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 be needed for OoL, like ammonia, are not stable for long. And if life originated in small asteroids, this might have only a few million years for it to occur while they are still warm enough from early short lived radioisotopes like Al-26.

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adrian_b 6 hours ago | parent [-]

It is indeed possible that in the early Solar System, before the short-lived radioactive elements completely decayed, there were some asteroids with good conditions for the appearance of life.

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.

	▲	pfdietz 2 hours ago \| parent [-]
		> 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. So what? The meteorites that fall to Earth were not that size for their entire existence. They are fragments of larger bodies that have collided over the billions of years. Iron meteorites, for example, are remnants of the cores of larger bodies that were big enough to undergo melting and differentiation in the early solar system. Moreover, "not all places are suitable for OoL, therefore no places are suitable for OoL" would be a non sequitur, so I don't see how what you're trying to say there leads anywhere useful.