Chemically, there Chlorine and Flourine could take the place of oxygen in all sorts of reactions. So the chlorine breathing aliens of 50s science fiction are chemically possible. But the problem is that chlorine is much much less common in the universe than oxygen, due to quirks of how atoms are/were formed in stars. Oxygen makes up a very large fraction of the Earth’s crust, chlorine makes up a trace. So how does a planet enriched in chlorine form? Where does the chlorine come from? The biosphere of this planet couldn’t contain the main stock of chlorine, the crust of the planet would be chlorides instead of oxides.
We know planets and comets and nebulae in the universe are stuffed full of oxygen in all sorts of compounds. Common oxygen combined with extremely common hydrogen creates water. But the amount of chlorine in the universe is a tiny fraction of the amount of oxygen, and so it is extremely unlikely that there are any chlorine planets.
Right. I think the issue is that I was thinking in geologic scales. Water hydrolyzes protiens and many things, but in the end it starts out and ends up as water. Water is an energetic minimum. The statement that water doesn’t participate in the chemistry of life is incorrect. I should have thought that through more.
Another way of looking at this question: Everywhere on Earth that we can look, there is life as long as there is water. This includes rocks a mile deep in the Earth’s crust, and ice-covered lakes in Antarctica. It includes the interior of Chernobyl (where mold is even using hard radiation for photosynthesis of sorts), near-boiling volcanic water, and poisonous lakes of arsenic. Furthermore, the consensus seems to be that life arose on Earth virtually as soon as it as possible for it to do so.
The conditions we’re seeing for extremophiles on Earth are present and geologically stable elsewhere in the solar system, such as Europa’s depths. If you believe that life spontaneously arose on Earth in just a few hundred million years, then it’s not such a stretch to think it might have done so elsewhere in a few billion.
On our planet, plants have provided the oxygen needed for other forms of life. Could it be possible that, say, a kind of bacteria would seek out chlore and somehow release large amounts of chlorine in the athmosphere, allowing chlorine breathing creatures to exist?
Sure, there would have to be some concentration of chlorine by the biosphere. But the oxygen on our planet wasn’t created by plants, it was already present. Plants just spewed it into the atmosphere. But the oxygen was already present in vast quantities, only a miniscule fraction of the oxygen on our planet is in the atmosphere as O2. Most of the oxygen on Earth is in rocks, and most of the rest is in water.
It’s easy to imagine a biosphere that uses chlorine and all sorts of chlorinated organic molecules. But the reason this never happened on Earth is that chlorine is an extremely rare element on Earth compared to hydrogen, cargon, oxygen, and nitrogen. And this is because chlorine is extremely rare in the universe compared to those other elements, Earth isn’t unusual. And it’s very hard to see how a planet dramatically enriched in chlorine could form. A planet with twice as much chlorine, or even ten times as much chlorine wouldn’t support a chlorinated biosphere, it would just have more chloride ions in the oceans.
Oxygen makes up almost 50% of the Earth’s crust, by weight. Chlorine is only .01%. It’s true that other elements essential for Earth life are fairly rare in Earth’s crust, like carbon and nitrogen. But even though carbon is essential for life, remember that your body is mostly water. And water is mostly oxygen. So your body is mostly made up of oxygen, by weight.
IANAChemist, but I’m learning from this thread a lot. I quoted this because I understood it; but, like many laymen, I can also not know the most basic things:
What does solvent mean? I know the word, but I though**t it is kind of passive, like formaldehyde holding–admitedy via some chemical process deemed appropriate for the task–the real object of interest, the body part. Is it that, in this analogy, traces of formaldehyde can be examined to see if they ever have had contact with the part (formaldehyde being H2O), (body part being organic molecule)?
Question 2: The JPL guy I mentioned in OP just casually mentioned “non DNA” processes.
2a): Which I have no idea of what the are. He certainly seemed comfortable with the idea.
2b): and kind of begs the question, is “life” defined DNA-based, or any process that fights, however long and in vain, against entropy?
Question 2b) has been kicked around a lot, to say the least, and it’s OK by me if it gets posted as a new thread, or not all.
****Plus, I appreciate the third general point, made by Chronos, of anthropomorphising, so to speak, the physical universe.
The most penetrating and extensive discussions of this I haver come across, sometimes in insane humor, are written by the “science fiction” author Stanislaw Lem.
A solvent is able to dissolve a particular material. Most people are used to the idea of a solvent in terms of paint. If you paint with an oil-based paint and them put the brush in water, the paint doesn’t mix with the water. Mostly, it just sticks to the brush. Put that same brush in something like acetone, and the paint dissolves - it colors the acetone and stops clinging to the brushes. The opposite is true with latex paint - it dissolves in water and will not do anything in acetone. (Actually, I assume that’s true; I’ve never tried putting water-based paints in acetone.)
Solvents are important to chemical reactions. You can mix two powders together and get no chemical reaction at all. But dissolve them first in water, and you may get some impressive reactions when you mix them.
non-DNA processes is probably just shorthand for life that didn’t evolve on Earth. (Though some life on Earth only uses RNA, so it may not be perfectly correctly.)
DNA is certainly not necessary for life. A proper definition of life is difficult to come up with. (Just search wikipedia for a definition of life). Any definition of life would have to include the ability to replicate itself, but it’s not that simple: viruses can only replicate with the help of a host cell, and we’d hesitate to ascribe life to an assembly line of machines that are building other assembly line machines.
I read somewhere that the proportionate distribution of the various elements in your body, by mass I think, is effectively identical to that of the universe overall.
First of all, by weight I’m assuming you mean mass. And second of all, 90% of the visible mass of the universe is Hydrogen perhaps, but 84% of the universe’s mass is dark matter. What percent of the human body is dark matter!!??
I hate to nitpick this, because either you mean by mass, or it’s a simple mistake, but water is, of course, comprised of twice as much hydrogen than oxygen.
