When was the Cretaceous Period?

The Cretaceous period was long long ago. It extended from 140 million years ago until 65 million years ago. It was the last period of the mesozoic era, often called the 'Age of the Dinosaurs'. The end of the cretaceous was marked by a mass extinction event where many species of marine and land animals, including dinosaurs became extinct as well as the majority of land plants.

There are 5 great extinction events in the geological record and the dramatic ending of the cretaceous is the last of them. There are many theories and much controversy, which I will keep away from (at least for the moment). I will leave the last word to Tim Flannery in his book "We are the Weather Makers : The story of Global Warming"

The last time the earth was afflicted (*) was 65 million years ago, when every living thing weighing more than 35 kilograms, and the vast number of smaller species, was destroyed

(* he is talking about mass extinctions)

Aren't we humans all larger than 35 kg, I know I am!

What was the Cretaceous like?

I think of the cretaceous period as a time of luxuriant abundance. Tropical rain forest probably covered at least 10% of the land mass, and that land mass had been significant reduced. Many continental areas where covered by shallow seas (at least in the early cretaceous). Australia was almost half covered by such shallow seas, covering the Great Artesian Basin, the Murray Basin, Ecula Basin and Canning Basin. It is also clear that sea levels fell dramtically in the late cretaceous.

The climate was certainly hotter (there were no permanent polar ice caps) and wetter (higher humidity and possibly regular rain) but the climate may have been more benign than today. Without a strong temperature and pressure gradient (from the equator to the poles) to drive currents in the oceans and winds in the atmosphere. Weathering of the surface rocks was deep and in the few places we see that surface preserved the soils show hydromorphic (waterlogged) structure and are commonly laterites and latsols (tropical soil types). Plants where abundant but in the early cretaceous there where no flowers. Still there here massive forests with diverse flora. The angiosperms (flowering plants) evolved and spread quickly in the late cretaceous help by the increase range of insects species and particularly bees.

Ref: The Paleogeographic map is from "The Geological Evolution of Australian and New Zealand" Brown D.A; Campbel K.S.W & Crook K.A.W, Perggamon Press

The Victorian landscape in the Early Cretaceous.

There are mountain ranges on both sides of the central rift valley. The streams flowing out of these ranges have built alluvial fans along the foothills. Volcanoes are active in the distance. Eruptions of these volcanoes supplied the ash and cinders deposited by the large braided river system flowing through the rift valley.

Growing on the hills are tall pine trees (1) and shorter pentoxylalean trees (2), with a small plant-eating dinosaur (3) running underneath them. It is mid-summer, so the snow on the mountains has all melted. After the flooding caused by the snow melt, the water levels in the braided river system have dropped. There are occasional tree ferns (4) on the sandbanks between the river channels. Clumps of Phyllopteroides ferns (5) are growing on the banks of the channels.

Extract from a GSAV (Geological Society of Australia, Victoria Division) booklet 'Geological History of Victoria'. Unfortunately this booklet appears to be out of print.