The origin of "ta"

Alright then I don't know about everyone else but "ta" as a short form of thank you is alive and well in my vocab. Language for me is practical, I don't know many big words and, while I can pull together a slick sentence when required, I am far from a mistress of the English language. Ironic given I am in communications. Every now and then I flip into kiwiana.....ta being one of those words that I flip off easily (well people are being helpful, what can you say?). The first time I got a quizical instant message back seeking to grasp what, exactly, I meant. A simple inquiry along the lines of, this is good, yes?
Today I flipped a "ta" (with an explanation that it was New Zealandish) to someone who works for me. She is new to the program so currently everything she is writing requires quite alot of back and forth while she learns both content and style/tone.....that sounds pompous, I don't mean it too......it's just part of what being in communications is all about!). So we are endlessly swapping emails and IMs all day (among the other endless emails and IMs I am getting; Kathy is away and I am learning what it is to have no immediate top cover) while she writes what is a relatively simple message - don't be fooled, these are the hardest. Finally I get to "ta" and explain it's kiwiana for thank you. Her flip back is the American version is "way to go dude". I am not sure is "ta" "way to go dude"?......made me laugh and at hour 10 in my day that was sufficient to make it all worthwhile! And to be honest, it was "way to go dude".......in the end we got there. At no point did I feel the need to just take over and do it myself (tempting but a. probably wouldn't have ended up reading as well as it did, b. not sustainable, I have 6 people who need do do their jobs so I can do mine, and c. there was a very lovely moment where I could tell she just felt proud of herself for hitting the mark.......). It was a long day in everyway but I think "ta" has become a benchmark; I am not sure I will ever get to "way to go dude" but I did get the sentiment. I am so back to being a corporate geek.