8 ms·

I always wondered why we are overly focused on the conditions that created life on earth. Arguably it makes sense to see similar conditions lead to life. But do

by toshk 6y ago

I always wondered why we are overly focused on the conditions that created life on earth. Arguably it makes sense to see similar conditions lead to life. But do we really know enough to assume that's only way?

freehunter 6y ago
Because it’s hard to detect life on other planets. It’s easier if we know what we’re looking for. We know where we came from, so it’s easier to detect.
renewiltord 6y ago
Well, look at it this way: you left your home in the morning for work, went to lunch, went back to work, met a friend for coffee, dropped by the office to pick up your stuff, then got home and found you didn't have your wallet. You know that, in the past when you lost your wallet, you dropped it somewhere or you left it behind somewhere. However, because you are a free individual and because the universe is full of possibilities (including the event that the quantum froth poofed your wallet away and created an identical one in your hedge), you can do practically anything now in search of your wallet. Do you: * Retrace your steps to see if your wallet is anywhere along the path * Call your mother and see if she has your wallet * Begin a global wallet-hunt in case the wallet was transported to Cuba Like most people you have an intuitive understanding of what to do: Given limited resources you should allocate them in order of decreasing likelihood of success. Most things do not lead to life. Our prior on "There is silicon-potassium self-replication on Charon" is pretty low because our prior on "X self-replication" is pretty low for most things. Try it out. Suggest an alternative and honestly set your priors on it, then condition those priors on the evidence that you have seen on Earth, and the limited evidence from the Moon and Mars. Now look at those posteriors for your alternative and compare it with the kind of life we know. Almost certainly microscopic, but if it isn't, you should publish.
BurningFrog 6y ago
Everyone agrees that (1) as far as we know, life can arise from a zillion different circumstances, and/but (2) the sane thing is to first look for it in environments similar to the only place we know has life.
WhompingWindows 6y ago
Our biochemistry is based on the most frequently occurring elements in the solar system. It's the most likely biochemistry to use carbon, silicates for instance are much less likely for a number of reasons.
deleted 6y ago
[deleted]
gameswithgo 6y ago
water and carbon a both uniquely suited to self assembling complex stuff, so its bot crazy to assume those are likely involved
- bjo590 6y ago
  In addition, we have a large sample of water & carbon based life. We would be able to pick up on more subtle clues if we saw another water & carbon based life-form than if we found a life-form based on other raw materials. Being able to pick up on subtle clues is incredibly important for the search for microorganisms within our solar system, or to have any search of life outside or solar system that doesn't involve looking for signs of intelligence (Scanning for patterns in radio waves, looking for dyson sphere construction, etc).
at_a_remove 6y ago
Numerous other ideas exist for alien life, but most of them have their shortcomings. It all boils down to chemical reactions and physics. Imagine a universe of only helium. No valence electrons would be readily available, so chances are you are not going to see helium molecules. Lithium, sure, as a metal. Continue examining various smaller (and more plentiful elements). Fluorine? Well, only one slot available, so you can make molecules with two atoms, but no chains. If you have two slots open, you can make a chain, but little else. Although try making a chain of oxygen -- even the three-link ozone is not particularly stable. Carbon can have four different bonds going at once, which is pretty crazy, and so you want something with three or four slots available. But then you say, well, silicon could have four. And it could ... but for the fact that it is so huge by comparison to carbon (that whole other "electron shell") that it rarely has analogues to organic (carbon-based) compounds. Also, it doesn't like to do much until you get it fairly hot. So you climb back up a row and it looks like carbon, nitrogen, boron ... those are going to do your heavy lifting when you need multiple bonds, with hydrogen, oxygen, and the halogens or alkali metals somewhere on the outside. Hence carbon chauvinism. Carbon is something like the fourth most common element in the universe after all. Then you start talking about solvents -- all of this stuff has to slosh around in something after all, your chemistry experiments take place in liquids -- and the field is a bit wider but dang, water has some crazy properties that make it quite a catch when it comes to solvents. You've got temperature ranges: down in the single digits of Kelvin you're not going to have much chemistry happening, and up in the thousands of Kelvins even iron boils and then again, no more structure. Once you start looking for these various "sweet spots" it all comes down to finding a place where you can have liquids (your solvent), solids (for structure), and gases (even if they are dissolved in liquids). Combine that with the more common elements (especially those that are friendly to complex chemistry) and you have something not entirely un-Earthlike. There's tons of Wikipedia articles on it, but ... the restrictions of chemistry are the bulk of the culprit, I'm afraid.
- throwaway2048 6y ago
  Another problem with silicon is that its basic oxide (Silicon Dioxide) is a solid that is non-reactive with virtually everything. If you assume water based life, there is almost certainly going to be oxides involved, such as how CO2 is involved with earth life. And I think water based life chemistry is an extremely good bet, because alternative liquids based off of light, common elements are either only liquid at very low temps, (ammonia, methane) extremely reactive ( Hydrogen fluoride, hydrogen sulfide), or both. Another consideration with silicon is that the earth contains vastly more silicon than it does carbon (in many ways life on earth is fairly carbon starved), yet life based on carbon arose, not silicon.
PaulHoule 6y ago
If your definition of habitable is "has liquid water" probably most of the habitable places in the universe are like Ceres, the moons of Saturn, even deep inside Pluto. Between the effects of pressure, geothermal energy, and gravitational tides you find liquid water in those places more than the inner solar system where water gets evaporated and blown away. (The trouble is that those places don't have sunlight and probably fewer energy sources overall.) It could be the answer to why we don't meet aliens: they couldn't care less about dry places like the Earth. You could travel the stars hopping comet to comet, but after spending 10,000 years like that you might be comfortable enough in your lifestyle that you wouldn't want to stop at a star. (All contingent on solving the energy problem, either you get lucky and find a lot of uranium or you invent D-D fusion.)
- ncmncm 6y ago
  Rocky planets are interesting only to extreme primitives. Once you leave the nest, Oort cloud objects are the most useful. That is where to look for visitors.
  - 082349872349872 6y ago
    "But Moooooom, I hate having a few seconds lag to all my friends." "If all your friends descended to the bottom of a gravity well, you would too? After all, we're not savages."
- Symmetry 6y ago
  My pet theory is that life is pretty common in the universe, it happened on Earth almost as soon as the oceans formed. But photosynthesis, mitochondria, and multi-celularity each took a lot longer and probably represent the biggest barriers to intelligent life. Plus, as you say, most liquid water is in the deep dark under ice sheets far from the nearest star which makes photosynthesis difficult.
  - gus_massa 6y ago
    You are not so far from the current models. Take a look at https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_h... (I think multicelularity of eucaryotes is easier in comparison with the other two steps, it has evolved like 20 times. But in the timeline, it took a long time...)
JohnBooty 6y ago
But do we really know enough to assume that's only way? I've never heard anybody in the sciences make that assumption. It's just that other biochemistries are speculative at best. Searching for this stuff is time- and resource-intensive, so naturally we look for the sort of life in which we have some expertise. And to be fair, we are not exclusively looking for Earth-like biological markers. Lots of people looking out for signs of Dyson spheres or other biology-agnostic possible signs of life.

by toshk 6y ago

freehunter 6y ago

Because it’s hard to detect life on other planets. It’s easier if we know what we’re looking for. We know where we came from, so it’s easier to detect.

renewiltord 6y ago

Well, look at it this way: you left your home in the morning for work, went to lunch, went back to work, met a friend for coffee, dropped by the office to pick up your stuff, then got home and found you didn't have your wallet. You know that, in the past when you lost your wallet, you dropped it somewhere or you left it behind somewhere. However, because you are a free individual and because the universe is full of possibilities (including the event that the quantum froth poofed your wallet away and created an identical one in your hedge), you can do practically anything now in search of your wallet. Do you: * Retrace your steps to see if your wallet is anywhere along the path * Call your mother and see if she has your wallet * Begin a global wallet-hunt in case the wallet was transported to Cuba Like most people you have an intuitive understanding of what to do: Given limited resources you should allocate them in order of decreasing likelihood of success. Most things do not lead to life. Our prior on "There is silicon-potassium self-replication on Charon" is pretty low because our prior on "X self-replication" is pretty low for most things. Try it out. Suggest an alternative and honestly set your priors on it, then condition those priors on the evidence that you have seen on Earth, and the limited evidence from the Moon and Mars. Now look at those posteriors for your alternative and compare it with the kind of life we know. Almost certainly microscopic, but if it isn't, you should publish.

BurningFrog 6y ago

Everyone agrees that (1) as far as we know, life can arise from a zillion different circumstances, and/but (2) the sane thing is to first look for it in environments similar to the only place we know has life.

WhompingWindows 6y ago

Our biochemistry is based on the most frequently occurring elements in the solar system. It's the most likely biochemistry to use carbon, silicates for instance are much less likely for a number of reasons.

deleted 6y ago

[deleted]

gameswithgo 6y ago

water and carbon a both uniquely suited to self assembling complex stuff, so its bot crazy to assume those are likely involved

bjo590 6y ago
In addition, we have a large sample of water & carbon based life. We would be able to pick up on more subtle clues if we saw another water & carbon based life-form than if we found a life-form based on other raw materials. Being able to pick up on subtle clues is incredibly important for the search for microorganisms within our solar system, or to have any search of life outside or solar system that doesn't involve looking for signs of intelligence (Scanning for patterns in radio waves, looking for dyson sphere construction, etc).

at_a_remove 6y ago

Numerous other ideas exist for alien life, but most of them have their shortcomings. It all boils down to chemical reactions and physics. Imagine a universe of only helium. No valence electrons would be readily available, so chances are you are not going to see helium molecules. Lithium, sure, as a metal. Continue examining various smaller (and more plentiful elements). Fluorine? Well, only one slot available, so you can make molecules with two atoms, but no chains. If you have two slots open, you can make a chain, but little else. Although try making a chain of oxygen -- even the three-link ozone is not particularly stable. Carbon can have four different bonds going at once, which is pretty crazy, and so you want something with three or four slots available. But then you say, well, silicon could have four. And it could ... but for the fact that it is so huge by comparison to carbon (that whole other "electron shell") that it rarely has analogues to organic (carbon-based) compounds. Also, it doesn't like to do much until you get it fairly hot. So you climb back up a row and it looks like carbon, nitrogen, boron ... those are going to do your heavy lifting when you need multiple bonds, with hydrogen, oxygen, and the halogens or alkali metals somewhere on the outside. Hence carbon chauvinism. Carbon is something like the fourth most common element in the universe after all. Then you start talking about solvents -- all of this stuff has to slosh around in something after all, your chemistry experiments take place in liquids -- and the field is a bit wider but dang, water has some crazy properties that make it quite a catch when it comes to solvents. You've got temperature ranges: down in the single digits of Kelvin you're not going to have much chemistry happening, and up in the thousands of Kelvins even iron boils and then again, no more structure. Once you start looking for these various "sweet spots" it all comes down to finding a place where you can have liquids (your solvent), solids (for structure), and gases (even if they are dissolved in liquids). Combine that with the more common elements (especially those that are friendly to complex chemistry) and you have something not entirely un-Earthlike. There's tons of Wikipedia articles on it, but ... the restrictions of chemistry are the bulk of the culprit, I'm afraid.

throwaway2048 6y ago
Another problem with silicon is that its basic oxide (Silicon Dioxide) is a solid that is non-reactive with virtually everything. If you assume water based life, there is almost certainly going to be oxides involved, such as how CO2 is involved with earth life. And I think water based life chemistry is an extremely good bet, because alternative liquids based off of light, common elements are either only liquid at very low temps, (ammonia, methane) extremely reactive ( Hydrogen fluoride, hydrogen sulfide), or both. Another consideration with silicon is that the earth contains vastly more silicon than it does carbon (in many ways life on earth is fairly carbon starved), yet life based on carbon arose, not silicon.

PaulHoule 6y ago

If your definition of habitable is "has liquid water" probably most of the habitable places in the universe are like Ceres, the moons of Saturn, even deep inside Pluto. Between the effects of pressure, geothermal energy, and gravitational tides you find liquid water in those places more than the inner solar system where water gets evaporated and blown away. (The trouble is that those places don't have sunlight and probably fewer energy sources overall.) It could be the answer to why we don't meet aliens: they couldn't care less about dry places like the Earth. You could travel the stars hopping comet to comet, but after spending 10,000 years like that you might be comfortable enough in your lifestyle that you wouldn't want to stop at a star. (All contingent on solving the energy problem, either you get lucky and find a lot of uranium or you invent D-D fusion.)

ncmncm 6y ago
Rocky planets are interesting only to extreme primitives. Once you leave the nest, Oort cloud objects are the most useful. That is where to look for visitors.
- 082349872349872 6y ago
  "But Moooooom, I hate having a few seconds lag to all my friends." "If all your friends descended to the bottom of a gravity well, you would too? After all, we're not savages."
Symmetry 6y ago
My pet theory is that life is pretty common in the universe, it happened on Earth almost as soon as the oceans formed. But photosynthesis, mitochondria, and multi-celularity each took a lot longer and probably represent the biggest barriers to intelligent life. Plus, as you say, most liquid water is in the deep dark under ice sheets far from the nearest star which makes photosynthesis difficult.
- gus_massa 6y ago
  You are not so far from the current models. Take a look at https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_h... (I think multicelularity of eucaryotes is easier in comparison with the other two steps, it has evolved like 20 times. But in the timeline, it took a long time...)

JohnBooty 6y ago

But do we really know enough to assume that's only way? I've never heard anybody in the sciences make that assumption. It's just that other biochemistries are speculative at best. Searching for this stuff is time- and resource-intensive, so naturally we look for the sort of life in which we have some expertise. And to be fair, we are not exclusively looking for Earth-like biological markers. Lots of people looking out for signs of Dyson spheres or other biology-agnostic possible signs of life.