Annum

Annum is a Latin term meaning Year.

• Per annum means "occurring every year".

• Mega-annum, usually abbreviated as Ma, is a unit of time equal to one million (10⁶) years. It is commonly used in scientific disciplines such as Geology and Paleontology to signify very long time periods in the past. For example, the Dinosaur species Tyrannosaurus rex emerged approximately 65 Ma (65 million years) ago.

• Giga-annum, usually abbreviated as Ga, is a unit of time equal to one Billion (10⁹) years. It is commonly used in scientific disciplines such as Cosmology to signify extremely long time periods in the past. For example, the formation of the Earth occurred approximately 4.55 Ga (4.55 billion years) ago. As is clear from the notation, billion as used here is on the short scale.

See also

• Before Present
• Bya
• Geologic time scale
• Gya
• mya