Gaea's Cradle

If this card's activated ability produces mana and doesn't target, it's a mana ability. Mana abilities resolve immediately without using the stack — opponents can't respond to them. However, abilities that target (even if they produce mana) aren't mana abilities.

This card has a static ability that applies continuously as long as it's on the battlefield. There's no trigger or activation — the effect just exists. Removing the permanent is the only way to stop it.