About 300,000 years ago something happened that was unlike anything in the previous few billion years, something that would have ever-expanding repercussions.
Stanley Kubrick presented his view of this moment in "2001: A Space Odyssey." An ape realizes the awesome potential of the animal bone he is holding in his hands. Hurled into the sky, the bone morphs into a space station.
Meanwhile, Pope John Paul II, in his 1996 Statement on Evolution, said the turning point was when God intervened and divinely injected the soul into the Neanderthals and prehumans. (Incidentally, this Statement is also where the Pope admitted that "evolution is more than a hypothesis.")