The bitcoin algorithm periodically adjusts the difficulty of mining a valid block hash in order to keep it around 10 mins per block on average. If, in the prev

The bitcoin algorithm periodically adjusts the difficulty of mining a valid block hash in order to keep it around 10 mins per block on average. If, in the previous 2016 blocks, the average block took less than ten minutes to mine then the difficulty increases and vice-versa. https://en.bitcoin.it/wiki/Difficulty https://en.bitcoin.it/wiki/Difficulty