What triggers age advances?

[WoundedKnight]

Still a liffle fuzzy on this. What triggers advance from one age to the next? I know you don't need all the techs to advance, but is there a certain number of total techs, or a certain number of terminal technologies, that you need in each age to open up the next age and make a new tech tree available?

Thanx,

WoundedKnight

 

[Exsanguination]

look at your science advisor screen (in-game). All the techs in each age WITHOUT a little circle with a line through must be researched to advance to the next era. All the ones WITH one are optional, and if you don't research them you will have the opporunity to at any time, in any era. However, usually these techs unlock valuable wonders or improvements.