I agree with this, though I believe it's older than 15,000-20,000 years. I would say 150,000 - 200,000 years and we saw some 'incredible' advances. Not Iphones and the internet, but more bronze age, like you suggest. The great flood events that all religions talk about, were the original 'homo sapiens' that were wiped out, with the exception of a few people, who had to start again.
Life outside of Earth is proven. The theory of Panspermia, is the most widely recognised theory of how life arrived on Earth. If Life arrived here, then it originated elsewhere.