die and disappear someday. This is known as extinction. In most
cases, extinction is a means by which a new species arises. There
is debate over the pace of extinction. Generally, there are two
large types of extinction.
This is also
known as natural extinction. Background extinction refers to the
extinction that occurs naturally in the evolution process. 0.00003%
of species become extinct naturally according to fossil records.
This extinction has been occurring since the origin
of life on earth. During the ecological process, the natural
extinction occurs following the evolution of the species. If a species
cannot succeed in adapting to its surroundings it eventually becomes
extinct. Factors of background extinction include gradual changes
in temperature, humidity, predator-prey
relationships , and tectonic plate movements. David Raup estimates
that the average species stays around for 4 -22million years before
it becomes extinct and that 99.9 of all the species that have ever
existed are now extinct.
In mass extinctions,
large numbers of species become extinct each year for tens of thousands
to millions of years. Terrestrial biodiversity has experienced five
great mass extinctions during the past 500 million years. These
mass extinctions have been 20-60 million years apart and there have
also been shorter mass extinctions (loss of 15-24% of all species)
in between. A period of mass extinction is often regarded as having
a loss of 25-70% of all species. The extinction of the dinosaurs
is a fine example of mass extinction.
of Mass Extinction
over the causes of mass extinction. Some say that rapid climate
changes such as the ice age caused the extinction of many species,
and some say that other catastrophic events such as large volcanic
eruptions and meteorites impacts into the earth causes extinction.
Nevertheless, mass extinction which can be the bane of one species,
however, can become an opportunity for another. How, after five
mass extinctions, could there be such an immense amount of biodiversity
today? This fact can be explained by the concept of adaptive radiation.
are evidence of the earth's capability to regenerate biodiversity.
All mass extinctions have been followed by periods of recovery,
known as adaptive radiations. After almost every mass extinction,
numerous new species have evolved to fill new or vacated ecological
niches in the changed environment. The extinction of dinosaurs,
for example, was followed by an explosive rise of mammals. Fossil
records suggest about 10 million years or more are required for
adaptive radiations to rebuild biological diversity after a mass