What are the "eras" of anime, and which shows defined them?

I want to be sure I've seen all the shows that marked a transition period into different eras of anime, and I don't want to miss any. This might be a little subjective.So far I'm under the impression that there's an era of anime that started with Astro Boy, an era that started with Mobile Suit Gundam, an era that started with Akira, then Neon Genesis Evangelion, then Fullmetal Alchemist. But I'm not sure about between or after those. Did K-On define an era? Or Code Geass? What are your thoughts? http://ift.tt/2aiP4a6