neufer wrote:Ann wrote:I can't help noting that no one here has so far commented on my claim that we have reason to think that the Earth is rare. Personally I believe that the Earth is like a lottery winner, which, just out of pure coincidence, happened to win all the necessary characteristics that work together to make a planet very suitable for life. I also think that this "habitable planet lottery" is a very big lottery, and that there are few winners.
The momentum of discoveries is
ALL going in the direction of life being abundant in the universe:
- 1) the radio telescope discovery of complex hydrocarbons in space
2) the Miller–Urey creation of 22 amino acids "in a test tube"
3) the discovery of the simplicity of DNA replication
4) the discovery of prokaryotes 700 million years after the formation of the Earth
5) the discovery of prokaryotes both deep below the ocean & under the earth
6) the discovery of more than 100 billion galaxies in the observable universe
7) the discovery of earth-like planets around other suns
We also have clear evidence that parasites, disease & catastrophes
ALL help to speed up the evolution of any life once formed. In fact the development of eukaryotes 2 to 3 billion years ago was probably a direct result of prokaryotes and their parasites benefiting from mutual symbiosis.
Can Ann give even ONE example of any discovery that suggests that life might somehow be rare in the universe?
Thanks for giving me a list of factors to reply to, neufer! :
![:thumbsup:](//cdn.jsdelivr.net/gh/twitter/twemoji@latest/assets/svg/1f44d.svg)
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Let me start by commenting on your list fist:
1) Being a non-religious person, I of course believe that the necessary building blocks for life can be found naturally in space. I do believe, however, that it takes very, very special conditions to actually put those building blocks together. I find it encouraging that complex hydrocarbons have been found in space. That means I am right that many of the building blocks for life are indeed found in space, and in the few cases where all other conditions are right those building block can be put together to form life on other planets, too.
2) When I was a kid and heard about the Miller–Urey creation of 22 amino acids "in a test tube", when I was still trying very hard to be a religious person, I was shocked. I agree that the experiment is hugely interesting, and it gives us very valuable clues about the formation of life on our planet. So, yes, I truly believe that life can be created through natural processes. However, what Miller-Urey created wasn't life. What does it take to make life out of those amino acids? Probably very favorable conditions.
3) It's a good thing that DNA replication is simple. Creating the DNA helix in the first place seems harder, so I believe that complex hydrocarbons have to "cook" for quite a while under very favorable conditions for DNA to come into existence. I may be wrong about that. If DNA can credibly be found either in space or on a celestial body away from space, where it can't have been put directly by humans, then I will have to rethink my belief that life is rare in the universe.
4) It's impressive that prokaryotes existed on the Earth only 700 million years after the formation of the planet. In my opinion, this means not only that life can be formed through natural processes, but also that conditions were favorable on the Earth extremely early on. How were conditions favorable on the young Earth? Well, 700 million years after its formation the Earth may have had an almost planet-covering ocean due to bombardment by water-rich comets. The Earth had a rich source of internal heat, and there must have been many parts on the bottom of the ocean where heat vents let out a complex hydrocarbon soup into the water. Also, the Earth still had its all-but-circular orbit at a suitable distance from a comparatively "tame" Sun, which wasn't given to huge outbursts. If early Mars had an ocean at this time, too, which it may have had, then the Sun can't have had the kind of outbursts that would boil the oceans off of its terrestrial planets.
5) It is interesting that prokaryotes have been found deep under the oceans and under the earth. I think I'm giving in here, neufer. It is a distinct possibility that life may exist deep in the interior of many extraterrestrial planets. But if life only exists under the surface of those worlds, how will we ever know that it is there?
6) The discovery of more than 100 billion galaxies in the observable universe? So, the tally is 100 billion now? Last I heard, it was only 40 billion.
![Mr. Green :mrgreen:](./images/smilies/icon_mrgreen.gif)
Joking aside, neufer, you may have noticed that I refuse to say that there is
no extraterrestrial life in the universe. And the reason why I will never say that is precisely because the number of probable planets out there is so... "overwhelming" isn't the word for it, but you know what I mean. However, neufer. Like I said, my point is not that there is
no other life in the universe. Suppose there is, on average, exactly one planet in every galaxy that has life on it. Assuming that there are 100 billion galaxies in the universe, and disregarding questions of exactly "when" that life actually exist(s)/(ed) in relation to us, 100 billion planets with life on them isn't bad. But if the nearest planet with life on it is in the Large Magellanic Cloud, how are we supposed to find it?
7) The discovery of earth-like planets around other suns? I beg to differ. A few
earth-sized planets have been found around other suns, yes. So far, we have no reason whatsoever to believe that those planets are the least bit "Earth-like" in such a way that they can support life.
So, neufer, here is my list of things that,
when put together, makes the Earth habitable:
- 1) a metal-rich Sun of spectral class G2V, hot enough to save the Earth from a bound rotation
2) a Sun with a slow rotation, a benign magnetic field and few if any truly large outbursts
3) a single Sun
4) a solar system dominated by planets in fairly circular orbits, a Jupiter at a safe distance from us and a Saturn at a safe distance from Jupiter, all contributing to a "calm" and remarkably "stable" solar system
5) the Earth at a suitable distance from the Sun
6) an almost circular orbit for the Earth
7) the fact that the Earth is the most massive and dense of the terrestrial planets, with an iron core, a fairly strong magnetic field and a lot of internal heat
8) the fact that the Earth's magnetic field protects its atmosphere
9) the fact that the Earth has probably cooled at more or less the same rate as the Sun has grown brighter
10) the fact that the Earth probably formed at a distance from the Sun where the young Earth could not be born with a water supply, but that it got that water supply from a bombardment of comets
11) The fact that the comets likely brought nitrogen to the Earth which could form the bulk of the Earth's atmosphere
12) the fact that the Earth didn't get a runaway greenhouse effect from the CO2 it received, since the CO2 was mostly incorporated into the Earth's rocks
13) the fact that the Earth's internal heat has given it plate tectonics, which recycle a lot of life-friendly substances of the soil of the Earth
14) the fact that the Earth's temperature and atmosphere protects its liquid oceans and gives the Earth a precipitation cycle
15) the fact that the Earth's Moon, which may be a rest product of the celestial body that gave the Earth its massive core in the first place, stabilizes the Earth's rotational axis
16) the happy coincidence that some of the Earth's simple life forms started feeding themselves through photosynhesis, thereby releasing the O2 into the atmosphere that large energy-hungry organisms needed to survive
17) the fact that O2-breathing large creatures made CO2 as a rest product, thereby allowing the CO2 - O2 - CO2 cycle to go on
18) the fact that the O2 released into the atmosphere turned into oxygen compounds high up in the atmosphere which protect life on Earth from the Sun's ultraviolet light
I'm sure there are more things that ought to be put on this list. Such as, isn't it a happy coincidence that the Sun was likely born in a massive cluster of stars whose birth may have been triggered by a nearby supernova, and yet the Sun managed to escape the chaos of that cluster, get rid of any stellar companions and produce a family of planets in mostly near-circular orbits?
We know so little of the planets we have found around other stars. One thing is clear, however, and that is that chaotic orbits hostile to life seem to be very common out there. What will we find when we learn more about these planets? That apart from their orbits, they are so much like the Earth? That is not what I think, anyway.
Ann