Approx. 1st time life could appear in universe?

[Feck]

So, we haven't nailed it down to one billion-year window yet?

Well, as the oldest stars yet observed are 13.2 billion years old.
So if some were maximum size at that time, and went supernova at one million years old, followed by another one million years later, and another soon after, you have 3rd generation stars 13,195 million years ago. Take another 500 million years for an Earth-like planet to cool, and life could start then.
That's my estimate. 12,695 years ago.

So where are they? Just thinking of the Fermi paradox. If life has been around for 12 billion years, we might expect to find a few beer bottles that the aliens threw out of the UFO window.

Space is Big ! and maybe they don't litter; like cosmic Wombles .

[Clinton Huxley]

So, we haven't nailed it down to one billion-year window yet?

Well, as the oldest stars yet observed are 13.2 billion years old.
So if some were maximum size at that time, and went supernova at one million years old, followed by another one million years later, and another soon after, you have 3rd generation stars 13,195 million years ago. Take another 500 million years for an Earth-like planet to cool, and life could start then.
That's my estimate. 12,695 years ago.

So where are they? Just thinking of the Fermi paradox. If life has been around for 12 billion years, we might expect to find a few beer bottles that the aliens threw out of the UFO window.

Space is Big ! and maybe they don't litter; like cosmic Wombles .

I read something that said instead of searching for radio signals from ET, we should be looking for their junk.

[mistermack]

So, we haven't nailed it down to one billion-year window yet?

Well, as the oldest stars yet observed are 13.2 billion years old.
So if some were maximum size at that time, and went supernova at one million years old, followed by another one million years later, and another soon after, you have 3rd generation stars 13,195 million years ago. Take another 500 million years for an Earth-like planet to cool, and life could start then.
That's my estimate. 12,695 years ago.

So where are they? Just thinking of the Fermi paradox. If life has been around for 12 billion years, we might expect to find a few beer bottles that the aliens threw out of the UFO window.

Aha! Gotcha.
I found a beer bottle only yesterday. And it had a picture of a star on it.

[Feck]

I think they have internal 'junk' that's what they are looking for with all those anal probes !

[Clinton Huxley]

I think they have internal 'junk' that's what they are looking for with all those anal probes !

A nanosecond after pressing submit, I realised what I'd done....

[mistermack]

Corse I meant 12,695 million years.

Here's the bottle I found. The first conclusive proof, from the planet Newcastle :

[Clinton Huxley]

Corse I meant 12,695 million years.

Here's the bottle I found. The first conclusive proof, from the planet Newcastle :

Ah, a relic of the star-spanning Jor - Dh'ee Empire!

[mistermack]

Corse I meant 12,695 million years.

Here's the bottle I found. The first conclusive proof, from the planet Newcastle :

Ah, a relic of the star-spanning Jor - Dh'ee Empire!

Yes, I've looked it up, and it's eight billion brown-years away. Probably not fit to drink now.

[Clinton Huxley]

Dude, it was never fit to drink. I've not touched the stuff since I was 18.

[mistermack]

Dude, it was never fit to drink. I've not touched the stuff since I was 18.

I have. There are some pubs where the beer is so shit, you have to drink bottled.
I don't know much about bottled beer, but NB is better than nothing.

[Xamonas Chegwé]

The main reason that iron needs to be present for life (anything like we know it) to evolve is nothing to do with its necessity in any biological process.

Without an iron core, the Earth would not possess a magnetic field strong enough to repel the solar wind and keep its atmosphere in place. Without an atmosphere, temperature fluctuations would be far more extreme and the seas would vaporise and also be lost.

We owe our relative climactic stability to our iron core.

[mistermack]

The main reason that iron needs to be present for life (anything like we know it) to evolve is nothing to do with its necessity in any biological process.

Without an iron core, the Earth would not possess a magnetic field strong enough to repel the solar wind and keep its atmosphere in place. Without an atmosphere, temperature fluctuations would be far more extreme and the seas would vaporise and also be lost.

We owe our relative climactic stability to our iron core.

That's true, but you could have a very different setup.
If we had no tilt, we wouldn't have the seasons. And if the rotation was much faster, the temperatures would have less time to climb and drop. So you could get temperature stability in different ways.
You could have liquid water on a planet or moon, because of tectonic activity, or an internal heat source.

Or, you could have a planet a lot farther from it's star than we are, but with a powerful internal heat source.
So the harmful rays are weaker, but liquid water and an atmosphere is still possible.

There are bound to be circumstances that we can't dream up, but are out there, with liquid water and radiant energy from a star.

[Xamonas Chegwé]

I was thinking more in terms of day/night than seasons. The temperature differential without an atmosphere would be extreme.

Any internal heat source would only have a finite lifespan and would diminish over time. So, while a form of primitive life may well be able to evolve on such a world, without a (reasonably) constant input of energy from a star, it would not last long.

I suppose that trapped liquid water (such as has been speculated on Europa) could support life - and that gravitational flexing from the orbit of a gas giant could introduce energy into the system. As you say, there are many trillions of worlds out there and there may well be some as yet undreamt of way that life has managed to evolve in the most unlikely places.

[Xamonas Chegwé]

I was thinking more in terms of day/night than seasons. The temperature differential without an atmosphere would be extreme.

Any internal heat source would only have a finite lifespan and would diminish over time. So, while a form of primitive life may well be able to evolve on such a world, without a (reasonably) constant input of energy from a star, it would not last long.

I suppose that trapped liquid water (such as has been speculated on Europa) could support life - and that gravitational flexing from the orbit of a gas giant could introduce energy into the system. As you say, there are many trillions of worlds out there and there may well be some as yet undreamt of way that life has managed to evolve in the most unlikely places.

[mistermack]

I've just been reading a bit about Venus in Wikipedia, and it is quite an amazing place.
Even though it doesn't have a magnetic field, and it's gravity is about the same as Earth's, it has about ninety three times as much atmosphere as the Earth. ( Even the hot temperatures and being closer to the Sun hasn't blown it away ).
It's not very clear on why so much atmosphere remains, it's mainly CO2 and nitrogen.

What's intriguing is that it's upper atmosphere 50 km up is actually similar in temperature and pressure to the conditions here on Earth, and is the closest conditions anywhere in the solar system to Earth conditions.
People could actually live on Venus, in the upper atmosphere.
If you built a vessel like one of the old airships, and filled it with breathable air, it would float about just like an airship, because breathable air is a less-dense lifting-gas on Venus.
So it would be possible to colonise it in that fashion. ( Theoretically ).