Ancient Tech Found on Venus. Thoughts...

It was stated that Ancient Tech was found on Venus, and it is what helped our Golden Age along. This tech below Venus surface pre dated humanity. So I'm wandering who or what was on Venus(thriving perhaps) and when, before it was abandoned and the Traveler eventually lead us to it. I'm sure the Vex are tied to this somehow, I but really want to know how it got there. Leads me to believe that we haven't always been the only life in our solar system. Where did they go? Has this happened before?