Even carbon-based life forms on other planets are almost certainly going to be much different looking than what is/was here on Earth. Having a roughly similar sized worlds with somewhat similar major elements and roughly the sane gravity on it is in no way enough to ensure also similar life popping up.
Our planet has seen at least five mass extinction events that we currently know of. All of them due to potential different causes. (Six even, if we count the human race as a big enough cataclysm for life here on Earth). It is not far fetched to assume that other planets may not have seen the same events as Earth did. Or if they did, with a completely different outcome.
Heck, it took about three mass extinction events until trilobites bit the bullet for good. Chances are there may be water worlds out there in which their "pseudo-Paleozoic era" never came to an end. I'd giggle like a grade schooler if we'd ever see something like the Great Race of Yith.
Even carbon-based life forms on other planets are almost certainly going to be much different looking than what is/was here on Earth. Having a roughly similar sized worlds with somewhat similar major elements and roughly the sane gravity on it is in no way enough to ensure also similar life popping up.
Our planet has seen at least five mass extinction events that we currently know of. All of them due to potential different causes. (Six even, if we count the human race as a big enough cataclysm for life here on Earth). It is not far fetched to assume that other planets may not have seen the same events as Earth did. Or if they did, with a completely different outcome.
Heck, it took about three mass extinction events until trilobites bit the bullet for good. Chances are there may be water worlds out there in which their "pseudo-Paleozoic era" never came to an end. I'd giggle like a grade schooler if we'd ever see something like the Great Race of Yith.
I said similar shapes. There's only so many ways to move through a medium like water or across land that are efficient. That doesn't mean they won't look completely weird, though. We also have a lot of different looking things here on Earth and in it's past.
Superficially we do have animals that look kind of trilobite-like around today. The horse shoe crab
Sure, they're not exactly the same, trilobites are more elongated and have segmented shells, whereas the horse shoe crab has a single piece for it's top shell, but the general structure shares a lot of similarities.
The idea of convergent evolution is behind a lot of my reasoning we'd see familiar shapes on alien worlds. Bats and birds share a lot of traits, despite being completely different animals and dolphins and Ichthyosaurs share a lot in common.
This is an interesting documentary from National Geographic discussing possible ways alien life could evolve extrapolating from our current knowledge. If you can, watch the full documentary on National Geographic.
@mlnevese Don't worry, it is now. With the exception of that one fish gun which kinda metamorphoses into a octopus... tank... thing. GOSH WHAT WERE THEY THINKING?!
For those who might not be aware: the "silicon-based life" idea doesn't actually refer to computer-based life. The reason silicon has drawn some interest as a theoretical basis for life is because, like carbon, silicon is capable of forming four bonds per silicon atom, which means it could create the same double-sided strands that allow carbon to form highly complex molecules. Most elements can only create molecules of a certain level of complexity, but life requires much more complicated chemicals to self-replicate successfully. A protein molecule can involve hundreds of atoms bonded together, and you can really only get molecules that large when you can connect things in strands.
Thing is, we don't know if silicon could realistically form those complex strands and eventually result in self-replicating life, simply because we have no idea what the properties of those strands would be. You wouldn't be able to just take a typical hydrocarbon, replace all the carbon atoms with silicon, and expect it to work in any particular way. If silicon-based life did exist, it would probably be very radically different from carbon-based life. I recall that one of the theories said that silicon-based life would actually have to reside in sulfuric acid because water would not be a proper solvent for the right materials.
Carbon is much better than silicon (or germanium, etc..) for the backbone of organic chemistry. Although both have 4 unpaired electrons in the outer orbital, carbon's unpaired electrons are in the second orbital, which has a maximum of 8 electrons. So, bonding with 4 other atoms makes carbon's outer orbital full and very stable. In contrast, silicon's outer orbital is the third orbital, which can have a maximum of 18 electrons. So, a silicon atom with 4 bonds does not have a full complement of electrons in the outer orbital (8 of 18), and the bonds are therefore weaker than carbon bonds (about half as strong).
Further, carbon-carbon bonds are much stronger than silicon-silicon bonds, especially when immersed in a liquid. Chain molecules are essential for organic chemistry, but chains made with silicon rather than carbon easily break apart in solvents like water. Silicon also does not like to make double and triple bonds, which make some carbon molecules especially strong.
Another factor in carbon's favor is the abundance of oxygen in the universe. Oxygen is the third-most abundant element in the universe (after hydrogen and helium) and an excellent oxidizer (in the sense of causing another element to lose electrons) for organic reactions. However, while carbon and oxygen make CO2, a gas that can easily react with other molecules, silicon and oxygen make SiO2, i.e., quartz, a solid.
Silicon is over 100x more abundant than carbon on Earth. It is not a fluke that life is based on carbon chemistry rather than silicon. Carbon is just better suited for organic chemistry.
For those who might not be aware: the "silicon-based life" idea doesn't actually refer to computer-based life. The reason silicon has drawn some interest as a theoretical basis for life is because, like carbon, silicon is capable of forming four bonds per silicon atom, which means it could create the same double-sided strands that allow carbon to form highly complex molecules. Most elements can only create molecules of a certain level of complexity, but life requires much more complicated chemicals to self-replicate successfully. A protein molecule can involve hundreds of atoms bonded together, and you can really only get molecules that large when you can connect things in strands.
Thing is, we don't know if silicon could realistically form those complex strands and eventually result in self-replicating life, simply because we have no idea what the properties of those strands would be. You wouldn't be able to just take a typical hydrocarbon, replace all the carbon atoms with silicon, and expect it to work in any particular way. If silicon-based life did exist, it would probably be very radically different from carbon-based life. I recall that one of the theories said that silicon-based life would actually have to reside in sulfuric acid because water would not be a proper solvent for the right materials.
Carbon is much better than silicon (or germanium, etc..) for the backbone of organic chemistry. Although both have 4 unpaired electrons in the outer orbital, carbon's unpaired electrons are in the second orbital, which has a maximum of 8 electrons. So, bonding with 4 other atoms makes carbon's outer orbital full and very stable. In contrast, silicon's outer orbital is the third orbital, which can have a maximum of 18 electrons. So, a silicon atom with 4 bonds does not have a full complement of electrons in the outer orbital (8 of 18), and the bonds are therefore weaker than carbon bonds (about half as strong).
Further, carbon-carbon bonds are much stronger than silicon-silicon bonds, especially when immersed in a liquid. Chain molecules are essential for organic chemistry, but chains made with silicon rather than carbon easily break apart in solvents like water. Silicon also does not like to make double and triple bonds, which make some carbon molecules especially strong.
Another factor in carbon's favor is the abundance of oxygen in the universe. Oxygen is the third-most abundant element in the universe (after hydrogen and helium) and an excellent oxidizer (in the sense of causing another element to lose electrons) for organic reactions. However, while carbon and oxygen make CO2, a gas that can easily react with other molecules, silicon and oxygen make SiO2, i.e., quartz, a solid.
Silicon is over 100x more abundant than carbon on Earth. It is not a fluke that life is based on carbon chemistry rather than silicon. Carbon is just better suited for organic chemistry.
I agree 100% with what you said.
It would be pretty inefficient to breath oxygen and crap out silicon dioxide or monoxide. I suppose you could imagine some sort of creature that filters sand and derives energy from splitting oxygen from silicon, like how plants split oxygen from carbon for energy, but that seems really inefficient, too. Heh, maybe that's what the worms in Dune were doing. I couldn't see anything that uses that process for energy being able to move quickly or much at all.
Comments
Our planet has seen at least five mass extinction events that we currently know of. All of them due to potential different causes. (Six even, if we count the human race as a big enough cataclysm for life here on Earth). It is not far fetched to assume that other planets may not have seen the same events as Earth did. Or if they did, with a completely different outcome.
Heck, it took about three mass extinction events until trilobites bit the bullet for good. Chances are there may be water worlds out there in which their "pseudo-Paleozoic era" never came to an end. I'd giggle like a grade schooler if we'd ever see something like the Great Race of Yith.
Apropos trilobites:
I said similar shapes. There's only so many ways to move through a medium like water or across land that are efficient. That doesn't mean they won't look completely weird, though. We also have a lot of different looking things here on Earth and in it's past.
Superficially we do have animals that look kind of trilobite-like around today. The horse shoe crab
The idea of convergent evolution is behind a lot of my reasoning we'd see familiar shapes on alien worlds. Bats and birds share a lot of traits, despite being completely different animals and dolphins and Ichthyosaurs share a lot in common.
This is an interesting documentary from National Geographic discussing possible ways alien life could evolve extrapolating from our current knowledge. If you can, watch the full documentary on National Geographic.
Absolutely not off-topic.
Carbon is much better than silicon (or germanium, etc..) for the backbone of organic chemistry. Although both have 4 unpaired electrons in the outer orbital, carbon's unpaired electrons are in the second orbital, which has a maximum of 8 electrons. So, bonding with 4 other atoms makes carbon's outer orbital full and very stable. In contrast, silicon's outer orbital is the third orbital, which can have a maximum of 18 electrons. So, a silicon atom with 4 bonds does not have a full complement of electrons in the outer orbital (8 of 18), and the bonds are therefore weaker than carbon bonds (about half as strong).
Further, carbon-carbon bonds are much stronger than silicon-silicon bonds, especially when immersed in a liquid. Chain molecules are essential for organic chemistry, but chains made with silicon rather than carbon easily break apart in solvents like water. Silicon also does not like to make double and triple bonds, which make some carbon molecules especially strong.
Another factor in carbon's favor is the abundance of oxygen in the universe. Oxygen is the third-most abundant element in the universe (after hydrogen and helium) and an excellent oxidizer (in the sense of causing another element to lose electrons) for organic reactions. However, while carbon and oxygen make CO2, a gas that can easily react with other molecules, silicon and oxygen make SiO2, i.e., quartz, a solid.
Silicon is over 100x more abundant than carbon on Earth. It is not a fluke that life is based on carbon chemistry rather than silicon. Carbon is just better suited for organic chemistry.
I agree 100% with what you said.
It would be pretty inefficient to breath oxygen and crap out silicon dioxide or monoxide. I suppose you could imagine some sort of creature that filters sand and derives energy from splitting oxygen from silicon, like how plants split oxygen from carbon for energy, but that seems really inefficient, too. Heh, maybe that's what the worms in Dune were doing. I couldn't see anything that uses that process for energy being able to move quickly or much at all.