The Silurian period was originally named in the 1830s by the English geologist Sir Roderick Impey Murchison after the Silures, an ancient Celtic tribe that lived along what is now the Welsh-English border. The most significant evolutionary development of the Silurian period was the arrival of the first true terrestrial ecosystem.
Tectonics and Paleoclimate
During the early Paleozoic, the continents were clustered around the equator, with Gondwanaland continuing its slow southern drift. Siberia, Laurentia, and Baltica converge at the equator and by the end of the Silurian, had began to raise mountains and forge the new super continent of Laurussia. The Earth entered a long warm greenhouse phase with latitudinal variations in climate similar to those of today including presence of glaciers in the higher latitudes. Regions of marked aridity occurred within 40o of the Silurian equator. Warm shallow seas covered much of the equatorial land masses.
The first fossil records of vascular plants (e.g., Cooksonia), land plants with tissue that carries food, appeared in the Silurian period. They were simple plants that had not developed separate stems and leaves.
The Silurian was host to a major invertebrate recovery from the Ordovician extinction. The high sea levels and warm shallow continental seas provided a hospitable environment for marine life of all kinds. Brachiopods (e.g., Pentamerids, Rhynchonellids, Atrypidids) are the most common hard-shelled organisms making up 80% of the total species. Planktonic graptolites remain common and diverse. Tropical reefs, which were formed by tabulate and rugose corals, stromatoporoid organisms, bryozoa, and calcareous algae, are common in the shallow seas. Trilobites, cephalopods, gastropods, and echinoderms roam the seas. The Trilobites are however on the decline, the Trinucleids and Asaphids have disappeared, and the Encrinids and Illaenids will die out before the end of the period. Jawless fish, eurypterids, xiphosurids, and sea scorpions invade brackish and fresh water sources for the first time in Earth’s history. By the end of the period the first jawed fish appeared but they remain relatively insignificant. Rhyniophytes, myriapods, arachnids, and centipedes appear on land, the first terrestrial animals known from fossil deposits.
Meteorite Impacts on Earth
I included a list of meteorite impacts relevant to this time period as a point of reference since many of the explanations for mass extinctions throughout Earth’s history include meteorite impact(s) as a possible cause. The meteorite impact information below was obtained from the ‘Earth Impact Database’ maintained by the Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick, Canada ( www.passc.net/EarthImpactDatabase).