Most abundant active ingredients ≈ life’s
consider the cloud’s top ingredients: atoms of hydrogen, helium, oxygen, carbon, and nitrogen. Sound familiar? Except for helium, which is chemically inert, those elements are the main ingredients of life as we know it. Given the stunning variety of molecules those atoms can form, both with themselves and with others, they are also likely to be the ingredients of life as we don’t know it.
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Is life chemically special? The Copernican principle suggests that it probably isn’t. Aliens need not look like us to resemble us in more fundamental ways. Consider that the four most common elements in the universe are hydrogen, helium, carbon, and oxygen. Helium is inert. So the three most abundant, chemically active ingredients in the cosmos are also the top three ingredients in life on Earth. For this reason, you can bet that if life is found on another planet, it will be made of a similar mix of elements. Conversely, if life on Earth were composed primarily of, for example, molybdenum, bismuth, and plutonium, then we would have excellent reason to suspect that we were something special in the universe.
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Complex organic compounds abound in molecular clouds
- Demonstrate the ease of synthesis of prebiotic chemicals
Carbon monoxide (CO), for instance, stabilizes long before the carbon condenses into dust, and molecular hydrogen (H2) becomes the prime constituent of cooling gas clouds, now sensibly called molecular clouds. Among the triatomic molecules that form next are water (H2O), carbon dioxide (CO2), hydrogen cyanide (HCN), hydrogen sulfide (H2S), and sulfur dioxide (SO2). There’s also the highly reactive triatomic molecule H3+, which is eager to feed its third proton to hungry neighbors, instigating further chemical trysts.
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As the cloud continues to cool, dropping below 100 degrees Kelvin or so, bigger molecules arise, some of which may be lying around in your garage or kitchen: acetylene (C2H2), ammonia (NH3), formaldehyde (H2CO), methane (CH4). In still cooler clouds you can find the chief ingredients of other important concoctions: antifreeze (made from ethylene glycol), liquor (ethyl alcohol), perfume (benzene), and sugar (glycoaldehyde), as well as formic acid, whose structure is similar to that of amino acids, the building blocks of proteins.
The current inventory of molecules drifting between the stars is heading toward 130. The largest and most structurally intricate of them are anthracene (C14H10) and pyrene (C16H10)
Originating in more extreme environments
- Geo-thermal powered, surface life came later
- Just not as visible
- Hint at possible ubiquitousness of life (not visible to us)
Life, far from being rare and precious, may be as common as planets themselves.
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Water’s density inversion
- Protects marine life during ice ages
water’s most remarkable feature is that, while most things—water included—shrink and become denser as they cool, water expands when it cools below 4 degrees Celsius, becoming less and less dense.
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Without this density inversion below 4 degrees, whenever the outside air temperature fell below freezing, the upper surface of a bed of water would cool and sink to the bottom as warmer water rose from below. This forced convection would rapidly drop the water’s temperature to zero degrees as the surface begins to freeze. The denser, solid ice would sink to the bottom and force the entire bed of water to freeze solid from the bottom up. In such a world, there would be no ice fishing because all the fish would be dead—fresh frozen.
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Same atomic/molecular rules anywhere
- Life elsewhere might be more familiar than we dare imagine
- E.g. carbon
If somewhere there’s another celestial body that bears any resemblance to our own planet, it may have run similar experiments with its similar chemical ingredients, and those experiments would have been choreographed by the physical laws that hold sway throughout the universe. Consider carbon. Its capacity to bind in multiple ways, both to itself and to other elements, gives it a chemical exuberance unequalled in the periodic table. Carbon makes more kinds of molecules (how does 10 million grab you?) than all other elements combined. A common way for atoms to make molecules is to share one or more of their outermost electrons, creating a mutual grip analogous to the fist-shaped coupler between freight cars. Each carbon atom can bind with one, two, three, or four other atoms in this way, whereas a hydrogen atom binds with only one, oxygen with one or two, and nitrogen with three. By binding to itself, carbon can generate myriad combinations of long-chain, highly branched, or closed-ring molecules. Such complex organic molecules are ripe for doing things that small molecules can only dream about. They can, for example, perform one kind of task at one end and another kind at the other; they can coil and curl and intertwine with other molecules, creating no end of features and properties.
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E.g. silicon
One problem with silicon—apart from its being a tenth as abundant as carbon—is the strong bonds it creates. When you link silicon and oxygen, for instance, you don’t get the seeds of organic chemistry; you get rocks.
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