Ma versus Myr
John Harper
between them? Ma seems to be more often used for a period finishing now
("The K-T boundary is at about 65 Ma") but either seems to be used for a
million years in general ("Plate angular velocities then and now are of
the order of 1 deg/Myr" or "The half-life of U235 is 704 Ma"). Is the
usage the same among geologists, geophysicists, and nuclear physicists?
John Harper Mathematics Dept. Victoria University Wellington New Zealand
carol raymond
Ma is properly used to express an age, whereas myr expresses
a length of time. Ma replaces "m.y.b.p" or million years before
present, in geology and geophysics. It would seem that the usage
you cite regarding the half-life of uranium is incorrect.
Carol
Erik Max Francis
> Ma and Myr both seem to mean a million years. Is there any clear difference
> between them?
I believe the term 'a' comes from "annum," which clearly means the
same thing as years. The only drawback from using this unit is that
it could be familiar with the (now possibly defunct) are, a unit of
area, from which the hectare is derived (even though hecto- is also
now a possibly defunct SI prefix).
I personally use y for years.
Erik Max Francis, &tSftDotIotE ...!uuwest!alcyone!max m...@alcyone.darkside.com
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koen...@abmx.rz.rwth-aachen.de
>Ma and Myr both seem to mean a million years. Is there any clear difference
>
>John Harper
Myr stands for Million years, Ma stands for Million anni, the latter
being the plural of Latin "annus", year. There is no difference in the
meaning.
Falk Koenemann
LARRIETL
In a former article we saw...
---begin former article---
From: koen...@abmx.rz.rwth-aachen.de
Subject: Re: Ma versus Myr
Date: 9 Feb 1994 13:06:36 GMT
In article <2j8th3$l...@st-james.comp.vuw.ac.nz>, har...@kauri.vuw.ac.nz (John
>Ma and Myr both seem to mean a million years. Is there any clear difference
>between them? Is the
>usage the same among geologists, geophysicists, and nuclear physicists?
>
>John Harper
Myr stands for Million years, Ma stands for Million anni, the latter
being the plural of Latin "annus", year. There is no difference in the
meaning.
Falk Koenemann
---end former article---
and LARR...@ctrvx1.Vanderbilt.Edu (LARRIETL) comments...
My understanding has always been that Ma refers to million years ago (before
the present) i.e. 100 Ma would be in the Cretaceous. On the other hand M.y.
refers to a duration or interval. i.e. the 100 m.y. history of deposition in
this basin.
Theo Larrieu
Xavier Llobet EPFL - CRPP 1015 Lausanne CH
:Ma and Myr both seem to mean a million years. Is there any clear difference
I'd rather use Ma, as Myr is too "English-centered"
-xavier
Bernhardt Sainieidukat
: From: koen...@abmx.rz.rwth-aachen.de
: In article <2j8th3$l...@st-james.comp.vuw.ac.nz>, har...@kauri.vuw.ac.nz (John
: >Ma and Myr both seem to mean a million years. Is there any clear difference
: >between them? Is the
: >usage the same among geologists, geophysicists, and nuclear physicists?
: Myr stands for Million years, Ma stands for Million anni, the latter
: being the plural of Latin "annus", year. There is no difference in the
I believe the M in Ma stands for Mega, as in Mega anni
and U.S. "billion" (10^9) years would be Ga = Giga anni.
Thomas M. Boyd
That may be correct, but accepted usage, i.e., usage as dictacted by
the copy editors at JGR indicate that Ma refers to millions before
present, and Myr stands for a length of time without reference to
present time, as Carol has previously posted.
Tom Boyd
Colorado School of Mines
tb...@milne.mines.colorado.edu