Origin of the Rocky Planet Water, Carbon and Nitrogen

The most basic requirement for life to start is a supply of the necessary chemicals, mainly water, reduced carbon and reduced nitrogen on a planet suitable for life. The word reduced means the elements are at least partly bound with hydrogen. Methane and ammonia are reduced, but so are hydrocarbons, and aminoacids are at least partly reduced. The standard theory of planetary formation has it (wrongly, in my opinion) that none of these are found on a rocky planet and have to come from either comets, or carbonaceous asteroids. So, why am I certain this is wrong? There are four requirements that must be met. The first is, the material delivered must be the same as the proposed source; the second is they must come in the same proportions, the third is the delivery method must leave the solar system as it is now, and the fourth is that other things that should have happened must have.

As it happens, oxygen, carbon, hydrogen and nitrogen are not the same through the solar system. Each exists in more than one isotope (different isotopes have different numbers of neutrons), and the mix of isotopes in an element varies in radial distance from the star. Thus comets from beyond Neptune have far too much deuterium compared with hydrogen. There are mechanisms by which you can enhance the D/H ratio, such as UV radiation breaking bonds involving hydrogen, and hydrogen escaping to space. The chemical bonds to deuterium tend to be several kJ/mol. stronger than bonds to hydrogen. The chemical bond strength is actually the same, but the lighter hydrogen has more zero point energy so it more easily breaks and gets lost to space. So while you can increase the deuterium to hydrogen ratio, there is no known way to decrease it by natural causes. The comets around Jupiter also have more deuterium than our water, so they cannot be the source. The chondrites have the same D/H ratio as our water, which has encouraged people to believe that is where our water came from, but the nitrogen in the chondrites has too much 15N, so it cannot be the source of our nitrogen. Further, the isotope ratios of certain heavy elements such as osmium do not match those on Earth. Interestingly, it has been argued that if the material was subducted and mixed in the mantle, it would be just possible. Given that the mantle mixes very poorly and the main sources of osmium now come from very ancient plutonic extrusions, I have doubts on that.

If we look at the proportions, if comets delivered the water or carbon, we should have five times more nitrogen, and twenty thousand times more argon. Comets from the Jupiter zone get around this excess by having no significant nitrogen or argon, and insufficient carbon. For chondrites, there should be four times as much carbon and nitrogen to account for the hydrogen and chlorine on Earth. If these volatiles did come from chondrites, Earth has to be struck by at least 10^23 kg of material (that is, ten followed by 23 zeros). Now, if we accept that these chondrites don’t have some steering system, based on area the Moon should have been struck by about 7×10^21 kg, which is approximately 9.5% of the Moon’s mass. The Moon does not subduct such material, and the moon rocks we have found have exactly the same isotope ratios as Earth. That mass of material is just not there. Further, the lunar anorthosite is magmatic in origin and hence primordial for the Moon, and would retain its original isotope ratios, which should give a set of isotopes that so not involve the late veneer, if it occurred at all.

The third problem is that we are asked to believe that there was a narrow zone in the asteroid belt that showered a deluge of asteroids onto the rocky planets, but for no good reason they did not accrete into anything there, and while this was going on, they did not disturb the asteroids that remain, nor did they disturb or collide with asteroids closer to the star, which now is most of them. The hypothesis requires a huge amount of asteroids formed in a narrow region for no good reason. Some argue the gravitational effect of Jupiter dislodged them, but the orbits of such asteroids ARE stable. Gravitational acceleration is independent of the body’s mass, and the remaining asteroids are quite untroubled. (The Equivalence Principle – all bodies fall at the same rate, other than when air resistance applies.)

Associated with this problem is there is a number of elements like tungsten that dissolve in liquid iron. The justification for this huge barrage of asteroids (called the late veneer) is that when Earth differentiated, the iron would have dissolved these elements and taken them to the core. However, they, and iron, are here, so it is argued something must have brought them later. But wait. For the isotope ratios this asteroid material has to be subducted; for them to be on the continents, they must not be subducted. We need to be self-consistent.

Finally, what should have happened? If all the volatiles came from these carbonaceous chondrites, the various planets should have the same ratio of volatiles, should they not? However, the water/carbon ratio of Earth appears to be more than 2 orders of magnitude greater than that originally on Venus, while the original water/carbon ratio of Mars is unclear, as neither are fully accounted for. The N/C ratio of Earth and Venus is 1% and 3.5% respectively. The N/C ratio of Mars is two orders of magnitude lower than 1-2%. Thus if the atmospheres came from carbonaceous chondrites:

Only the Earth is struck by large wet planetesimals,

Venus is struck by asteroidal bodies or chondrites that are rich in C and especially rich in N and are approximately 3 orders of magnitude drier than the large wet planetesimals,

Either Earth is struck by a low proportion of relatively dry asteroidal bodies or chondrites that are rich in C and especially rich in N and by the large wet planetesimals having moderate levels of C and essentially no N, or the very large wet planetesimals have moderate amounts of carbon and lower amounts of nitrogen as the dry asteroidal bodies or chondrites, and Earth is not struck by the bodies that struck Venus,

Mars is struck only infrequently by a third type of asteroidal body or chondrite that is relatively wet but is very nitrogen deficient, and this does not strike the other bodies in significant amounts,

The Moon is struck by nothing,

See why I find this hard to swallow? Of course, these elements had to come from somewhere, so where? That is for a later post. In the meantime, see why I think science has at times lost hold of its methodology? It is almost as if people are too afraid to go against the establishment.


6 thoughts on “Origin of the Rocky Planet Water, Carbon and Nitrogen

  1. Superb reasoning and very enlightening. I was a bit aware of the isotope problems with comets shooting down the water origin, but this goes much further. Notice it looks like many exoplanets are full of water. Seems clear the water comes with the planet formation…

    For whatever it’s worth, I suggested the Moon was created from Earth by nuclear explosions plus rotation… I admit the theory is farfetched, emotionally speaking, but the logic sounds plausible, at least to me….

    • Hello Patrice, Your link is imaginative at least. The Mars-sized collision theory, as you say, has a lot of problems and frankly I think it is just plain wrong, but there is an alternative involving collisions. Also, your argument about a highly elliptical orbit may not be correct. If it is elliptical, and close enough to generate significant tides, the tides circularize the orbit, at least to a high degree.

      In a later post I shall explain how I think the Earth formed, and why it has water, but first I have to consider the rest of the solar system because there are a number of trends that make my concept far more likely.

      • I didn’t use high ellipticity, I probably mis-express myself… One can combine my nuclear ejection theory with coplanar mini collision (so not on Mars size body). The whole thing would have looked like one of these spirals generated by some stars… If a star can do it, so could the nuclear boiling Earth…

  2. Patrice, my feeling is he Earth’s accretion was not that hot and I think the argument for a magma ocean is weak, but if there were enough hot nuclear isotopes, I guess it can’ be ruled out on evidence. It will take me a little while to get to this, though.

    • Well Earth melted, to start with. At least that’s what I learned as a child… 😉 The old theory was that Earth started very hot, then cooled. MY own variant was that Earth came equipped with a nuclear reactor. I suggested that to a young, prize adorned geophysicist at Berkeley, and he accused me stridently after a while, so much so he made himself look ridiculous in front of his wife who went on to marry someone else. That made him even angrier.

      15 years later, he tried to make amends, wrote me something sweet, but I never saw him again. Now official literature says I was right (I am of course never quoted).

      All this to say I believe in the magma ocean… But a local magma theory, from local nukes, and, or local impacts work just as well…

      • The issue is somewhat complicated by the presence of pressure. You may not realise this, but at the bottom of the mantle, xenon is a very high melting solid. I shall discuss this more properly in a later post – it is too complicated for a simple answer, and it is probably of sufficient interest for others. It is an interesting issue, though, and of course there was a lot of radioactive decay heat.

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