HOME

TheInfoList



OR:

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 Endling, last individual of the species, although the Functional ext ...
in Earth's
geological Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other E ...
and biological history before
humans" \n\n\n\n\nThe robots exclusion standard, also known as the robots exclusion protocol or simply robots.txt, is a standard used by websites to indicate to visiting web crawlers and other web robots which portions of the site they are allowed to visi ...
became a primary contributor to extinctions. This is primarily the pre-human extinction rates during periods in between major
extinction event An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. I ...
s.


Overview

Extinctions are a normal part of the
evolutionary process Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation t ...
, 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 eq ...
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 The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochron ...
, 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