Getting a Phd abroad: is there any chance?
Getting a Phd [outside of Greece]: is there any chance?


TL;DR: Yes


  I think i have built a pretty good CV for my level (and young age) with good grades, numerous poster presentations and 4 peer reviewed publications in well known journals in my field. 


Many universities will accept PhD students without any publications, so - with 4 peer reviewed publications - you seem like a good candidate.* You don't say how good your grades are, PhD students will typically be amongst the top of their class.

*I cannot answer specifically for  Earth Sciences.


  Is it possible to find a PhD in a prestigious University [outside of Greece], based
  on a good CV with degrees (Bsc, Msc) from Greek University?


Yes. You mention, during the last couple of months i am trying to find a PhD opportunity, has your search been unsuccessful? If so, why?