Background extinction rate, also known as the normal extinction rate, refers to the standard rate of
extinction
Extinction is the termination of a kind of organism or of a group of kinds ( taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed ...
in Earth's
geological and
biological history before
humans
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
became a
primary contributor to extinctions. This is primarily the
pre-human extinction rates during periods in between major
extinction events.
Overview
Extinctions are a normal part of the
evolutionary process, and the background extinction rate is a measurement of "how often" they naturally occur. Normal extinction rates are often used as a comparison to present day extinction rates, to illustrate the higher
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from '' angular frequency''. Frequency is measured in hertz (Hz) which is ...
of extinction today than in all periods of non-
extinction events before it.
Background extinction rates have not remained constant, although changes are measured over
geological time, covering millions of years.
Measurement
Background extinction rates are typically measured in three different ways. The first is simply the number of species that normally go extinct over a given period of time. For example, at the background rate one species of bird will go extinct every estimated 400 years. Another way the extinction rate can be given is in million species years (MSY). For example, there is approximately one extinction estimated per million species years. From a purely mathematical standpoint this means that if there are a million species on the planet earth, one would go extinct every year, while if there was only one species it would go extinct in one million years, etc. The third way is in giving species survival rates over time. For example, given normal extinction rates species typically exist for 5–10 million years before going extinct.
Lifespan estimates
Some species lifespan estimates by taxonomy are given below (Lawton & May 1995).
References
Further reading
*
E. O. Wilson. 2005. The Future of Life. Alfred A. Knopf. New York, New York, USA
*C.Michael Hogan. 2010
''Edenic Period''. Encyclopedia of Earth. National Council for Science and Environment ed. Galal Hassan, ed in chief Cutler Cleveland, Washington DC
*J.H.Lawton and R.M.May (2005) Extinction rates, Oxford University Press, Oxford.
External links
{{DEFAULTSORT:Background Extinction Rate
Extinction
Temporal rates