Previous intelligent civilisations on Earth? - NOT amateur radio

There was a post on Facebook earlier that got me thinking. 

The Earth is probably 4 billion years old and humans have maybe been around maybe 500000 years. What if intelligent civilisations existed in the distant past and then destroyed themselves without a trace? This is very unlikely as we would probably have found some evidence such as tool remains.

However, this could have occurred elsewhere in the solar system (Venus,Mars?) or on other planets in the universe.

Intelligent life "out there" - NOT amateur radio

As far as I am aware the SETI project has been looking for intelligent life in the universe for almost 60 years. As far as I know, nothing has been detected. Maybe our methods are flawed?

What seems probable, but not certain, is that "out there" somewhere intelligent life does exist. Even with pessimistic estimates there are 10s of intelligent civilisations in our galaxy. There are trillions of galaxies in the observable universe, so the probability of intelligent life existing somewhere goes up. They may be so far away that we cannot interact with them, but with time we may detect some of them.

All this makes me puzzled. All religions seem too small and too human-centric.  Life is a total mystery.

See https://www.nationalgeographic.com/science/article/how-many-alien-civilizations-are-out-there-new-galactic-survey-holds-clue .