If you are in Earth stance is an enemy allowed to spend the two opportunity to crit you or is that just for kata and other skills. Technically it is still spending the opportunity to target you which earth is supposed to prevent, but I could see how it could be considered differently.

Earth stance does prevent your opponent from spending opportunities to inflict a critical strike. It applies to all Attack action checks and all Scheme action checks. They cannot spend opportunities to inflict critical strikes or conditions.

It doesn't block strife, increased critical severity spends (if the hit would do a crit anyway), nor penalties to hit next turn.

Note also: it doesn't prevent crits by hitting you while incapacitated, nor those specified in the core success of the technique, such as Jade Strike. (but if a PC is subject to Jade Strike working on them, something has gone seriously wrong... )