Megaanum, kiloannum, annum

[Lucus Eques]

Salvete omnes!

In geology I frequently deal with SI units and am often presented with terms like Ma : "megaanum" = one million years, or ka : "kiloannum" = one thousand years, et cetera. Wikipedia defines the SI unit annum as being the accusative singular of Latin annus, which of course you all know.

We will leave the repugnance of the formation of this term and its chimaeric Hellenized hybrids for another discussion.

My question relates to the usage of Ma, Ga, etc. I was told quite clearly by my professor in Geohistory that a number like 145 Ma denotes "145 million years ago," and that it is inappropriate to say that the dinosaurs lived for more than "100 Ma," and instead only correct to write "100 m. yr. [million years]." The SI units Ga, Ma, ka, and others always mean ago. I didn't like this limitation when I first heard it.

Given the accusative implication in the unit annum, can we justify this stance with grammar? To me, Latinly, the accusative usage of time would seem to indicate the very opposite, no?

I'd love it if Latin proved my professor and practice right, instead of quite wrong. That would make my life easier.

Quid censatis vosmet ipsi?

[Kasper]

Lucus, as a law student i feel you pain. Law remains packed full of latin maxims that are not understood by the professors that teach them.

It is inexplicable why textbooks translate maxims like "in pari delictu potior est positio defendentis", as "at equal fault each party is liable for its own damage".

Or why "opinio juris sive necessitatis" is considered to mean that the opinion held must be that the relevant rule 'must necessarily be law'.

And let's not speak of the nails-over-blackboard pronounciation of the most basic phrases such as 'prima facie'.

More to the point, of course the accusative indicates duration of time, you know these things much better than i do.

[Lucus Eques]

Wow, law sucks. At least I can enjoy Boston Legal, heh. Actually, I've never heard prima facie pronounced any other way than in my head, and it's nice there ... (gives a J.D.-like stare off into the distance like in Scrubs).

[adrianus]

I don't think "years ago" is an SI definition, Lucus. Ma = Mega ans/anni/years and Ga = Giga ans/anni/years in scientific writing with SI units. (You can use "y" and "yr" unofficially but "a" is proper for "an" (Fr.) or "annus", not "ago". The word "ago" may be understood in common practice but the "a" in the abbreviation means "ans" or "anni"). You may not be suggesting that the "a" refers to "ago", in any case.

Ut opinor, Luce, "Ma" abbreviatio "Million years ago" dicere non vult at magis "mega ans" vel "mega anni". De systemâ internationale, abbreviatio pro "annus" latinè vel "an" gallicè "a" probè est et hinc Ma = mega-anni et Ga = giga-anni.

Other than the Wiki article you refer to, I don't see anywhere the unit referred to as accusative only "annum". I think the Wiki article is wonky on this, if it suggests "annum" is the recognised unit. I think the author is shy about using "anni" because it sounds pedantic! Different countries spell the SI units after their fashions and "a" isn't 100% enshrined as a full SI unit for "year" (but it has almost got there). So I wouldn't worry about "the accusative implication in the unit annum". I think the author of the article is just a bit loose there. OED says it means both "years" and "years ago":

Ma n. [< M n. + a, SI symbol for ‘year’ (symbolic abbreviation for classical Latin annus year: see ANNALS n.)] Geol. and Palaeontol. million years, esp. million years before the present.

But I think your prof is right that "the dinosaurs lived for more than 100 Ma," is more ambiguous than "100 m. yr. [million years].", given the practice in the discipline, where you can say "the dinosaurs died out 65Ma".

[Lucus Eques]

I don't think "years ago" is an SI definition, Lucus. Ma = Mega ans/anni/years and Ga = Giga ans/anni/years in scientific writing with SI units. (You can use "y" and "yr" unofficially but "a" is proper for "an" (Fr.) or "annus", not "ago". The word "ago" may be understood in common practice but the "a" in the abbreviation means "ans" or "anni"). You may not be suggesting that the "a" refers to "ago", in any case.

Indeed, heh, I was not suggesting that, but thanks all the same.

Other than the Wiki article you refer to, I don't see anywhere the unit referred to as accusative only "annum". I think the Wiki article is wonky on this, if it suggests "annum" is the recognised unit. I think the author is shy about using "anni" because it sounds pedantic! Different countries spell the SI units after their fashions and "a" isn't 100% enshrined as a full SI unit for "year" (but it has almost got there). So I wouldn't worry about "the accusative implication in the unit annum". I think the author of the article is just a bit loose there. OED says it means both "years" and "years ago":

Ma n. [< M n. + a, SI symbol for ‘year’ (symbolic abbreviation for classical Latin annus year: see ANNALS n.)] Geol. and Palaeontol. million years, esp. million years before the present.

But I think your prof is right that "the dinosaurs lived for more than 100 Ma," is more ambiguous than "100 m. yr. [million years].", given the practice in the discipline, where you can say "the dinosaurs died out 65Ma".

Neat. Well, it's definitely "annum," per the practice and the pronunciation, which is why it confounded me for so long — if we take it as a neutered version of "annus," then perhaps the coined term "annum" can mean "year before present," so then we have "10 mega anna," ten million years ago.

[adrianus]

I think that, just as the "ago" is implied in English, you can imagine "ante" or "abhinc" + acc. in the Latin as implied for "Giga-annos". You wouldn't say "2Giga-annum" in Latin or in English, would you? Surely you would say, 2 Gigayears (ago), in English.

[Lucus Eques]

You would and do say "giga-annum" — "giga-years" is never said — 1Ga is pronounced either fully English ("one billion years") or fully "classical" ("one giga-annum"), while 1 b. yr. is only pronounced "one billion years."

[adrianus]

When I said you wouldn't say "giga-annum" (or "giga annum") in English or Latin, I was speaking too casually. In fact, both "giga annum" and "giga years" are commonly used in scientific writing in English today. (Just one recent example of the use of "giga years" is Takashi Okamoto, Rodrigo S. Nemmen and Richard G. Bower, "The impact of radio feedback from active galactic nuclei in cosmological simulations: formation of disc galaxies" Mon. Not. Royal Astronomical Society, January 2008, p.15). I was just recommending "giga years" to you as a way past your annoyance about "giga annum". "Billion years" may be nicer still, but there's a tiny chance of being misunderstood if you use the word billion internationally (10 to the power of 9 versus 10 to the power of 12), although mostly now people and official bodies go with 10 to the power of 9 for a billion.

I think your annoyance with the term "giga-annum" is very understandable. Here you have a noun "annum" introduced from Latin which is being used as a count noun, but which travels with a grammatical invisible elephant. If you don't have Latin, you are inclined to fudge the spoken word in the plural, avoiding "3.62 giga annums" [although if you can say "forums" and "memorandums" alongside "fora" and "memoranda", I suppose you can say "annums" but then you get angst-ridden worrying should be "annuses" or "anni" or "annos" even "anna"!], and settling for "3.62 giga annum". It has become an indeclinable count noun in this usage (although still not a mass noun or a collective noun). That's OK but it savours of archaic English, as with "He spent three year in the army", where the word hovers in a shady zone between "a three-year" and "a three-year period" --quasi noun, quasi adjective. The bottom line is it's in spoken and written use ("3.62 giga annum") and understandable, and that's one of the ways language evolves --the rules will be bent to accommodate dominant usage, eventually. That's why I like the plain English approach which says "Ga" = written abbrev. for "Giga annum" or "Giga an" (the ambiguity is an advantage here because it releases you from any felt Latin obligation) but prefers spoken English "giga years", which is also in use (believe me, it is) and understandable.