Power - linked to third minor boost; serves as a breadcrumb for A Bolt from the Blue
My reasoning for this is that there are three breadcrumb quests. The Heart forge unlocks the main slot, and there are three minor slots to unlock. The first becomes available soon after likely around the position of the first slot. The second has been stated to unlock at 65, the location of the second minor boost slot. The third has been said to unlock as 75, but the final slot is at 80 so there may be some confusion, or the unlocks may happen the slot before the minor boosts.
If your Heart of Azeroth is already higher level than stated for these quests, the second and third quests are not offered. If anyone can confirm or disprove this feel free to do so.
EDIT - Return to the Heart is the first quest, Unlocking the Power is the second, so Back to the Chamber must be the last. Pretty sure these are unlocked when you unlock each new minor trait. My main unlocked them all at once coz he was already maxed, and didn't did the other 2 breadcrumbs. My alt has had them all so far. The vreadcrumbs will unlock even if you don't do the chains this way