, a contraction
of "biological diversity
," generally refers to the variety and variability of life on Earth. One of the most widely used definitions defines it in terms of the variability within species, between species and between ecosystems. It is a measure of the variety of organisms present in different ecosystems. This can refer to genetic variation
, ecosystem variation, or species variation (number of species) within an area, biome
, or planet. Terrestrial biodiversity tends to be greater near the equator, which seems to be the result of the warm climate
and high primary productivity
. Biodiversity is not distributed evenly on Earth. It is richest in the tropics
. Marine biodiversity tends to be highest along coasts in the Western Pacific, where sea surface temperature
is highest and in the mid-latitudinal band
in all oceans. There are latitudinal gradients in species diversity. Biodiversity generally tends to cluster in hotspots, and has been increasing through time, but will be likely to slow in the future.
The number and variety of plants, animals and other organisms that exist is known as biodiversity. It is an essential component
of nature and it ensures the survival of human species by providing food, fuel, shelter, medicines and other resources to mankind
. The richness of biodiversity depends on the climatic conditions and area of the region. All species of plants taken together are known as flora and about 300,000 species of plants are known to date. All species of animals taken together are known as fauna which includes birds, mammals, fish
, reptiles, insects, crustaceans, molluscs, etc.
Rapid environmental changes typically cause mass extinctions. More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be extinct
. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. More recently, in May 2016, scientists reported that 1 trillion
species are estimated to be on Earth currently with only one-thousandth of one percent described. The total amount of related DNA
base pairs on Earth is estimated at 5.0 x 1037
and weighs 50 billion tonnes. In comparison, the total mass of the biosphere
has been estimated to be as much as 4 TtC (trillion tons of carbon
). In July 2016, scientists reported identifying a set of 355 genes from the Last Universal
(LUCA) of all organisms living on Earth.
The age of the Earth is about 4.54 billion years old. The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago, during the Eoarchean Era after a geological crust started to solidify following the earlier molten Hadean Eon. There are microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia. Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old meta-sedimentary rocks discovered in Western Greenland. More recently, in 2015, "remains of biotic
life" were found in 4.1 billion-year-old rocks in Western Australia. According to one of the researchers, "If life arose relatively quickly on Earth .. then it could be common in the universe
Since life began on Earth, five major mass extinctions and several minor events have led to large and sudden drops in biodiversity. The Phanerozoic eon (the last 540 million years) marked a rapid growth in biodiversity via the Cambrian explosion
—a period during which the majority of multicellular phyla first appeared. The next 400 million years included repeated, massive biodiversity losses classified as mass extinction events. In the Carboniferous, rainforest collapse
led to a great loss of plant and animal life. The Permian–Triassic extinction event, 251 million years ago, was the worst; vertebrate recovery took 30 million years. The most recent, the Cretaceous–Paleogene extinction event, occurred 65 million years ago and has often attracted more attention than others because it resulted in the extinction of the dinosaurs.
The period since the emergence
of humans has displayed an ongoing biodiversity reduction and an accompanying loss of genetic diversity
. Named the Holocene extinction, the reduction is caused primarily by human impacts, particularly habitat destruction
. Conversely, biodiversity impacts human health in a number of ways, both positively and negatively.
The United Nations designated 2011–2020 as the United Nations Decade on Biodiversity.