The Devonian, when forests first rose and fish began crawling ashore
Around 400 million years ago the land was mostly bare, and the seas belonged to armoured fish. Over the next 60.7 million years, the Devonian saw the first forests, the first seed plants and the first four-limbed animals, before two waves of extinction wiped out most of the reefs that had thrived alongside them.
The period runs from 419.62 to 358.86 million years ago and takes its name from Devon in south-west England. In the 1830s geologists argued bitterly over the age of that county's rocks; in the Great Devonian Controversy, Roderick Murchison and Adam Sedgwick prevailed over Henry De la Beche and inserted a new period into the timescale. Nineteenth-century writers called it the Old Red Age, after the Old Red Sandstone of Britain, rock stained red by iron oxidised in near-desert conditions.
On land, spore-bearing plants spread widely, leaves and true roots appeared by the middle of the period, and the first forests took shape in the Frasnian stage beginning 382.31 million years ago. Those forests pulled carbon dioxide from the air and buried it in sediment, which may explain a cooling of about 5 degrees Celsius in the Middle Devonian. Tropical seas in the early part of the period averaged around 30 degrees. Myriapods, arachnids and early insects were already established ashore.
In the water, jawed fish diversified so much that the period earned the name Age of Fishes. Armoured placoderms dominated nearly every habitat, sharks multiplied, and the first ammonoids evolved from nautiloids. In warm, oxygen-poor inland lakes, some lobe-finned fish developed lungs and sturdy fins that became limbs, and the first tetrapods appear in the Famennian, the final stage.
The Late Devonian extinction, beginning about 375 million years ago, destroyed most reef systems, most jawless fish and nearly all trilobites. A second blow around 359 million years ago finished off the placoderms. Meanwhile Laurussia and Gondwana were drifting together, raising the Appalachians and beginning the collisions that would eventually form Pangaea.
Source: Devonian
