Stages of Galactic Intelligence

Imagine the history of the galaxy with respect to extraterrestrial intelligence. Very early there were only first generation stars, no heavy metals and therefore no possibility of life, much less intelligence. That's Stage One. In Stage Two planets with heavy metals form from the starstuff processed in the previous generation of stars, life arises and evolves, but It's quite some time before a technical intelligence developes. In Stage Three, radiotélescopes are invented, radio contact among...