The Day the Dinosaurs Died

TL;DR

The Chicxulub asteroid impact 66 million years ago triggered a cascade of disasters — heat pulses, acid rain, impact winter, and warming — that killed three-quarters of life on Earth.

Key Points

• 1.The Chicxulub impactor was over 10 km wide and struck the Yucatán Peninsula 66 million years ago. It blasted a 200 km wide, 30 km deep crater and was only discovered through seismic imaging and deep drilling — invisible from the surface under hundreds of meters of sediment.
• 2.The impact's immediate effects killed everything within hundreds of kilometers in minutes. A heat pulse of thousands of degrees expanded outward, followed by a shockwave that flattened trees, then a debris plume that rained molten rock spheres and shocked minerals across thousands of kilometers.
• 3.Spring timing of the impact is evidenced by fossilized fish at Tanis, North Dakota. Sturgeons and paddlefish were buried by earthquake-churned sediment within minutes of impact, with glassy spheres found inside their gills; bone analysis shows they died at the start of their growing season.
• 4.Tsunamis over 100 meters high in the Gulf of Mexico reached New Zealand within 24 hours. Wave evidence appears in chaotic coastal geological deposits worldwide; some end-Cretaceous sediment layers were entirely erased by 10-meter waves hitting distant coastlines.
• 5.An impact winter lasting at least a decade dropped global temperatures 15–20°C. Sulfate dust from vaporized anhydrite rocks and wildfire ash blocked sunlight so completely that plants couldn't photosynthesize for over a year, collapsing food webs from plants to herbivores to carnivores globally.
• 6.Acid rain from sulfuric compounds dissolved shells and poisoned soils and oceans for years. Over 90% of coccolithophore algae went extinct; fossil sites show shelled animals like snails and clams completely absent, possibly dissolved before fossilization or prevented from forming shells at all.
• 7.A post-winter greenhouse phase followed as 1.5 trillion tons of CO₂ warmed the planet ~2°C above pre-impact levels. Carbon from vaporized limestone lingered far longer than soot, causing ocean acidification that killed ammonites, belemnites, and reef corals; this warming lasted tens of thousands of years.
• 8.Recovery took millions of years: mammals didn't reach housecat size again until 100,000 years post-impact, and large herbivores (over one tonne) didn't return for 25 million years. The first signs of ecosystem recovery appeared 300,000 years later; five million years after impact, early tropical rainforests like Colombia's hosted giants like Titanoboa.