Silurian
In Geological time, the Silurian period is the third period of the Paleozoic era. It started 443.8 million years ago and ended 419.2 million years ago, extending from the ending of the Ordovician period to the beginning of the Devonian period. During this period, continents' highlands were much lower and sea level was rising. Sea level rose drastically as the huge glacier from the Late Ordovician ice age melted.
The immediate changes in climatic conditions permitted many faunal groups to recover from the extinction of Late Ordovician times. Large expanses of different continents became flooded with shallow seas, and mound-type coral reefs were common. Fishes were extensive. Vascular plants began to take over coastal lowlands during this period whereas the continental interiors became infertile.
When Did the Silurian Period Start?
The Silurian period was the period from the end of the Ordovician period, at about 443.3 million years ago, to the beginning of the Devonian period, 419.2 million years ago. The Silurian period is considered to be the shortest period of the Paleozoic Era.
Silurian Period Significant Events
Life on Land
It was during this period that the first life came about from water and colonized the land. Increased ozone from photosynthetic water plants provided protection from the ultraviolet rays, making the terrestrial environment friendly to those organisms that could prevent desiccation.
First Vascular Plants
The first plant with an internal vascular channel was seen in Silurian period. Plants were not able to transfer food and gases to other parts of the structure, allowing a considerable amount of increase in size.
First Insect
The first insect seen in the Silurian period, was probably the first animal to come out of water.
First Jawed Vertebrates
The first fish with jaws appeared during the Silurian period, providing much better predictability and eventually giving rise to vertebrates known today.
Silurian Period Climate
The climate was much warmer during the Silurian period. This caused the melting of glaciers and sea levels to rise. Even though the sea level was rising, there was a place where the land was rising as well. This was due to the mountain building as the continental plates collided. In these places, the seas moved away from the coasts or evaporated from the shallow zones. Plants that had to live in coastal water had to live on land or die.
Fishes Gained Importance During the Silurian Period
Fishes gained much importance during the Silurian period. Most of the fishes were jawless at the beginning of the Silurian period. There were some earlier vertebrates, animals with soft cartilage bones. By the end of the Silurian period, animals with jaws and real bones were swimming in water. These animals soon would rule the seas.
Terrestrial
The most significant progressive development of this period was that of the first true terrestrial ecosystem.
The first fossil records of vascular plants, that is, land plants with tissue was of those which carries food, occurred during the Silurian period. The vascular plants were simple plants that had not developed individual stems and leaves.
By the middle of the Silurian period, a very simple early terrestrial community with simple plant producers, millipede herbivores, centipede and arachnid carnivores, worm detritivores, and fungal decomposers had developed.
The Mid-Late Silurian terrestrial biota included small plants along with the water's edge and arthropods such as trigonotarbids and myriapods. Fungi, nematodes, and perhaps earthworms were most likely present as well, although they did not leave a fossil record (except for possible fungi).
Did You Know?
The name Silurian originated from the Celtic from Whales.
During this period, the sea fluctuated between transgression and regression due to the climatic change and continental buildup.
The first fossil record of the Vascular plants appeared in the second half of the Silurian period.
FAQs on Silurian Period
1. How long did the Silurian Period last and where does it fit in the geologic timeline?
The Silurian Period lasted for approximately 24.6 million years, from about 443.8 million to 419.2 million years ago. It is the third period of the Paleozoic Era, following the Ordovician Period and preceding the Devonian Period. It is positioned between two major evolutionary events: the Ordovician-Silurian extinction that it followed and the subsequent 'Age of Fishes' in the Devonian.
2. What were the major geological and climatic events of the Silurian Period?
The Silurian Period was defined by significant environmental changes. The most important events include:
Climate Stabilisation: The period began as a major ice age from the late Ordovician was ending. As glaciers melted, the global climate became much warmer and more stable than in the preceding period.
Rising Sea Levels: The melting of vast ice sheets caused a substantial rise in global sea levels, which in turn created extensive, shallow continental seas ideal for marine life to flourish.
Mountain Building: Significant tectonic activity occurred, including the Caledonian orogeny. This mountain-building event helped form the foundations of mountain ranges in modern-day Scotland, Ireland, and Norway.
3. What was the dominant animal life like in the Silurian oceans?
Silurian oceans were teeming with life that diversified greatly after the earlier extinction event. Jawless fish (ostracoderms) became widespread, and crucially, the first jawed fish (acanthodians and placoderms) made their appearance. Coral reefs expanded significantly, creating complex ecosystems. The apex predators were the giant eurypterids, also known as sea scorpions, which were arthropods that could grow to over two metres in length.
4. What were the most significant developments in plant life during the Silurian Period?
The Silurian Period marks a pivotal moment in the history of life on Earth: the first colonisation of land by plants. The earliest terrestrial plants were very simple and small, lacking the complex root, stem, and leaf systems of modern plants. A key example is Cooksonia, one of the first known vascular plants. These pioneers grew close to water sources and began the critical, long-term process of transforming Earth's rocky landscapes.
5. Was the Silurian Period a time of mass extinction?
This is a common misconception. The Silurian Period itself was primarily a time of evolutionary recovery and diversification, not mass extinction. It began immediately following the Ordovician-Silurian extinction event, one of the most severe in Earth's history. Throughout the Silurian, life rebounded and new forms evolved to fill the empty ecological niches. The period did end with a series of smaller extinction events, but these were minor compared to the major event that started it.
6. How did atmospheric changes during the Silurian Period influence the evolution of life?
Atmospheric changes were critical for evolution during this time. The continued production of oxygen by marine algae led to a gradual rise in atmospheric O2 levels. This increase was a key enabler for two major evolutionary steps: it supported the development of more active and complex marine animals, including the first jawed predators, and it was a prerequisite for the survival of the first life on land. Early air-breathing invertebrates and the first simple land plants depended on this oxygen to exist outside of water.
7. How did the Silurian Period get its name?
The Silurian Period was named in the 1830s by the Scottish geologist Roderick Murchison. He was studying rock strata in Wales and its borderlands. He named the period in honour of the Silures, an ancient Celtic tribe that had inhabited that region and famously resisted the Roman invasion. This practice of naming geological periods after geographical locations or ancient peoples was a common tradition among early geologists establishing the geologic time scale.
8. How does the Silurian Period compare to the periods before and after it?
The Silurian Period serves as a crucial evolutionary bridge between the Ordovician and Devonian periods:
Compared to the Ordovician: The Ordovician ended with a harsh ice age and mass extinction. The Silurian represents the recovery phase, featuring a much warmer climate, higher sea levels, and the rapid diversification of marine life in new shallow-sea habitats.
Compared to the Devonian: The Silurian laid the essential groundwork for what would happen in the Devonian. While the first jawed fish and simple land plants appeared in the Silurian, they became dominant and vastly more complex in the Devonian, which is known as the 'Age of Fishes' and the era when the first true forests appeared.
