I mean, the Great Oxygenation Event is ~2 billion years in the past, and the Cambrian Explosion is only half a billion years ago. If intelligent, space-faring aliens checked it out, there's a 75% chance they arrived while the most interesting thing on Earth was, well, I can't think of anything that wasn't "technically before the Cambrian but like, only by 50 million years". Fungi?

We should look for oxygen-rich atmospheres, but we need another signal before we jump in a rocketship and go looking for someone to talk to or eat.