Yellowstone caldera question?

In my geology class we learned about the Yellowstone supervolcano. My professor said that it erupts about once every 400,000 years and that the last eruption was 600,000 years ago. We also discussed possible consequences of it erupting now and everyone was saying that the whole world would be affected and that many plants and animals would die out. I became really concerned when I heard this and I was surprised that I was the only one. I am a little skeptical that a very small part of earth could affect the entire world, but still... After class I went on wikipedia and it says that the last eruption was 70,000 years ago. What date is correct? And if it is the former do we have anything to worry about?