Life on other planets, are we looking at the wrong planets?

[Fast77]

Scientists are looking for Earth like planets/bodies to find life on other planets/bodies, somewhere that is warm enough that liquid water can exist, and somewhere with basic organic molecules. Here's where I have a concern, in the 4 billion years of Earth's life, to our knowledge life had only emerged once(about 3.5 billion years ago). Since Earth itself is the most Earth like thing(obviously) how is it that we have not found life that had a different emergence. Does the Earth maybe not have the best conditions for new life to emerge? I just think there should have been more then 1 root to all the living things that exist, or has existed, given that we believe Earth has the prime condition for life. Maybe we're wrong about what is needed to create life?

 

[mfb]

I'll see if there is a forum that fits better than astronomy.

Since Earth itself is the most Earth like thing(obviously) how is it that we have not found life that had a different emergence.

Established life could have out-competed every new approach of life. It is possible that life could have developed multiple times but existing life was simply better adapted already. The first cells were probably slow, fragile, and not very flexible. Current life would simply eat something like that if it has anything of nutritional value.
It is also possible that the emergence of life is extremely unlikely, happening on average just once per 10^whatever habitable planets.

Does the Earth maybe not have the best conditions for new life to emerge?

A sample size of 1 for Earth might sound small, but outside Earth our sample size is even smaller (0). There is no indication that different conditions would be more favorable for life.

 

[jim mcnamara]

Thread moved to Biology.

 

[jim mcnamara]

Quick points:
1. your statement is a good one in most ways, but it would have been improved with a little searching on the internet, so you would have seen #2.
2. Exobiologists are very aware of this problem. The issue is that you cannot establish that hypothesis without data.
3. There are life forms on Earth that have very different biosynthetic pathways - like methanogenic bacteria.
https://en.wikipedia.org/wiki/Methanogen -- no "potty humor" please.

 

[Ygggdrasil]

The fact that there all extant life derives from a single origin of life does not necessarily mean that there was only one independent origin of life. As others have mentioned, these different forms of life would have been in competition and maybe the common ancestor of all extant life out-competed all other forms from different origins of life (after all, it is estimated that over 99.9% of species that have ever existed on Earth are extinct). Mathematical arguments have been made that it is likely that there were multiple independent origins of life on Earth, though no experimental or observational evidence of these independent origins exist. The fact that life arose on Earth relatively soon after conditions on Earth became amenable to life would also suggest that abiogenesis is not a very rare event.

In terms of astrobiology, one of the advantages of looking for Earth-like planets is that we have some idea of what life on Earth-like planets should look like and what signs we should be looking for. For very different forms of life, it is unclear how we might go about looking for signs of these life-forms with unknown biochemistry.

 

[mfb]

The fact that life arose on Earth relatively soon after conditions on Earth became amenable to life would also suggest that abiogenesis is not a very rare event.

Much later and we wouldn't be around to discuss this question. Complex life will struggle within a billion years, assuming no large-scale artificial terraforming.

Another thing to keep in mind: The history is not "a cell formed, and then all its descendants formed the different species". The last universal common ancestor (LUCA) lived long after the first cell. It had the full RNA to protein transcription mechanism already, and probably DNA as well. This LUCA was so successful that its descendants replaced everything that had evolved in parallel.

Horizontal gene transfer can make this a bit more complicated, but let's ignore it here.[/size]

 

[Bruce Zerr]

I have something to add:

Quote ..."In terms of astrobiology, one of the advantages of looking for Earth-like planets is that we have some idea of what life on Earth-like planets should look like and what signs we should be looking for."
- - - - - - - - - - - - - - - -
Take a close look at the underlined section - in the quote above. There's an assumption here, about Earth-like planets, that needs to be explored further.

I made an interesting discovery about two weeks ago - that appears may directly impact our ideas of which exoplanets are going to have either life, or be inhabitable (by us?). It may really expand our ideas on what a habitable planet can be like.

to 701 metres (-2,300 ft) Comex Hydra X (Hydra 10) simulated dive in an onshore hyperbaric chamber by Theo Mavrostomos on 20 November
1992.[16][17][18]

https://en.wikipedia.org/wiki/Hydreliox << Link added by Mentor with OP's help >>

I found this bit of information on Wikipedia - researching deep diving gases. Following links back to their source, discovered that this was a dry, simulation in a large onshore hyperbaric chamber. They increased the pressure slowly, in small stages - but it took 2-3 weeks to get to depth. There they kept the pressure on their people steady for a further 3 weeks. (I'm calculating the final pressure was right at or just below 1,000 psi., or almost 68 bar.) Then they started slowly to decrease the pressure in stages over a further 2-3 weeks - back to atmospheric.

Now the deepest gas mixture they were breathing for three weeks - was very close to an equal mixture of Hydrogen and Helium, plus 0.8% Oxygen. You can breath this gas mixture, even though it appears to have too little oxygen in it - because of the Law of Partial Pressures. My calculations indicate that at depth, your body would believe that it was breathing the equivalent of over 50% oxygen. Also, it's highly likely that this total gas mixture of H2/He/O2 is outside the Hydrogen/Oxygen explosive limit envelope - so it neither burns or explodes.

So, the point that I am making is - that we had people breathing a Hydrogen/Helium atmosphere gas mixture at 67 atmospheres pressure for three weeks. This gas mixture is also very similar in composition and pressure - to what would be found for Uranus, Neptune, or Super Earths. Also, since the pressure outside your habitat would be exactly the same as inside - one would need to build no special habitat. A regular quonset hut would probably suffice.

Now one would need to have an air handling system. One would probably need to have some sort of air filtration system - to remove some of the trace gases and/or hydrocarbons. If the Super Earth has fresh water and ocean - just add algae and sea weeds - to work on getting your 0.8% Oxygen.

 

[Ophiolite]

Here's where I have a concern, in the 4 billion years of Earth's life, to our knowledge life had only emerged once(about 3.5 billion years ago). Since Earth itself is the most Earth like thing(obviously) how is it that we have not found life that had a different emergence. Does the Earth maybe not have the best conditions for new life to emerge? I just think there should have been more then 1 root to all the living things that exist, or has existed, given that we believe Earth has the prime condition for life. Maybe we're wrong about what is needed to create life?

As long ago as1983, Raup and Valentine postulated "as many as ten independent origins of life", noting in their abstract:

There is some indication that life may have originated readily under primitive Earth conditions. If there were multiple origins of life, the result could have been a polyphyletic biota today. Using simple stochastic models for diversification and extinction,- we conclude: (i) the probability of survival of life is low unless there are multiple origins, and (ii) given survival of life and given as many as 10 independent origins of life, the odds are that all but one would have gone extinct, yielding the monophyletic biota we have now. The fact of the survival of our particular form of life does not imply that it was unique or superior.

D.M.Raup and J.W.Valentine Multiple Origins of Life Proc.Natl. Acad.Sci USA Vol. 80; pp.2981-2984, May 1983

 

[mfb]

@Bruce Zerr: That gas composition is not in a chemical equilibrium, you won’t find it naturally anywhere without life. Gas planets are lacking a surface to live on, you would need floating habitats, a constant conversion of water to hydrogen and oxygen, and you would have to defend against storms.

 

[Bruce Zerr]

You are correct. The gas composition, with 0.8% Oxygen, is not in chemical equilibrium. You're also right in that you won't find this, or similar gas mixtures, occurring naturally, without the presence of life.

Can you help me understand your next sentence better - "Gas planets are lacking a surface to live on."? So far I have not run across any papers discussing the solid/liquid/gas interface of a Super Earth planet. If you can, would you identify one or two papers that are applicable you know of. I was just hoping, (making an educated assumption), that 67-atmospheres of pressure around 70-degrees F - was below the critical Tc, Pc, Vc point on these three gases - above which strange things happen.

What can you tell me about storms - on a Super Earth Exoplanet, with a H2/He/O2 atmosphere?

When the Russians landed on Venus, as I remember they measured a CO2-atmosphere, at 100-atmospheres of pressure. They also measured a light breeze blowing - at only a couple miles-per-hour ... but because of the thick, dense atmosphere, the wind struck the lander with the power comparable to a large ocean wave hitting a beach. It 'flipped' the rover.

So, on a comparable note, a Super Earth with an atmospheric pressure less than or equal to 67-atmospheres - will be susceptible to a similar situation happening to any habitat.

You mentioned defending against storms.

Here's what I know. I can't visualize a real storm, other than a dust storm, on such a planet. Because of the great difference in the atomic weight of an Oxygen molecule (32-amu.) vs. Hydrogen at (2-amu) and He at (4-amu) ... Oxygen will only stay mixed within the bottom most layer of the atmosphere. And likewise, water vapor (18-amu) will also be confined within this thin layer too.

I can visualize a so-called "Northern California Winter" happening - where one has a San Francisco type 'fog bank' blowing onto shore. You get a 'drizzle', stay wet all the time ... but no lightning, strong winds, hail. heavy rain ... for the H2/He part of the atmosphere is so light, one would form an unusual inversion layer. Water vapor would not be able to rise into it. Even methane wouldn't rise thru it.There's no other molecular substance that would vaporize, then cool off enough to condense, releasing heat of condensation either.

The result is that I am visualizing a desert world, sort of like Saudi Arabia around the Persian Gulf region ... Ocean and dry land - with fog, but no rain.

Now I'm really surprised by the great quantity of articles that have been written about this field within the last 25 years. Would you know of some good reference(s) to read?

 

[rootone]

What we can be pretty certain about is that anything similar to life as we think of it has to involve carbon chemistry.
Only Silicon has somewhat similar chemistry but it is nowhere close to as versatile as Carbon.

 

[mfb]

My comment was mainly about gas giants, I don’t know the wind patterns of Super Earths with a very dense atmosphere.
In the absence of any wind, oxygen on a Super Earth would still have a scale height of a few kilometers, while the hydrogen and helium partial pressure wouldn’t change much over that length. Wind would distribute the oxygen even better.