What Is Extinction?
The permanent disappearance of every individual of a species from Earth. Once a species is extinct, it is gone forever — there is no coming back.
Extinction is a natural part of the history of life on Earth. Scientists estimate that over 99% of all species that have ever lived are now extinct. However, the rate at which species are disappearing today is far greater than the natural background rate, and human activity is largely responsible.
It is important to distinguish between two related terms:
The slow, natural rate at which species become extinct over geological time, estimated at roughly 1–5 species per year globally.
A period in Earth's history during which a very large number of species (more than 75%) disappear in a geologically short time — typically less than 2 million years.
Scientists believe we are currently in a sixth mass extinction event, sometimes called the Holocene extinction or the Anthropocene extinction, driven primarily by human activities.
Natural Causes of Extinction
Long before humans existed, species were going extinct due to natural processes. Understanding these helps us appreciate how extraordinary today's extinction crisis is.
1. Asteroid or meteor impacts
A large asteroid impact can throw dust and debris into the atmosphere, blocking sunlight, cooling the planet, and collapsing food chains. This is strongly linked to the end-Cretaceous mass extinction (~66 million years ago) that wiped out non-avian dinosaurs.
2. Volcanic activity
Massive, prolonged volcanic eruptions release huge amounts of gases including CO₂ and SO₂, altering climate and poisoning ecosystems. The end-Permian extinction (~252 million years ago) — the largest mass extinction — is linked to volcanic activity in what is now Siberia.
3. Climate change (natural)
Ice ages and natural warming cycles shift habitats, sea levels, and rainfall patterns. Species that cannot adapt or migrate fast enough may go extinct.
4. Competition and disease
Natural introduction of new competitors or pathogens can drive a species to extinction without any human involvement.
5. Sea level changes
Rising or falling sea levels can destroy coastal and shallow-water habitats, eliminating the species that depend on them.
Think of each species as a business. If market conditions change slowly, a business can adapt. But if a sudden economic crash hits (like an asteroid impact), even healthy businesses can collapse almost overnight.
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