Life in the Palaeozoic era
The Palaeozoic era lasted from about 539 to 252 million years ago (about 287 million years) and has six periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. In the Cambrian many animal phyla appear within a short geological time (the “Cambrian explosion”): animals with skeletons and shells, trilobites, arthropods, molluscs and echinoderms, which fossilise well. In the Silurian the first land plants (early vascular plants) and jawed fishes appeared. In the Devonian large plants with conducting tissues, the first seed plants and transitional forms between fish and land vertebrates (Tiktaalik) and the first four-limbed vertebrates – tetrapods (about 370 million years ago; for example Ichthyostega) – appeared, descended from lobe-finned fishes. The Carboniferous had warm, wet swamp forests of tree ferns, horsetails and club mosses; their remains became coal. Oxygen in the air was high, so very large insects flew. At the end of the Carboniferous the amniotes appeared – reptiles whose eggs have a shell or membranes and can be laid on land. At the end of the Permian (about 252 million years ago) came the biggest mass extinction in Earth’s history: 80–90 per cent of marine species vanished and trilobites died out completely. Large volcanic activity, climate change and falling ocean oxygen are given as causes.
“Journey through the layers”: six paper layers for the six periods on the wall; groups attach a card for each layer with a typical plant, animal and aromorphosis.