Here's a short story:

The abbreviation myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.6 teraseconds. 

Myr is in common use where the term is often written, such as in Earth science and cosmology. Myr is seen with "mya", "million years ago". Together they make a reference system, one to a quantity, the other to a particular place in a year numbering system that is "time before the present". 

Myr is deprecated in geology, but in astronomy "myr" is standard. Where "myr" "is" seen in geology it is usually "Myr" (a unit of mega-years). In astronomy it is usually "MYR" (million years). 

In geology the debate of the millennia concerns the use of "myr" remains open concerning "the use of "Myr" plus "Mya"" versus "using "Mya" only". In either case the term "Ma" is used in geology literature conforming to ISO 31-1 (now ISO 80000-3) and NIST 811 recommended practices. Traditional style geology literature is written The "ago" is implied, so that any such year number "X Ma" between 66 and 145 is "Cretaceous", for good reason. But the counter argument is that having "myr" for a duration and "Mya" for an age mixes unit systems, and tempts capitalization errors: "million" need not be capitalized, but "mega" must be; "ma" would technically imply a "milliyear" (a thousandth of a year, or 8 hours). On this side of the debate, one avoids "myr" and simply adds "ago" explicitly (or adds "BP"), as in In this case, "79 Ma" means only a quantity of 79 million years, without the meaning of "79 million years ago". (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: is myr roughly the same as mya in amount?
Guess: yes

Question: what does mya stand for?
Guess: million years ago

Question: and myr?
Guess: million years

Question: how many teraseconds does it represent?
Guess: 31.6

Question: do they use it in astronomy?
Guess: yes

Question: how about in geology?
Guess: no

Question: is there a debate between myr and mya usage?
Guess: yes

Now answer the following question in the same format.

Question: which one is favored?

the term "Ma"