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The Origin of Land Plants

The oxygen content of the universe reached a threshold in the beginning of the Cambria and Carboniferous periods. The first lowland plants may have appeared about 400 million years ago in the Upper Silurian rocks. They had rudimentary root and vascular systems. Upland plants appeared during the Carboniferous and the Permian periods. They were dominant throughout the Paleozoic era and were huge in size resulting in the accumulation of biomass. The formation of soil may have occurred in the Devonian period when microorganisms would have penetrated deeper into soil come in contact with deep-seated root system in the late Carboniferous age. The upland plants began to increase in number in the Triassic age sand angiosperms (flowering plants) appeared in the Cretaceous period (about 100 million years ago).