Comments on: The Goldilocks Conjecture https://habitablezone.com/2016/08/25/the-goldilocks-conjecture/ Tue, 07 Apr 2026 19:18:10 -0700 hourly 1 http://wordpress.org/?v=3.3.1 By: ER https://habitablezone.com/2016/08/25/the-goldilocks-conjecture/#comment-37383 ER Sun, 28 Aug 2016 13:58:55 +0000 https://www.habitablezone.com/?p=59408#comment-37383 DNA is shared by every single life form on earth. Does this mean that only DNA can handle biological reproduction? Would organisms on other planet use other molecules in their genetic coding? No one knows the answer to this. We do know that amino acids, the chemical building blocks of DNA and proteins, seem to form spontaneously in space through inorganic processes, but whether this means all life in the universe is DNA-based we just don't know. DNA is composed entirely of carbon, hydrogen, oxygen, nitrogen and phosphorus. But what about the rest? As you point out, there are chemical constraints. Water is just about the universal solvent. It is not only very common in the cosmos, in its liquid form it supports more complex solution reactions than any other known compound, and it does this at temperatures which are conducive to complex chemistries and molecular formation. Carbon is also common in the universe, it forms long chains and rings and has multiple valences, allowing it to enter into many combinations with other elements. Life based on ammonia and silicon (the nearest chemical analogues to water and carbon) is theoretically possible, but no one has a clue how, or if, it would come about. Oxygen is also very common, and is so chemically active it is available as an effective energy source in a variety of chemical reactions. Although many primitive organisms are anaerobic and find free oxygen toxic, all living things incorporate oxygen in their biochemistry. I am convinced that if we find life out there, it will be in a liquid water environment, and will be carbon-based. If it is complex life requiring a compact source of quick energy, it will probably be an oxygen breather. Phosphorus plays an important role in energy management at the cellular level. I suspect DNA, or something very similar to it, will be involved in extraterrestrial life, although I'm not as certain about that. Other than that, I think we can expect plenty of surprises. DNA is shared by every single life form on earth. Does this mean that only DNA can handle biological reproduction? Would organisms on other planet use other molecules in their genetic coding? No one knows the answer to this. We do know that amino acids, the chemical building blocks of DNA and proteins, seem to form spontaneously in space through inorganic processes, but whether this means all life in the universe is DNA-based we just don’t know. DNA is composed entirely of carbon, hydrogen, oxygen, nitrogen and phosphorus.

But what about the rest? As you point out, there are chemical constraints. Water is just about the universal solvent. It is not only very common in the cosmos, in its liquid form it supports more complex solution reactions than any other known compound, and it does this at temperatures which are conducive to complex chemistries and molecular formation. Carbon is also common in the universe, it forms long chains and rings and has multiple valences, allowing it to enter into many combinations with other elements. Life based on ammonia and silicon (the nearest chemical analogues to water and carbon) is theoretically possible, but no one has a clue how, or if, it would come about.

Oxygen is also very common, and is so chemically active it is available as an effective energy source in a variety of chemical reactions. Although many primitive organisms are anaerobic and find free oxygen toxic, all living things incorporate oxygen in their biochemistry.

I am convinced that if we find life out there, it will be in a liquid water environment, and will be carbon-based. If it is complex life requiring a compact source of quick energy, it will probably be an oxygen breather. Phosphorus plays an important role in energy management at the cellular level. I suspect DNA, or something very similar to it, will be involved in extraterrestrial life, although I’m not as certain about that.

Other than that, I think we can expect plenty of surprises.

]]> By: bowser https://habitablezone.com/2016/08/25/the-goldilocks-conjecture/#comment-37370 bowser Sat, 27 Aug 2016 18:53:13 +0000 https://www.habitablezone.com/?p=59408#comment-37370 We posit the habitable zone based upon how DNA responds to conditions on Earth. We don't know how it would adapt to millions of years of exposure to a different environment. Of course there are chemical constraints, what it can and can't adapt to chemically and it would need liquid water. Beyond that, though, DNA may have adapted to red dwarfs. After all, Barnum and Bailey hired them. We posit the habitable zone based upon how DNA responds to conditions on Earth. We don’t know how it would adapt to millions of years of exposure to a different environment. Of course there are chemical constraints, what it can and can’t adapt to chemically and it would need liquid water.
Beyond that, though, DNA may have adapted to red dwarfs. After all, Barnum and Bailey hired them.

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