1492, hands down, far and away more important than any of the other years mentioned. The discovery of the Americas utterly and totally changed the course of human history in a way no other event even comes close to having done.
Not as far as Australian Abrogines and the Maori were concerned.
Oh wait, they weren't humans, were they?
Alternatively, what about in 8xx when Leif Ericsson or whoever it was landed on Newfoundland?
Or why wouldn't the discovery of the sea route to India by Henry the Navigator qualify? That changed the whole economic picture of the world as Europe had access to spices without the dirty middlemen.
It's just plain stupid to try to choose a year which was pivotal in human history simply because what is important to some cultures really didn't matter to others.
Otherwise, I can say the unification of China in 223 BC utterly and totally changed the course of human history in a way no other event even comes close to having done. Why? Because instead of being fragmented like Europe and developing under ridiculous competition, China turned out to be a centralised state which strengthened and weakened according to whatever was in power. Thus leading to potentially different socio-politics when Europeans arrived in force in the 19th century.
Obviously, this argument is easy to shoot down - but it's exactly the same as the 1492 argument.
This topic is seriously Gavin Menzies territory. Which is why 1421 should be the most important year in the world.
Or 1500 when Zheng He discovered the South Pole.