Flowers, T. rex and an asteroid
Cretaceous
Mesozoic Era · 145 – 66 million years ago
The Cretaceous Period ran from 145 to 66 million years ago, making it the longest period of the Phanerozoic at roughly 79 million years. It was the final chapter of the Age of Dinosaurs, a hothouse world of high seas in which flowering plants spread across the land and the modern continents began to take shape.
It ended in one of the most dramatic moments in Earth's history. An asteroid about 10 kilometres across struck what is now Mexico, and in its aftermath roughly three-quarters of all species disappeared, clearing the stage for the rise of mammals.
Key facts
- Began
- 145 MaMillion years ago
- Ended
- 66 MaMillion years ago
- Duration
- 79 million years
- Era
- Mesozoic“Middle life”
- Global temperature
- ~24°CRoughly 22–27°C · today 14.5°C
- Plants on land
- Flowering plants
- Atmospheric CO₂
- ~800–1,500 ppm (roughly 3–5× pre-industrial; estimates vary)
- Oxygen
- Probably similar to or somewhat above today's 21%
- Sea level
- Peaked ~100–250 m above today (estimates vary)
- Continents
- Pangaea's fragments drifting apart; Atlantic widening
- Signature life
- Tyrannosaurus, Triceratops, mosasaurs, first flowers
- Began with
- A gradual transition — no major mass extinction
- Ended with
- Chicxulub impact; ~75% of species lost
Ages follow the International Chronostratigraphic Chart (ICS). Global temperatures are rough reconstructions after Scotese et al. (2021); ancient CO₂, oxygen and sea-level values carry large uncertainties.
Epochs of the Cretaceous
- Early Cretaceous145 Ma – 100.5 Ma
- Late Cretaceous100.5 Ma – 66 Ma
Continents and oceans
At the start of the Cretaceous the supercontinent Pangaea was already breaking up. South America and Africa pulled apart as the South Atlantic opened, India broke away from Gondwana and raced northwards, and Australia and Antarctica remained joined near the South Pole.
Sea levels were among the highest of the past half-billion years, perhaps 100 to 250 metres above today at their peak. Shallow seas flooded the continental interiors: the Western Interior Seaway stretched from the Gulf of Mexico to the Arctic and split North America into two landmasses, Laramidia in the west and Appalachia in the east, while much of Europe and North Africa lay under warm water.
In those clear, sunlit seas, trillions of microscopic algae called coccolithophores built tiny plates of calcium carbonate. Their remains piled up into thick beds of chalk, such as the White Cliffs of Dover, and gave the period its name, from the Latin creta, meaning chalk.
Climate and atmosphere
The Cretaceous was a greenhouse world. Carbon dioxide levels were several times higher than before the Industrial Revolution, there were probably no large permanent ice sheets for most of the period, and forests grew close to both poles. The warmest interval, around 90 million years ago, saw tropical sea surfaces that some studies estimate exceeded 35 °C.
Warm oceans hold less oxygen, and on several occasions large parts of the deep sea became starved of it. These oceanic anoxic events buried vast amounts of organic carbon in black shales, which later became some of the world's important oil source rocks. Temperatures cooled gradually during the last 20 million years of the period.
Life in the Cretaceous
Dinosaurs reached their greatest diversity in the Cretaceous, but the period's most lasting revolution was botanical. Flowering plants, or angiosperms, appeared early in the period and by its end dominated many landscapes, transforming the food webs of insects, dinosaurs and early mammals alike.
Giant dinosaurs
Some of the most famous dinosaurs lived in the Cretaceous: Tyrannosaurus and Triceratops in western North America near its very end, the sail-backed Spinosaurus in North African river systems, and titanosaurs such as Argentinosaurus, which may have reached 30 metres or more in length.
The first flowers
Fossils such as Archaefructus from China, about 125 million years old, record early flowering plants. Angiosperms spread rapidly, alongside pollinating insects such as bees, and by the end of the period relatives of magnolias, water lilies, palms and plane trees were widespread.
Monsters of the sea
Mosasaurs, giant marine lizards related to today's monitor lizards and snakes, became top predators of the Late Cretaceous oceans, with some exceeding 12 metres. They shared the seas with long-necked plesiosaurs, huge sharks and coiled ammonites.
Feathers and wings
Birds diversified alongside their feathered dinosaur cousins, many of which are beautifully preserved in China. Overhead flew the largest pterosaurs ever, including Quetzalcoatlus, whose wingspan is estimated at around 10 metres.
Timeline of key events
- 145 Ma
Cretaceous begins
The period opens quietly, without a major mass extinction, as Pangaea continues to break apart.
- 125 Ma
Jehol Biota flourishes
Volcanic lakes in north-eastern China entomb feathered dinosaurs, early birds, mammals and some of the earliest known flowers.
- 100.5 Ma
Late Cretaceous begins
The second epoch opens in a warm world of rising seas and spreading flowering plants.
- 94 Ma
Oceans lose their oxygen
A major oceanic anoxic event near the peak of Cretaceous warmth causes extinctions among marine plankton and other sea life.
- 68 Ma
Tyrannosaurus appears
Tyrannosaurus rex and Triceratops roam Laramidia during the last few million years of the period.
- 66 Ma
Chicxulub asteroid impact
A roughly 10-kilometre asteroid strikes Mexico, triggering the mass extinction that ends the Age of Dinosaurs.
How the Cretaceous ended
About 66 million years ago an asteroid roughly 10 kilometres wide hit the Yucatán Peninsula, leaving the Chicxulub crater, about 180 kilometres across. The impact triggered wildfires, tsunamis and a global veil of dust and sulphur aerosols that blocked sunlight and collapsed food chains. A thin layer of clay rich in iridium, a metal rare in Earth's crust but common in asteroids, marks this moment in rocks around the world.
Around three-quarters of species vanished, including all non-avian dinosaurs, pterosaurs, mosasaurs, plesiosaurs and ammonites. At the same time, enormous volcanic eruptions in India's Deccan Traps were pouring out lava and gases, and scientists still debate how much they added to the crisis. Birds, mammals, crocodiles and turtles were among the survivors.
Where to see Cretaceous fossils
The Hell Creek Formation of Montana and the Dakotas has yielded Tyrannosaurus, Triceratops and a record of the last days before the impact, while Dinosaur Provincial Park in Alberta is one of the richest dinosaur sites on Earth. In north-eastern China, the Jehol Biota preserves feathered dinosaurs, early birds, mammals and flowers in exquisite detail.
Mongolia's Flaming Cliffs produced Velociraptor, Protoceratops and the first widely recognised dinosaur eggs, and Morocco's Kem Kem beds are famous for Spinosaurus. In Britain, the Isle of Wight is known for Early Cretaceous dinosaurs, and the chalk cliffs of southern England are themselves a vast Cretaceous fossil.
Surprising facts about the Cretaceous
- Tyrannosaurus rex lived closer in time to us than to Stegosaurus: roughly 66 million years separate T. rex from today, but more than 80 million separate it from Stegosaurus.
- The Cretaceous lasted about 79 million years, longer than the entire time that has passed since it ended.
- Grasses already existed in the Late Cretaceous — tiny silica particles from grass have been found in fossilised dinosaur dung from India.
- Dinosaurs lived in northern Alaska, inside the Arctic Circle, where they had to cope with months of winter darkness.
- Chalk is made largely of the microscopic plates of single-celled algae; a single cubic centimetre can contain many millions of them.
- The oldest known bee, preserved in Burmese amber, is roughly 100 million years old, showing that pollinators were evolving alongside the first flowers.
Where it sits in deep time
The globe beside this article shows Earth 90 million years ago, reconstructed from the PALEOMAP paleo-elevation models. Step to another period and watch the continents drift into place.