This is definitely a blockchain. My husband has been mining and adding to the blockchain, just like you would with any cryptocurrency. This just has the addition of having a content creation component. I think the hybrid mission of Steemit could actually make a difference in the world. Take a look at my husband's article about it. And I'm still hoping to see your p vs np one! :)

https://steemit.com/steemit/@melek/open-discourse-and-how-steemit-is-qualitatively-different-from-every-intellectual-society-that-proceeded-it