Biodiversity

Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (genetic variability), species (species diversity), and ecosystem (ecosystem diversity) levels. Biodiversity is not distributed evenly on Earth; it is usually greater in the tropics as a result of the warm climate and high primary productivity in the region near the equator. Tropical forest ecosystems cover less than 10% of Earth's terrestrial surface and contain about 50% of the world's species. There are latitudinal gradients in species diversity for both marine and terrestrial taxa. Marine coastal biodiversity is highest globally speaking in the Western Pacific ocean steered mainly by the higher surface temperatures. In all oceans across the planet, marine species diversity peaks in the mid-latitudinal zones. Terrestrial species threatened with mass extinction can be observed in exceptionally dense regional biodiversity hotspots, with high levels of species endemism under threat. There are 36 such hotspot regions which require the world's attention in order to secure global biodiversity.

Since life began on Earth, five major mass extinctions and several minor events have led to large and sudden drops in biodiversity. The Phanerozoic aeon (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 non-avian dinosaurs.

The period since the emergence of humans has displayed an ongoing biodiversity loss and an accompanying loss of genetic diversity. This process is often referred to as Holocene extinction, or sixth mass extinction. During the last century, decreases in biodiversity have been increasingly observed. It was estimated in 2007 that up to 30% of all species will be extinct by 2050. Habitat destruction for the expansion of agriculture and the overexploitation of wildlife are the most significant drivers of contemporary biodiversity loss, and climate change also plays a role.