Mass Extinctions

“Life's history contains bottlenecks where entire branches of the evolutionary tree disappeared.”

01 / PLAINLY

What it means, plainly

A mass extinction is a geologically brief interval of global biodiversity loss far above the background rate.

02 / CONTEXT

A little more

The fossil record documents five especially large crises with different or combined causes: impacts, volcanism, warming, oxygen loss, and ocean change. Survival depends on ecology, geography, and chance; it does not make surviving organisms universally superior.

03 / WHY IT MATTERS

Why it matters

It shows how planetary disruptions reorganize ecosystems and how dating, fossils, and geochemistry reconstruct causes millions of years later.

04 / EXAMPLE

A familiar example

At the Cretaceous–Paleogene boundary, an iridium-rich layer, shocked quartz, and the Chicxulub crater connect an impact with global change and extinction.

05 / LIMIT

What it does not mean

The five crises did not share one cause, eliminate all life, or make later mammal dominance inevitable.

06 / NOTICE

Notice it in your day

Choose one of the five extinctions and build a timeline with proposed cause, geological signal, fossil pattern, and major uncertainty.

FINAL NOTE

The idea worth keeping

Compare timing, pace, loss distribution, and several causal signals before attributing a crisis.

QUESTIONS / 02

Questions people still have

Were all mass extinctions caused by impacts?

No. Several are linked to volcanism and climate or ocean changes, and causes can combine.

Does survival demonstrate evolutionary superiority?

No. Crisis-relevant traits, location, and contingency matter without creating a universal ladder of superiority.