[Virginia-American]

I wasn't clear. I meant if I had RA's equipment on a planet circling Alpha Centauri, could I detect Earth's radio waves? On a planet around Vega? or whatever star.

Or if there were a duplicate of Earth around a particular star, could it be detected with our equipment?

Actually imaging Earth-like planets may someday be done with massive interferometers in orbit. I'd consider O₂ in the atmosphere a sign of life.

We can't forget that Earth is 4.5 billion years old, over half that time there were no eukaryotes, big animals date from the half a billion ya, and we've only been broadcasting radio for 100-odd years.

[longshadow]

Here's a link to one of RA's more technical explanations of how the distance over which one can detact a signal is calculated. You'd have to fill in values for the various factors and do the calculation to see what the answer would be. Heavy GEEK ALERT:

http://www.freerepublic.com/focus/f-news/1289285/posts?page=28#28