These achievements are related to destroying any of the blocks in the game. Anything that you can destroy counts as a block. After finishing all other achievements, it will take you another 50 hours or more to smash a total of 500,000 blocks. If you are going to attempt this achievement, there are a few levels that work well.
Level 5-19: Use the three birds you are given to destroy the three large piles of miscellaneous blocks. I found hitting the bottom pile first, then the top, followed by a shot aimed towards the far right of the screen to clean up the mess was best. You can get around 40-60 blocks per attempt of the level, netting around 150 per minute. At this pace, it will take you around 55 hours to grind all 500,000 blocks.
Level 4-13: This level can also net you up to 80 blocks or so per attempt of the level. However, it is highly variable and a little trickier to make the shots necessary. The most important part is to hit the trees. They can be completely destroyed with one hit and contain around 15 blocks each. This outcome of this level is highly variable and you should probably just stick with the Level 5-19.