When did life start? Here on Earth, about a billion years after the Earth formed. But that’s here on Earth. What about out in the universe somewhere? Well, Abraham Loeb has an interesting take on it. Right now, the Cosmic Microwave Background (CMB) is about 2.7 Kelvin. That’s 2.7 degrees above absolute zero. But it wasn’t always there. The CMB is leftover radiation from the Big Bang. As the universe expands, the energy gets spread out and the tempeature decreases, and now it’s just 2.7 Kelvin.
But, at some point in the past, it had to be around room temperature. Somewhere above the freezing point of water. That means that a rocky planet out in space, far from a star, would still be warm enough to support life.
These conditions existed when the universe was 15 million years old. That’s about 13 billion years ago.
OK. We don’t know that there was life then. But we know that the conditions could have been right for it.