We of course don't know. But I think the claimed evidence is that bacterial life arrived quite early in Earth's history, perhaps a few hundred million years or

We of course don't know. But I think the claimed evidence is that bacterial life arrived quite early in Earth's history, perhaps a few hundred million years or less after there were permanent basins of water. So the assumption is that it arrived almost as soon as it possibly could (whereas intelligent life (us) took a few billion years longer to show up).