This series' cards sound good enough to be rares (:
I think Graveyard is a field card too?
Imma keep an eye on this XD
Not in the sense GG means, because boneyard doesn't equally affect both players.
For Death I think of something like a diseased Bog, each time something dies both players gain 1 poision
For Time I'm thinking a slowing effect, like it casts silence on both players every other round, or sundials every other round or (for sheer quanta generation) both.
And since we don't have any direct creature regeneration skills, for life or light I would suggest all creatures get healed 1 or 2 each round.
And finally (my least realistic) for earth or gravity, creatures can't attack opponents directly if they have creatures on the field. If this is the case, they each attack a random creature.
Thats all for now, take what you will.