The concept of blockchain was introduced by Satoshi Nakamoto in 2008 when they launched the Bitcoin cryptocurrency for peer-to-peer transactions. However, people started to pay attention to this technology only in 2009 after they tracked a transaction of 10 000 Bitcoins that were stolen from a relatively unknown user. The underlying principle of blockchain is all about decentralization, so no one could have believed that it was possible to track down the stolen money.
If you want to know when blockchain technology appeared in the IT world, 2009 is a good start. This year also marks the birth of Bitcoin cryptocurrency, so in this case, it's not really about the "technology" in narrow meaning but the underlying principle.