Mass Extinctions
A MASS EXTINCTION is a relatively brief period when a HUGE percentage of species die out. Earth has had FIVE major mass extinctions in the last 540 million years. Each reshaped life's trajectory. After each, surviving lineages diversified into new forms — including, eventually, us. Many scientists argue we're currently in a SIXTH mass extinction caused by humans.
The Big Five. ORDOVICIAN-SILURIAN (~445 mya): glaciation killed ~85% of species. LATE DEVONIAN (~370 mya): ocean changes killed ~75%. PERMIAN-TRIASSIC (~252 mya): "The Great Dying" — ~96% of species lost, the worst extinction ever, possibly from massive volcanism. TRIASSIC-JURASSIC (~201 mya): cleared the way for dinosaur dominance. CRETACEOUS-PALEOGENE (~66 mya): asteroid impact killed all non-avian dinosaurs and ~75% of species. Each extinction led to evolutionary booms in survivors.
The Permian-Triassic extinction (~252 million years ago) killed about ___ % of species — the WORST mass extinction ever.
Are we in a sixth? Many biologists say YES. Current extinction rates are 100-1,000x background levels. Habitat loss, climate change, pollution, invasive species, and overharvesting all contribute. The "Holocene extinction" or "Anthropocene extinction" (depending on the term) is well underway. Unlike past mass extinctions, this one has a known cause: us. And unlike past ones, we have the choice to slow or stop it.
Reflect
Look up the IUCN Red List. Pick a "critically endangered" species. Read about why it is at risk. Each species lost is a unique ~3.5-billion-year-old lineage going extinct on our watch.
Mass extinctions remind us that life is resilient — but not invincible. Past ones were natural. The current one is something we can choose to change.
Want to keep learning?
Sign up for free to access the full curriculum — all subjects, all ages.
Start Learning Free