Historical Rules · 1 February 2010
Rule 702.81a
Official source text from the 1 February 2010 Rules release
Unearth is an activated ability that functions while the card with unearth is in a graveyard. "Unearth [cost]" means "[Cost]: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step. If it would leave the battlefield, exile it instead of putting it anywhere else. Activate this ability only any time you could cast a sorcery."