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Myr

Myr, short for million years, is a unit of time equal to 1,000,000 years. It is used in geology, paleontology, climatology, astronomy, and related fields to express durations and ages on long timescales. The unit is conventional rather than SI; it is often used alongside Ma (megaannum) and Ga (gigaannum). Myr is used both to denote durations (for example, “the interval lasted about 120 Myr”) and to express ages of rocks, fossils, or events relative to the present (“65 Myr ago”). When used without “ago,” Myr typically functions as a duration or age measurement anchored by a reference frame rather than a calendar date.

Earth’s age is about 4.54 Ga, i.e., roughly 4,540 Myr. On astrophysical and planetary timescales, processes such

See also: Ma (megaannum), Ga (gigaannum), ka (kiloannum).

as
star
formation
or
planetary
evolution
are
frequently
described
in
Myr.
The
range
of
relevance
spans
tens
of
millions
to
hundreds
of
millions
of
years.
The
use
of
Myr
helps
avoid
long
strings
of
seconds,
years,
or
other
units
when
discussing
very
large
times.