Time Periods

Dartmoor Origins

The part of our island we now call Dartmoor looked very different in the past: During the last four hundred million (400,000,000) years, it was sea, then mountains, was covered again by sea, then by warm tropical forest, and was frozen solid in the Ice Ages. Each of these eras has left its mark on the landscape of today.

400 million years ago, this area was covered by a warm sea; rivers carried sediment into it, which formed rocks (soft mudstone, brittle shale and others). Around 290 million years ago a massive upwelling of molten granite lifted the sea bed, creating a mountain range from the sedimentary rocks above. Combinations of water, heat, and pressure formed bands of minerals such as tin, china clay, lead and arsenic, as well as several other rare compounds; minerals valued by people, who have altered the landscape in the past and in our own time.

Between 270 and 200 million years ago the mountains were eroded by wind, periods of torrential rain, and extreme changes of temperature. These processes nearly uncovered the large mass of granite which defines Dartmoor’s rugged character. Reptiles slid through the vegetation; there were only a few trees, some of which were huge conifers.

Dinosaurs ruled the world during the Jurassic and Cretaceous periods, 201-66 million years ago.

200-145 million years ago: Dartmoor’s vegetation changed to abundant forests of conifers, gingkos and fern-like trees (cycads); small dinosaurs scurried beneath the branches.

145-65 million years ago: The area flooded, creating a shallow sea. Huge marine reptiles, such as plesiosaurs and ichthyosaurs, lived here. It was also home to millions of microscopic sea creatures whose bodies, falling to the bottom of the sea, made a layer of chalk.

 The mammals appear on Dartmoor

From 65 to 2 million years ago, as sea levels dropped and the dinosaurs vanished, animals and plants more familiar to us (like mammals and flowering plants) evolved, and a jungle developed in the near-tropical climate. Erosion wore away the thin covering of chalk, exposing the ancient granite beneath. The Teign and Dart rivers began to cut their courses. 2 million years ago Dartmoor was an island; the layers of rocks shifted, tilting and cracking, creating the formations we see around us.

Ice ages and humans

In the last 2 million years, there were four Ice Ages, a series of fluctuations from cold, through temperate, to warm periods. During these cold periods the huge glaciers didn’t quite reach Dartmoor; however the edge of the ice sheet came as close as Bristol, meaning that the ground here was often frozen. In between glacial periods, the climate was warmer than it is now, and lions, hyenas, rhinoceros, and elephants sauntered through deciduous woods alongside beaver and wolf.

The last Ice Age ended 12,000 years ago. Trees thrived, with large oak woods covering Dartmoor.

In the milder climate, prehistoric people and natural forest fires gradually cleared the woodland. This clearance created the treeless moorland we see today. The earliest inhabitants of the moor would have included Neanderthals, who lived in Europe (including Britain) alongside Homo sapiens for thousands of years. Their stone tools have been found in Kents Cavern, near Torquay.

Bogs with their deposits of peat formed from about 8,000 years ago in even wetter conditions than today. Thousands of tiny plants, identifiable under the microscope, make up this organic layer, over 7 metres thick in places.

Dartmoor’s landscape looks like an unchanging environment to the casual visitor, but seen from the perspective of thousands of millennia its geology can be seen as an ongoing dynamic process; a time traveller would view the current moorland as a snapshot in this succession of different sea levels, climatic shifts and varying ecologies. Who knows what Dartmoor’s far future holds for it?

 DNPA factsheet - http://www.dartmoor-npa.gov.uk/learningabout/lab-printableresources/lab-factsheetshome/lab-geologylandforms

Image from ian shiell [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons