Palaeozoic: Devonian

The Devonian Period of the Palaeozoic Era was only slightly shorter than the entire Cenozoic Era (63 million years as opposed to 65) and was a time of many ‘firsts’ in Earth history. The Devonian saw the explosive diversification of vertebrate life (e.g., new fish species that proliferated in both marine and freshwater environments) including the evolution of the first terrestrial vertebrates, the amphibians. In the oceans, the Devonian saw the evolution of the largest reef ecosystems in Earth history. Both plant and animal groups were rapidly evolving and invading the terrestrial realm, and in the Devonian the Earth’s first forests evolved with trees that towered some 30 metres high. Yet it is also in the Devonian that the Earth suffered one of its greatest biodiversity crises, one of the ‘Big Five’ mass extinctions of life, and it is in the Devonian that the entire climate of the planet switched from a hot greenhouse state to a cold icehouse phase. The Devonian System is named after fossiliferous marine strata exposed in Devonshire, southwest England. The English palaeontologists Adam Sedgwick (see Famous Geologists: Sedgwick) and Roderick Murchinson (see Famous Geologists: Murchison) first proposed that the fossils in Devon were younger than Silurian fossils, yet older than Carboniferous, in 1839. Subsequent stratigraphic work demonstrated that the Old Red Sandstone of Scotland and Wales, long thought to lie in the basal Carboniferous, was the non-marine facies equivalent of Devonian marine strata. The Devonian Period is divided into seven Ages, from oldest to youngest:....