Billion years
The billion year , sometimes also the giga year , is a unit of time used in geology and cosmology . It is with billion years or very rarely with billion years. abbreviated. In the specialist literature, based on the SI units , the abbreviation Ga (" Gigaannum ") can also be found.
Processes such as the formation of galaxies , phases of star development and the development of planets take place on a time scale of billions of years. The age of the universe according to the current state of science, according to the standard model of cosmology , is about 13.8 Ga, the age of the solar system about 4.6 Ga.
To be distinguished from the billion years, which denotes a period without a reference point, Gya is for English Giga-years ago (or Bya for billion years ago ), the designation for a point in time relative to the geological present in historical geology . For example, 4.6 Gya is the beginning of the Hadaic on earth - that is, 4.6 billion years before “today”. The duration of the Hadaicum is estimated at around 0.6 Ga.