Thanks, suggestion #3 ( hope it fulfills all feedback ).

"The block chain provides Bitcoin's public ledger, a timestamped record of all confirmed transactions. This system is used to protect against double spending and modification of previous transaction records, using proofs of work verified by the peer-to-peer network to maintain a global consensus."

It seems important to me to mention the "consensus" as one of the main function of the block chain, since it's actually what allows the security features mentioned above on a P2P network.