131–140 of 180 posts
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One thing I do agree with you: answering that an invisible dude did everything we don't get is much simpler indeed. Calling that a truth though.
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The timing of the delivery is what's important here. These building blocks, organic matter, and water would have been depleted in the proto-Earth due to Solar irradiation. There needs to be some mechanism that delivers these ingredients from the outer Solar System. Bombardment by smaller rocks makes the most sense, and was likely triggered by the migration of Giant Planets, leading to a period of heavy bombardment (o…
Huh? Those smaller rocks would be even more irradiated, as they have no atmosphere? They’d also have to contend with re-entry.
The fragility of life-as-we-know-it that has undergone serial passage in an environment largely shielded from radiation, is not necessarily representative of putative life-forms carried by little rocks in space.
I am neither convinced for nor against the idea that life may have been carried over by interstellar rocks: on the one hand, its a major promiscuity between celestial bodies within star systems, galaxies, etc. on the other hand since we haven't discovered other life forms yet we have no idea on the missing probability densities of life in the bulk of the universe, so the Bayesian catapult can swing either way, we just lack the data for now.
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Life cannot appear in any of the small bodies that become meteors, because there is no source of energy for it. Life can appear only on big planets or on big satellites, like the big satellites of Jupiter and Saturn, if they have a hot interior and volcanism. Volcanism brings at the surface substances that are in chemical equilibrium at the high temperatures of the interior, but which are no longer at chemical equili…
> no source of energy Asteroids early in the solar system would be very radioactive due to short lived isotopes formed during the formation of the solar system. The existence of these isotopes is known from the patterns of decay products found in asteroids. The current guess is the early protoplanetary disk was bombarded by intense GeV-scale protons accelerated in the shock of a nearby supernova, causing large scale…
While a little radiation might have been beneficial at a later stage in the evolution of living beings, by increasing the frequency of random mutations, for a faster evolution, for the early living beings the only effect of radiation would have been to destroy them and prevent them for having descendants.
The only positive effect of the increased radioactivity in the early Solar System is that it is possible that not only the planets but also some smaller asteroids might have had warm interiors and volcanism.
So in none of the huge number of small bodies that exist in the Solar System there have ever been conditions for the appearance of life, but perhaps on some of the bigger asteroids there might have been such conditions, if they also had water and volatile chemical elements, besides a warm interior.
If life has ever appeared in such a place it must have used the same sources of energy that are known to have been used by the ancestors of life on Earth, i.e. gases and ionic gradients produced by chemical reactions between water and volcanic rocks.
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Life cannot appear in any of the small bodies that become meteors, because there is no source of energy for it. Life can appear only on big planets or on big satellites, like the big satellites of Jupiter and Saturn, if they have a hot interior and volcanism. Volcanism brings at the surface substances that are in chemical equilibrium at the high temperatures of the interior, but which are no longer at chemical equili…
> because there is no source of energy for it. Couldn't it have started in the accretion disk?
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We know 2 things that are apparently incoherent: 1 - Abiogenesis is incredibly rare. We don't know how much exactly, but it's a lot. 2 - Abiogenesis happened on Earth about as soon as it became possible. Where "as soon as" means within half a billion years, but it's still way quicker than its rarity implies. A lot of people think panspermia is what made those two happen. Life had about a full billion years to appear…
People make the inference that "early occurence of life" implies "life must be easy to start". But that inference requires the assumption that the chance of OoL (origin of life) remains mostly constant with time. An alternative would be that the conditions under which life could arise are transient, so life either starts early or not at all. We don't know enough about OoL to rule this out. Some chemicals that might b…
However, I would not describe those as small. The majority of the interplanetary bodies that orbit the Sun and which fall from time to time on Earth as meteorites are far too small to have ever had conditions for the appearance of life.
Even an asteroid like that which has wiped out the dinosaurs, with a diameter of a few km could not ever have suitable conditions.
Only relatively large asteroids, presumably with diameters from tens of km to hundreds of km, might have had warm interiors and volcanism for enough time to allow the appearance of life.
Such asteroids must also have been among those distant from the Sun, in order to contain enough water and volatile chemical elements.
The fact that the most volatile chemical elements are those most important for life is not due to chance, but due to the necessity. The volatile elements are those prone to forming covalent chemical bonds. Unlike the metallic or the ionic chemical bonds, the covalent bonds are strictly required for forming the complex molecular structures that may lead to living beings.
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Comets is where many astronomers have long thought the ocean came from. Comets are literal drops in our ocean. LOTS of comets. The atmosphere and the Earth at large would have been very different, and being bombarded by many giant space snowballs (along with asteroids) would have contributed materials. The missing part is, um, missing. We still do not know. However, these samples contained building blocks, not actual…
One thing that is beginning to be appreciated is, if you have building blocks, under the right conditions, you also have self replicating RNA. https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002...
The article is about a mechanism that may produce random nucleic acid molecules, i.e. molecules that do not replicate any template.
Reactions of this kind, producing random nucleic acids, must have existed long before the appearance of the first self-replicating RNA, thus before the appearance of any nucleic acid that could be inherited by the descendants of a living being and that could provide any useful feature for that living being.
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Wouldn't a big enough asteroid have an inner part which survives entry? You seem to be saying that it's impossible for any meteorite that might have these chemicals to not be completely vaporized which seems doubtful. Have you got a source?
So you survived re-entry. Now, you get to survive impact. Seems like the energy released would also be damaging
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>However, any RNA-based catalyst could have appeared only at a later time after the establishment of RNA self-replication. RNA by virtue of its biochemistry is capable of self replication already. Sequence affinity alone is sufficient to drive structure formation. But without a template, structure can also form on its own (example of an open access paper exploring one such mechanism under certain conditions, 1). This…
Nope. RNA is not capable of self replication. RNA by virtue of its biochemistry is only capable to be used as a template for replication, but the copying of the template must be done by a different molecular machinery. If you put almost any RNA molecule in a jar together with monomers, you can wait until the end of time to see its replication. Normally, RNA can be replicated only by a special enzyme, a RNA-dependent…
Anyone else think a universal intelligence is behind seeding planets with these rocks?
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read up on the RNA world theory, it's so cool
Parts of the RNA world theory are correct, but other parts are completely bogus and completely illogical. What is correct is that RNA must have existed a very long time before DNA, during which RNA was the only nucleic acid. Moreover, self-replicating RNA must have existed before ribosomes and proteins (where "protein" means a polypeptide that is synthesized using a RNA template). It should be obvious that neither ri…