Comment by BinaryAsteroid
6 days ago
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 (on a bare Earth -- no oceans, no volcanoes).. https://en.wikipedia.org/wiki/Nice_model
Huh? Those smaller rocks would be even more irradiated, as they have no atmosphere?
They’d also have to contend with re-entry.
It would’ve been specifically asteroids from beyond the "frost line", where it’s cold enough for volatile substances to coalesce and stay solid.
"volatile substances" is doing a lot of work. This means water and organics. Literal cold-storage seeds of life.
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The smaller rocks are composed of those materials in solid state (e.g., ice not water). They are less irradiated as they are further away from the Sun (think the asteroid belt and beyond). Atmospheric entry (if that's what you mean) is irrelevant. What matters here is the transport of materials from a place where they could have formed, to a place where they couldn't.
Atmospheric entry is completely relevant because some people have made the illogical claim that meteorites falling on Earth could have contributed with such complex organic substances, like the nucleobases, to the appearance of life on Earth.
The icy bodies from the outer Solar System that contain such organic substances are very easily vaporized during entry in the atmosphere of the Earth, so only a negligible fraction, if any, of the organic substances originally present in such a body would reach the surface of the Earth.
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> Atmospheric entry (if that's what you mean) is irrelevant.
I think the OP meant that Earths magnetic field and atmosphere shields any terrestrial matter far more than than a bare asteroid that has no such protections, so it seems implausible at first glance that these things would develop or survive in open space rather than here.
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The earths poles?
Those smaller rocks are in the outer solar system, where the solar irradiation is lower. But the way they are composed is lots of ices (volatile molecules in solid form) being built on the silicate/graphite refractory core. The ices remain preserved in the environment provided by the outer solar system.
Extra terrestrial propagation of life, if real would have evolved to have non-zero survival rates in interstellar radiation regimes and timescales.
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.
Meteorites are generally cold when they reach the surface of the earth. The heat of reentry is very brief and generally just on the surface. That's my understanding.
The surfaces are typically melted - the ones that don’t just explode anyway.
Icy meteorites never survive re-entry that I’m aware of; and most carbon/chondrite ones don’t either, but they are the most common type that do. They tend to be ‘dry’, however.
Re-entry is a very ‘angry’ process.
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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 simple truth" being Genesis, for which there can be no evidence possible?
pray tell, where do we learn this simple truth?
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