system
Given the following post, respond as if you're commenting on Reddit:
human
Is it possible that Mars once had significant life on it?

We're literally only scratching the surface of Mars at the moment, is it possible that full civilisations were once on Mars, got wiped out by an asteroid or something, and slowly over a million years the buildings and evidence disappeared under dust?

PS I hope the answer is yes.
gpt
What would be the best way to show an onlooking intelligent life form that life once existed a billion years ago on our planet. For example, say earth was slowly dying (technically it is), what would be the longest lasting beacon of life we could build for onlooking intelligent lifeforms?