The third period of geological time in the Palaeozoic era from about 440 to 395 million years ago, during which there is the first evidence of the invasion of the land by plants and animals. Thick-walled spores with triradiate markings have been found. The fossil Cooksonia from the Upper Silurian with its slender branched stem, lack of lateral appendages, terminal sporangia, and cutinized spores, resembles Rhynia, a psilopsid from the Rhynie chert. The fossil Nemaphyton resembles the stipe of a seaweed. Marine life was similar to that of the Ordovician, and the climate is thought to have been uniformly warm, becoming drier towards the end of the period. See geological time scale. |
