who only by moving can balance

Geochemistry is a compilation of imprecise, irreproducible and uncoordinated analyses.
(i) Keep the rocks in mind, for they cannot be reduced to analytical measurements; (ii) (from O. F. Tuttle) minerals are the archives of the rocks; (iii) keep filing [your] fingernails while waving [your] arms.

Relatedly: a lecturer's assertion during my undergrad that fundamentally you cannot argue with the rocks [ergo any theory you develop must be supported by the rocks], hence in part this poem of mine; and the general feeling among my group's principle investigators that geochemistry is fundamentally characterised by paranoia, and how relaxed you're willing to be about cleanliness.

Conference conference conference! Start of session two. As always, please feel encouraged to ask whatever questions you have, and I will do my best to answer them. It is also worth noting that there is an annual Lunar & Planetary Sciences conference, and that this meeting at the Royal Society took place in that context - and seems by all accounts to have been incredibly valuable!

After Kona [first big conference on Moon stuff] predominant view was that Moon was predominantly projectile. Now we believe that the Moon is largely Earth-like. [Let's add another clarifying note, actually: the Giant Impact Hypothesis is generally accepted, and assumes that something Really Big (Mars-sized) hit the Earth at some point - though as you've seen/will see from some of the other notes, exactly when is a matter of serious debate... anyway, so you've got this Huge Lump o' Rock hurtling in, and it smashes into the Earth, and largely vapourises both itself *and* some of the Earth, forming a mixture of the two. The question is: in that vapour, are the majority of the atoms from Earth or are the majority of the atoms from this Big Lump o' Rock From Outer Space? Increasingly, the geochemistry has us convinced that they have to be mostly from Earth - or that the projectile, via some mechanism, had a nearly identical isotope chemistry to the Earth. The latter is currently considered highly unlikely (or, er, grasping at straws), because what we know of Mars (one of the other rocky/terrestrial planets) is that its composition is MARKEDLY different to Earth's, whereas the Moon and the Earth are in most cases as close-as-damn-it identical. This is some of why everyone is so keen to get data from Mercury and Venus - it will let us know whether Mars is an anomaly among the terrestrial planets (i.e. Mercury/Venus/Earth all have similar compositions) or whether it's indicative of the general state of play (i.e. M/V/E all have different compositions). If the former, a projectile with a composition that matches the Earth's exactly is suddenly much more plausible - but the data we've got so far says Erm, Nope. Of course, instruments continue to improve... and there's a third option, which is very attractive, that the impact managed to effectively homogenise the projectile's matter with the proto-Earth's matter. This would neatly solve the problem of identical compositions, but we have no models at all that come anywhere close to being able to account for this.]

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