After the miner has successfully verified that all transaction in the block are valid, he must then compute a cryptographic hash. It is necessary for miners perform this computation in-order to prevent just anyone from being able to create blocks therefore secures the network against fraudulent blocks. Computing a cryptographic hash requires a large amount of computing power as hundreds of millions of calculations are needed to be performed each second. This process is known as proof-of-work. Once the miner successfully solves the hash, his block is then relayed to the network to be checked against the consensus rules. Once accepted, the block is then added to the blockchain network and the miner is rewarded with set amount of the cryptocurrency.
The supply of bitcoins grows by the process called “mining” bitcoins. The supply is expected to increase by 10% in 2014 after going up 11.11% last year. The rate of block creation is 6 per hour with each block worth 25 bitcoins (around 25k USD). If more mining power goes online and the block generation increases to 7 blocks per hour for example, the so called “mining difficulty” will go up until the 6 blocks per hour average is reaffirmed. On the other hand if miners generate less coins then the difficulty will go down making it easier to generate new coins. You can read more about the supply of bitcoins here.
By October 2009, the world’s first Bitcoin exchange was established. At the time, $1 was the equivalent of 1,309 Bitcoin. Considering how expensive Bitcoin is today, that was a real steal. Bitcoin traded at a fraction of a penny for quite some time. Things started changing in 2010; as the distribution of Bitcoin increased, the digital currency became inherently more valuable.