each block includes a "blank check" transaction crediting 50 bitcoins to an arbitrary address. every 2016 blocks, the clients look at the rate of block generati

each block includes a "blank check" transaction crediting 50 bitcoins to an arbitrary address. every 2016 blocks, the clients look at the rate of block generation and adjusts their difficulty expectation to target 1 block per 10 minutes. your chance of solving a block (and crediting yourself 50 bitcoins) is proportional to your hashing rate. by the way, a miner only has to control above 50% of the hashing power to monopolize bitcoin generation - they can then ignore other block solutions without their branch being orphaned.