Period· The columns of time

Cretaceous

143 Ma → 66 Ma

The Cretaceous, from 145 to 66 million years ago, is the longest period of the Phanerozoic: flowering plants spread, the climate reached its thermal maximum and an impact closed the era.

Longest period of the Phanerozoic, in which flowering plants spread, climate reaches its thermal maximum and an impact closes the Mesozoic era.

What the evidence shows

Its name comes from chalk, a rock made of plankton: coccolithophores, single-celled algae armoured in plates of calcite, abundant enough for their remains to form the white cliffs of northern Europe and comparable deposits on three continents. Between 94 and 83 million years there is no permanent ice, sea level reaches its maximum of the last half billion years, and the temperature difference between the tropics and the high latitudes remains below 14 degrees against about twenty today. Flowering plants diversify and become dominant, the date of their origin remaining the oldest controversy in botany. The period ends at 66 million years, when a body some ten kilometres across strikes the shallow sea off the Yucatan in the northern spring, a season established from the bones of fish killed on the day itself, while more than a million cubic kilometres of lava erupt in India on either side of the same boundary.

Bounds and conventions

Its top is among the sharpest limits on the chart, an iridium layer identifiable worldwide. Its base is not: at 143.1 million years it still has no golden spike. The origin of flowering plants remains open, with indisputable fossils around 125 million years, contested older candidates, molecular clocks reaching into the Jurassic, and a reading of the fossil record that now places several families there. The contribution of the Deccan Traps to the extinction remains debated, at least one phase having begun several tens of thousands of years before the impact.