Which are the exact requirements for the "Destroyer of Worlds" achievement?

It seems to be picking up blocks what counts, so picking up 10 000 000 of them from the ground is all that is needed.

The magic number can be found in the achievements\achievements\itemsplanetblocks.achievement file (extracted from Starbound\assets\packed.pak)

{
  "name" : "planetblocks",

  "triggers" : [
    "item.category.block"
  ],
  "scripts" : [ "/achievements/achievement.lua" ],

  "stats" : [
    {
      "name" : "item.category.block",
      "op" : "atLeast",
      "value" : 10000000
    }
  ]
}

Looking in the Starbound\storage\player\statistics file there seems to be a counter for item.category.block.

Leveraging py-starbound by renaming the statistics file to statistics.player and running cli.py -g stats statistics.player to dump the file in a readable format and comparing the number before and after picking up some blocks from the ground in game it seems item.category.block counts any blocks picked up.

To verify I created a new character and loaded his blocks inventory up with 40k blocks:

And constructed a suicide pit at the beam down spot:

After 227 suicides and re-spawns I got the achievement. Since you pick up the 40k blocks you drop on death each time you jump in the lava pit, 250 suicides will get you 10 000 000 blocks picked up if you haven't played at all.

I found my way to do it is to block yourself in the teleporter spot of your ship (where you respawn) and type /suicide over and over with your inventory filled with blocks. It took me about 9 minutes to get 5 million blocks so I belive this to be the fastest way to get it.