Not liking this idea to be honest.
The problem with this card isn't the actual mechanic itself (we have no cards that give out a +attack bonus only unless you include Chaos Power, in which case the stats boosts are too random), but rather,
the element.
already has a card that increases a creature's HP significantly (especially for cards like Otyugh and Lava Golem, where various synergies emerge), and if you gave earth another card to boost up attack... well...
I think that this type of offensive boost should belong to something in fire or even air. Earth already has powerful defenses and cards that match well with it. This would push the element overboard (especially since
both of the cards' costs are very cheap)...