Gya
Encyclopedia
In astronomy
, geology
, and paleontology
, Gya or Ga (for giga
years ago and gigaannum, respectively) is a year multiplied by one of the SI prefix multipliers. It is often used as a unit
of time
to denote length of time before the present. Specifically, one Gya ago is equal to 109 years ago.
A unit identical to Gya is bya
(for "billion
years ago"), which may be in more widespread use. However, some scientists prefer Gya because it uses the SI
prefix giga- and thus avoids confusion over whether the short-scale (American
) billion (109) or long-scale (former British
) billion (1012) is meant, as well as avoiding preference for one of the two definitions of billion over the other.
In some scientific literature, the term Gya has been replaced by Ga (Giga-annum).
Gya can also refer to a new unit of radiation exposure called the gray
. A 100 röntgen
dose of radiation is equivalent to 1 Gya, the gray dose in air.
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, geology
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, and paleontology
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
, Gya or Ga (for giga
Giga
Giga is a unit prefix in the metric system denoting a factor of billion . It has the symbol G.Giga is derived from the Greek γίγας, meaning 'giant'...
years ago and gigaannum, respectively) is a year multiplied by one of the SI prefix multipliers. It is often used as a unit
Units of measurement
A unit of measurement is a definite magnitude of a physical quantity, defined and adopted by convention and/or by law, that is used as a standard for measurement of the same physical quantity. Any other value of the physical quantity can be expressed as a simple multiple of the unit of...
of time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....
to denote length of time before the present. Specifically, one Gya ago is equal to 109 years ago.
A unit identical to Gya is bya
Bya
In astronomy, geology, and paleontology, bya or "b.y.a." is an acronym for billion years ago. This abbreviation is commonly used as a unit of time to denote length of time before the present...
(for "billion
1000000000 (number)
1,000,000,000 is the natural number following 999,999,999 and preceding 1,000,000,001.In scientific notation, it is written as 109....
years ago"), which may be in more widespread use. However, some scientists prefer Gya because it uses the SI
Si
Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...
prefix giga- and thus avoids confusion over whether the short-scale (American
American English
American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....
) billion (109) or long-scale (former British
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...
) billion (1012) is meant, as well as avoiding preference for one of the two definitions of billion over the other.
In some scientific literature, the term Gya has been replaced by Ga (Giga-annum).
Gya can also refer to a new unit of radiation exposure called the gray
Gray (unit)
The gray is the SI unit of absorbed radiation dose of ionizing radiation , and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter ....
. A 100 röntgen
Röntgen
The roentgen is a unit of measurement for exposure to ionizing radiation , and is named after the German physicist Wilhelm Röntgen...
dose of radiation is equivalent to 1 Gya, the gray dose in air.