When Did Dinosaurs Go Extinct?

The extinction was geologically abrupt, but saying "all dinosaurs died exactly 66 million years ago" needs one important correction: birds survived. Birds are living dinosaurs, so what disappeared at the K–Pg boundary were the non-avian dinosaurs.

The Date: 66 Million Years Ago

Radiometric dating has allowed scientists to compare the age of the extinction boundary with the age of the Chicxulub impact with remarkable precision.

One study found that the impact and K–Pg extinction were synchronous within about 32,000 years, an extremely short interval on geological timescales. That does not mean every individual dinosaur on Earth died on the same day. It means the impact and biological crisis are effectively coincident at the resolution available from the geological record (Renne et al., 2013).

What Caused the Dinosaur Extinction?

The strongest evidence identifies the Chicxulub asteroid impact as the primary trigger of the end-Cretaceous mass extinction.

A worldwide boundary layer contains material associated with the impact, and its timing matches the extinction. Chicxulub itself is a roughly 180-kilometer-scale impact structure centered near Mexico's Yucatán Peninsula. A major review concluded that the global ejecta layer, crater evidence, extinction pattern and modeled environmental effects together support the impact as the trigger (Schulte et al., 2010).

Enormous eruptions were also occurring in India's Deccan Traps around this general interval, so scientists have investigated whether volcanism caused or intensified the extinction. High-resolution records indicate that major volcanic outgassing began before the impact, whereas the abrupt mass extinction and major carbon-cycle disruption coincide with Chicxulub. The best-supported interpretation is that the impact was the main extinction trigger, while Deccan volcanism formed part of the broader environmental background (Hull et al., 2020).

What Happened After the Impact?

The immediate effects near the crater were catastrophic, but the global atmospheric consequences explain why an impact in one region could disrupt ecosystems worldwide.

Material blasted into the atmosphere reduced incoming sunlight and produced rapid cooling. Reduced light would also have damaged photosynthesis, destabilizing food webs from plants and plankton upward. Crater-core evidence supports a severe post-impact environmental crisis involving atmospheric aerosols and diminished photosynthesis.

The exact recipe of this "impact winter" remains an active research topic. Studies have examined contributions from sulfate aerosols, soot and fine silicate dust, and newer work has revised estimates of how important some components were. The broad conclusion, a rapid impact-driven global environmental crisis, is strong, while the precise relative contribution of each material remains uncertain.

Did All Dinosaurs Go Extinct?

No. Every known non-avian dinosaur lineage disappeared at the K–Pg boundary, but some avian dinosaurs survived. Those survivors gave rise to the enormous diversity of birds alive today.

Survival itself was selective. Research on fossil plants and early birds indicates that the impact caused widespread forest destruction and that the earliest surviving crown-bird lineages were associated with ground-dwelling ecologies rather than tree-dependent ones. The details of exactly why particular bird lineages survived are still being refined (Field et al., 2018).

You can explore the final age of the dinosaurs on the interactive Pangea Map and move the timeline to the end of the Cretaceous at 66 Ma.

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