“So… what actually happened to the dinosaurs?”
Short answer: an asteroid the size of a city hit what’s now Mexico 66 million years ago, plunged the planet into “impact winter,” collapsed food webs, and wiped out most species—including all non-avian dinosaurs. Birds (which are dinosaurs) survived and kept going. stratigraphy.orgNSF – National Science Foundation American Museum of Natural History
Here’s what we know, how we know it, where scientists still argue, and why your backyard pigeons are tiny T. rexes with better manners.
The day the rock fell (and where it hit)
Around 66 million years ago, a ~10-km asteroid slammed into shallow sea along the Yucatán Peninsula, excavating the Chicxulub crater (now ~180–200 km across, with a preserved peak ring). The impact released unimaginable energy, lofted pulverized rock high into the atmosphere, triggered global tsunamis, wildfires in many regions, and set off the chain of events we call the Cretaceous–Paleogene (K–Pg) mass extinction. stratigraphy.orgpublications.iodp.orgAGU Publications
How do we know the timing? The International Commission on Stratigraphy pegs the K–Pg boundary at ~66.0 Ma; drilling into Chicxulub’s peak ring (IODP Expedition 364) and high-precision dating tie the crater to that boundary. stratigraphy.orgpublications.iodp.org
What you’d have seen (if you could have seen): a blast bright as a thousand suns, a wall of ocean racing outward, and then—far more deadly—the sky filling with dust and soot that turned day to deep twilight worldwide. Climate models and geologic evidence agree: photosynthesis crashed, temperatures plunged for months to years, and many ecosystems simply couldn’t bridge the gap. PNAS+1
The smoking guns (the evidence is layered in rock)
- Iridium spike: In 1980, Luis and Walter Alvarez’s team found a global layer rich in iridium—a metal rare in Earth’s crust but common in asteroids—right at the K–Pg boundary. That paper kicked off the modern impact story. Later work even found the iridium layer inside the Chicxulub crater, locking the timing to the boundary. SciencePMC
- Shocked quartz & glass spherules: Minerals deformed under extreme pressure and tiny glass droplets (tektites/spherules) blanket boundary rocks on multiple continents—classic fingerprints of a giant impact. LPI
- The crater itself: Geophysics identified Chicxulub in the early 1990s; Expedition 364 cored its peak ring, confirming impact mechanics and immediate tsunami/gravity-flow deposits. publications.iodp.org
- Megatsunami modeling: New global simulations show the impact generated an ocean-spanning tsunami; educational datasets from NOAA capture the same big picture for public outreach. AGU PublicationsScience On a Sphere
What killed so many things? (The “impact winter,” in plain English)
The rock didn’t need to hit every dinosaur. It needed to black out the sun.
Two lines of research have converged here:
- Soot from burning biomass & target rocks—the impact injected soot and aerosols high into the stratosphere, cutting sunlight and chilling the surface. Climate models show near-total darkness in places, shutting down photosynthesis for months. PNAS+1
- Fine silicate dust—the latest studies argue micron-scale dust lofted by the impact sustained the darkness long after the initial blast, keeping ecosystems starved of light. Astrophysics Data System
A 2025 study also suggests the sulfur release (long thought to drive extreme cooling) may have been lower than earlier models assumed, shifting the focus even more toward dust and soot blocking sunlight rather than sulfur alone. The upshot is the same: a light-starved planet and a fast, brutal food-web collapse. Natureastro.oma.be
Field evidence supports the climate whiplash: rapid cooling right after the impact, followed by longer-term environmental instability as the system lurched toward recovery. PNAS
Wait, wasn’t there also super-volcano activity?
Yes—the Deccan Traps in India were erupting around the same time. That giant flood-basalt event released CO₂ and SO₂, likely stressing climate and ecosystems before and after the impact. Some records (e.g., from Antarctica) show two pulses of biotic stress: one linked to Deccan volcanism, one to the impact. The current best reading is “both mattered,” with the asteroid as the fatal blow. Recent work continues to refine just how much each factor contributed. NaturePNAS
Who died, who didn’t—and why
- Gone: all non-avian dinosaurs; all pterosaurs; most large marine reptiles (e.g., mosasaurs); ammonites; huge losses in plankton and many plant communities. It was a three-quarters of species kind of day in Earth history. Science On a Sphere
- Survivors: birds (the only living dinosaurs), crocodilians, turtles, many mammals, lizards & snakes (with heavy losses), frogs, and a selection of hardy plants. Small size, flexible diets, aquatic or burrowing habits, and the ability to bridge a long, dark famine were advantages. In birds, evidence points to small-bodied, ground-dwelling, seed-eating lineages doing best as forests collapsed and light vanished. American Museum of Natural HistoryScienceDirect+1
How quickly did Earth bounce back?
“Quickly” in geology is thousands to millions of years. Some food webs crept back within decades to centuries as sunlight returned and soils stabilized; forests and reefs took much longer; large-bodied animals returned later still. But the ecological deck had been reshuffled: mammals diversified, birds radiated, and the Cenozoic story—the one that ends in us—began. (That reset is part of why the K–Pg event is such a pivot in evolutionary history.) NSF – National Science Foundation
Were dinosaurs already dying out?
Good question. There were background climate and sea-level shifts late in the Cretaceous, and scholars have argued about pre-impact trends for years. But recent modeling shows that without the asteroid, suitable dinosaur habitats persist and many lineages likely continue. In other words: stress was real; the rock did the job. PNAS
“Dinosaurs went extinct”—not quite
A pedant (hi) will remind you: birds are dinosaurs—the avian branch of the theropod family tree. When we say “dinosaurs went extinct,” we mean the non-avian ones. The rest are raiding your bird feeder. evolution.berkeley.eduAmerican Museum of Natural History
FAQ (short, straight, snippet-ready)
What exactly caused the extinction?
Asteroid impact at Chicxulub → dark sky from dust/soot → photosynthesis crash → food-web collapse, with Deccan volcanism likely adding background stress. Astrophysics Data SystemPNASNature
When did it happen?
~66.0 million years ago at the K–Pg boundary, per the official time scale. stratigraphy.org
How do we know it was an asteroid?
The iridium layer worldwide, shocked quartz, melted spherules, a matching crater, and drilling results from Chicxulub. SciencePMCpublications.iodp.org
How dark did it get? For how long?
Models show near-total darkness in many regions for months, with fine dust prolonging the dimming and deepening the ecological crisis. PNASAstrophysics Data System
Did the impact make giant tsunamis?
Yes—global-scale waves. (New simulations and NOAA outreach materials map the spread.) AGU PublicationsScience On a Sphere
Who survived, and why?
Birds (small, many seed-eating ground birds), mammals, crocodilians, turtles, etc.—traits like small body size, flexible diets, and refuge-friendly lifestyles helped. ScienceDirect+1
Dinosaur Resources
- ICS International Chronostratigraphic Chart (Dec 2024): the official 66.0 Ma boundary. stratigraphy.org
- IODP Expedition 364 (Chicxulub peak ring) summary: drilling the crater itself. publications.iodp.org
- Alvarez et al., Science (1980): the original iridium anomaly paper. Science
- Goderis et al., Sci. Advances (2021): iridium layer preserved inside the crater. PMC
- Bardeen et al., PNAS (2017): soot-driven darkness shutting down photosynthesis. PNAS
- Lyons et al., PNAS (2020): target-rock soot exacerbating global cooling/darkening. PNAS
- Şenel et al., Nature Geoscience (2023): fine dust sustaining the impact winter. Astrophysics Data System
- Rodiouchkina et al., Nature Communications (2025): lower sulfur contribution than assumed. Nature
- Petersen et al., Nature Communications (2016): Deccan volcanism + impact signals in Antarctica. Nature
- Range et al., AGU Advances (2022) and NOAA SOS (2023): global tsunami from the impact. AGU PublicationsScience On a Sphere
- Real Dinosaur pictures
- AMNH / UC Berkeley: birds are living (avian) dinosaurs. American Museum of Natural Historyevolution.berkeley.edu
- Chiarenza et al., PNAS (2020): dinosaur habitat modeling—asteroid impact required to explain losses. PNAS
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