A mass extinction is usually defined as a loss of about three quarters of all species in existence across the entire Earth over a “short” geological period of time. Given the vast amount of time since life first evolved on the planet, “short” is defined as anything less than 2.8 million years.
Causes of Extinction
The single biggest cause of extinction today is habitat loss. Agriculture, forestry, mining, and urbanization have disturbed or destroyed more than half of Earth’s land area. Other causes of extinction today include:
- Exotic species introduced by humans into new habitats. They may carry disease, prey on native species, and disrupt food webs. Often, they can out-compete native species because they lack local predators.
- This threatens their survival and the survival of species that depend on them.
- Global climate change, largely due to the burning of fossil fuels. This is raising Earth’s air and ocean temperatures. It is also raising sea levels. These changes threaten many species.
- Pollution, which adds chemicals, heat, and noise to the environment beyond its capacity to absorb them. This causes widespread harm to organisms.
- Human overpopulation, which is crowding out other species. It also makes all the other causes of extinction worse.
The study analysed 29,400 species of terrestrial vertebrates and determined which of these are on the brink of extinction because they have fewer than 1,000 individuals. Out of the studied species, they concluded that over 515 of them are near extinction, and that the current loss of species, which is based on the disappearance of their component populations, has been occurring since the 1800s.
According to the Center for Biological Diversity, when species go extinct, the impact can be tangible such as in the form of a loss in crop pollination and water purification. Further, if a species has a specific function in an ecosystem, the loss can lead to consequences for other species by impacting the food chain.
The study warns that the effects of extinction will worsen in the coming decades as the resulting genetic and cultural variability will change entire ecosystems. “When the number of individuals in a population or species drops too low, its contributions to ecosystem functions and services become unimportant, its genetic variability and resilience is reduced, and its contribution to human welfare may be lost.