kiloannum

Kiloannum, abbreviated ka, is a unit of time equal to 1,000 years. It is used to express durations and ages on geological and archaeological timescales, where multiple millennia are involved.

Origin and usage: The term combines kilo- (1000) with annus (Latin for year). In scientific writing, ka is commonly used with the concept of "present" as a reference. In many contexts, ka is paired with "before present" (BP), which is anchored at 1950 CE. For example, 2.3 ka BP means 2,300 years before 1950, corresponding to about 350 BCE. Some authors, however, simply use ka to denote thousands of years ago without explicit BP, understanding the reference as "as of now."

Other notations: kyr (kiloyears) is another widely used unit for thousands of years and is sometimes preferred when avoiding the BP convention. For longer periods, megaannum (Ma) and gigaannum (Ga) are used, with analogous conventions (e.g., MaBP, GaBP, kyr).

Examples: The end of the last glacial period is dated to about 11–12 ka in many records, and the Last Glacial Maximum is near 21 ka. Radiometric dating and stratigraphy commonly report ages in ka or Ma.

See also: kyr, Ma, Ga, BP.