With the end of the Ordovician period came the mass extinction event. However, life managed to survive and flourished again in the Silurian period. Despite being the shortest one in the Paleozoic era, it comes with a few remarkable changes.
The End of Mass Extinction Event
As we discussed, the exact cause of the mass extinction event remains unknown. However, we now have a way to explain the end of it. It comes with the hypothesis, that Earth froze, and due to glaciation, sea level dropped dramatically. By the end of Ordovician ice started melting, and sea level rose again. Life started to develop again, creating more biodiversity among taxa that survived. Life did not fully recover, and the ecosystems of the Silurian period were way less complex than in the previous periods. However, this extinction event did not have such an ecological impact as the ones that were yet to come.
After mass extinction life started to develop again. The most important change is the appearance of vascular plants. Those plants conduct water and other substances through specialized tissues. That quality is the main reason they can survive the land, which is why we sometimes call them land plants. On the fauna’s front, bony fished covered with bony scales appeared, and sea scorpions ruled in the northern waters. Some familiar animals, like mollusks and leeches, evolved. Besides, corals often engage in symbiosis with sponges, just like they do today. Trilobites were still hanging in there and developing. However, some animals finally managed to adapt to the terrestrial condition. The Middle Silurian brings us land millipedes, maybe even myriapods and ancestors of arachnids. However, food chains remained simple during the entire period, never fully recovering from the mass extinction.
Silurian Changes on Earth
In general, Silurian was a moment of climatic stabilization between Ordovician glaciation, and hot Devonian. We already said that sea levels rose again, so did the levels of CO2 in the atmosphere. As a result, Earth started warming, the glaciers almost disappeared, and violent storms appeared quite often. Due to unstable CO2 levels, a few minor extinction events occurred. On a geological level, almost flat Gondwana covered the south, with some island chains, and minor landmasses. The north of the globe was covered with a huge ocean.- Panthalassa. Moreover, due to plate tectonics movement, some minor collisions caused several small mountain chains to appear.
The end of the Silurian period
The end of periods we discussed so far all came with big climatic changes and mass extinction events. However, The Silurian-Ordovician boundary is an exception here. Scientists argued over it for a long time. Finally, the Barrandian area in the Czech Republic was chosen to be a place used as a physical definition of the boundary. Nowadays, places around the world are compared to that place, to help determine the time they belong to. There are many other Global Boundary Stratotype Sections and Points that define other significant boundaries on the Geological Time Scale. We need to remember, that time scales are artificially created, though scientists try to be as precise as possible. The existing system enables us to navigate through the history of life and mark important events. Most importantly, it brings similar periods together, enabling us to see patterns.
Silurian Period Evidence
The most important piece of the Silurian period evidence is probably the oldest known fossil of land plants. There are also many fossilized pieces of mosses, which impact on Earth started rising in the Devonian period. There are many fossils of ever-developing trilobites. broken pieces of shells indicate that many storms appeared. Other pieces of evidence also included fishes like Acanthoids, and sea scorpions- Eurypterids. Lots of those were found nearby the East Coast in the US.
Previous In Series: The Ordovician Period (Era of First Vertebrates)
I hope reading that article helped you learn about the Silurian period. If you enjoyed reading please share with your family and friends. We are now halfway through the Paleozoic era, in the next article we will discuss the Devonian period. Stay tuned, and if you have any questions feel free to write an email. You can find my address in the ‘Our Team’ section of the page.