Marvel has quite a few ranks that go to thors power level and beyond. I'm wondering though if there has ever been any indication what rank would be needed damagewise in order to destroy planets (as Galactus does).
Class 3000. But it is possible to use a Class 1000 attribute/rank power, and by pushing into Class 3000, to destroy a Planet.
In theory, if you are at Unearthly and Above, you have the theoretical power to target planets, As the Silver Surfer did, although its questionable whether you would get to skip some of the steps of Shift X, Y, and Z.
A Shift z (500) Could do it, going to 1000 and then 3000 with two steps up.
Class 3000 was the level for Celestials and Galactus, although Class 1000 was used for some other abilities. Class 1000 is also a default for Nuclear Attacks.
Universal Attacks are class 5000 and Beyonder. Death, Eternity, etc. Class 5000, Galactus High Evolutionary and Celestials Peak at Class 3000 and hurl planets. Class 1000 is wolverine's skeleton, nukes, and typical cosmic and reality bending characters at domestic, rather than intergalactic levels.
Anything beyond Unearthly could seriously damage a planet, depending on the plot. In comics, characters of really high power (Unearthly and above) will do such things depending on the story. Silver Surfer/ Firelord/ Thor destroying a planet is "acceptable" and "makes sense". While Hulk doing the same thing would not look right.
Mr Fantastic or Dr Doom, both of which are not uber-powered characters, could create device that might destroy the world (and IIRC did so more than once).
So it depends on who is doing the destruction and how.
Since you did not specify the situation, I assume that you are imagining a Galactus-like character showing up and destroying the earth. Anyone with a CL1000+ could do it in a simple swoop without people batting an eye.