bya or b.y.a. is an
abbreviation
An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters or words taken from the full version of the word or phrase; for example, the word ''abbrevia ...
for "
billion
Billion is a word for a large number, and it has two distinct definitions:
*1,000,000,000, i.e. one thousand million, or (ten to the ninth power), as defined on the short scale. This is its only current meaning in English.
* 1,000,000,000,000, i.e ...
years ago". It is commonly used as a
unit of time
A unit of time is any particular time interval, used as a standard way of measuring or expressing duration. The base unit of time in the International System of Units (SI) and by extension most of the Western world, is the second, defined as a ...
to denote length of time before the present in 10
9 years. This
initialism
An acronym is a word or name formed from the initial components of a longer name or phrase. Acronyms are usually formed from the initial letters of words, as in ''NATO'' (''North Atlantic Treaty Organization''), but sometimes use syllables, as ...
is often used in the sciences of
astronomy
Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
,
geology
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...
, and
paleontology
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
.
The "billion" in bya is the 10
9 "billion" of the
short scale
The long and short scales are two of several naming systems for integer power of 10, powers of ten which use some of the same terms for different magnitudes.
For whole numbers smaller than 1,000,000,000 (109), such as one thousand or one m ...
of the
U.S.
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
,
[Gale, Joseph (2009). ''Astrobiology of Earth: The Emergence''. Oxford: Oxford University Press, p]
21.
/ref> not the long-scale 1012 "billion" of some Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
an usage. Billion by this convention (109) is often called a "thousand million" in the UK and a "milliard" in some other countries.[Chartrand, Mark (2004). ''Satellite Communications for the Nonspecialist''. New York: SPIE Press, p]
73.
/ref> For this reason, there is potential for some confusion, and some scientists prefer the unit Gya
A billion years or giga-annum (109 years) is a unit of time on the petasecond scale, more precisely equal to seconds (or simply 1,000,000,000 years).
It is sometimes abbreviated Gy, Ga ("giga-annum"), Byr and variants. The abbreviations Gya or ...
, while others prefer Ga (Giga-annum), however bya remains in more widespread use. In 1974, the UK switched from the long scale to the short scale.
Related units are mya ("million years ago), and byr ("billion years"). These are traditionally written in lowercase
Letter case is the distinction between the Letter (alphabet), letters that are in larger uppercase or capitals (or more formally ''majuscule'') and smaller lowercase (or more formally ''minuscule'') in the written representation of certain lang ...
. Ga or Gya has a capitalized first letter instead.
See also
* Chronology
Chronology (from Latin ''chronologia'', from Ancient Greek , ''chrónos'', "time"; and , '' -logia'') is the science of arranging events in their order of occurrence in time. Consider, for example, the use of a timeline or sequence of events. I ...
* Myr
* Before Present
Before Present (BP) years, or "years before present", is a time scale used mainly in archaeology, geology and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Becaus ...
References
Units of time
Chronology
Metrology
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