Ordovician
During the Ordovician, Life expanded tremendously in diversification and multiplicity. There existed a wide range of reef complexes in the tropics. The early Ordovician had been considered to be quite warm, at least in the tropics.
Throughout the time of the Ordovician period, part of the Paleozoic era, a plentiful variety of marine life prospered in the vast seas and the first primitive plants started to occur on land—prior to the second-largest mass extinction of all time terminated the period.
Age of Invertebrates
The Phanerozoic is classified into 3 eras i.e.:
the Paleozoic (550 to 250 million years ago),
the Mesozoic (250 to 65 million years ago)
Cenozoic (65 million years ago to the present)
The Paleozoic has been known to be the Age of Invertebrates due to the rapid development of invertebrate animals during that time.
Invertebrate
Invertebrate life became growingly complex and diverse through the Ordovician. Both calcareous and siliceous sponges are well recognized; among other types, the stromatoporoid first occurred in the Ordovician. Even the Tabulata (platform) and rugosa corals (horn corals) occurred first in the Ordovician, the solitary or horn corals being particularly distinguishing. Brachiopods (lamp shells) and Bryozoans (moss animals) have been a dominant component of many accumulations. Molluscs were also quite common and included the bivalves, chitons, cephalopods, scaphopods (tusk shells), rostroconchs (single-shelled molluscs), gastropods, and monoplacophorans (limpet-shaped, segmented molluscs).
Most of the planet’s landmasses combined to create the supercontinent of Gondwana, which included the continents of Africa, South America, Antarctica, and Australia. Gondwana floated along the south throughout the period, ultimately establishing on the South Pole. The landmass that progressed towards being North America was combined into the supercontinent of Laurentia, which was isolated from Gondwana by the narrow Iapetus Ocean.
Mass Extinction of Ordovician
Despite the extreme expansion of life during the Ordovician Period, there has been a devastating mass extinction of organisms at the end of the Ordovician. This extinction has been chronicled to be of the greatest mass extinction ever in Earth History with over 100 families going extinct.
Reason of Extinction of Ordovician
There has been majorly 2 reasons for Ordovician going extinct:-
1. One belief was that it was the breakup and movement of the massive supercontinent into many splinters. However, modern biology makes us know that this would not possibly result in extinction; instead, it would give additional niche space for groups to expand into.
2. A greater cause is that the Earth cooled, especially the oceans where the majority of the organisms lived during the Ordovician period (Remember there are still no evidence of land plants and land organisms). All the extinctions took place in the oceans.
A pronounced extinction took place in the tropical oceans. This makes sense because if the oceans cooled off due to the development of a huge ice sheet over the south polar area, the organisms adapted to warmer tropical conditions would have limited options and feasible nowhere to migrate to. There would be restricted regions warm enough to harbour all the warm-favouring organisms. This is inclined to support the idea that cooling resulted in many of the extinctions.
Silurian Period
It is the expansion of life following the mass extinction of the Ordovician. the first land plants appeared during the Silurian Period. Once again expanded the Marine organisms in diversity following the extinction of many families in the Late Ordovician.
The Silurian was possibly comparatively warm even though pCO₂ (Partial Pressure of Carbon Dioxide) may have been lower. This is believed to be since there has been no large landmass over the South Polar Region through the Silurian period.
Devonian Period
Devonian fish were a common element of the marine biological communities. Particularly important organisms during the Devonian were the jawed fish.
The first fossil evidence of terrestrial trees and insects appeared from Devonian age rocks. The Devonian is quite warm and the climate is thought to have been very dry. Evidence of this emerges from large amounts of tropical-like reefs and evaporite (salt deposits).
In current times, for example, evaporites are only limited to the mid-latitude belt where dry sinking air appearing from the Hadley cells makes these regions dry. During the Devonian period, these evaporite deposits were observed well beyond 30 degrees north and south.
FAQs on Ordovician Period
1. What is the Ordovician Period and when did it occur?
The Ordovician Period is a major division of the Paleozoic Era in Earth's geologic timescale. It spanned from approximately 485.4 million to 443.8 million years ago, lasting for about 41.6 million years. It follows the Cambrian Period and is succeeded by the Silurian Period.
2. What is the Ordovician Period most known for?
The Ordovician Period is most famous for the Great Ordovician Biodiversification Event (GOBE), an evolutionary radiation where the diversity of marine life increased dramatically. This period saw the rise of many new groups, including trilobites, brachiopods, and the first jawless fish. It ended with one of the most severe mass extinctions in Earth's history.
3. What was the climate like during the Ordovician Period?
For most of the Ordovician, the climate was warm and tropical, with high sea levels creating vast shallow seas ideal for marine life. However, towards the end of the period, the climate cooled drastically. This led to a major ice age centered on the supercontinent Gondwana, which was then located over the South Pole.
4. What kind of animal life dominated the Ordovician seas?
Ordovician seas teemed with invertebrate life. The most dominant groups included:
- Trilobites: Diverse and abundant arthropods.
- Brachiopods: Shelled animals that became extremely common.
- Graptolites: Colonial animals that are important index fossils.
- Nautiloids: Early, straight-shelled relatives of modern squids.
- Crinoids: "Sea lilies" that formed underwater forests.
5. Did plants exist on land during the Ordovician Period?
Yes, the very first evidence of life on land appears in the Ordovician Period. While the continents were largely barren, fossil evidence suggests the presence of primitive, non-vascular plants, similar to modern liverworts and mosses. These early plants were small and confined to moist, coastal areas.
6. What was the Great Ordovician Biodiversification Event (GOBE)?
The Great Ordovician Biodiversification Event, or GOBE, was a period of rapid evolutionary radiation in marine life. Unlike the Cambrian Explosion which established the major animal body plans (phyla), the GOBE saw a massive increase in diversity at lower taxonomic levels like class, order, and family. This event fundamentally established the structure of Paleozoic marine ecosystems that would persist for millions of years.
7. What caused the mass extinction that ended the Ordovician Period?
The end-Ordovician mass extinction, the second-largest in Earth's history, is believed to have been caused by a period of intense global cooling and glaciation. As the supercontinent Gondwana drifted over the South Pole, massive ice sheets formed. This caused two main extinction pulses:
- First Pulse: Sea levels dropped dramatically as water was locked into ice, destroying shallow marine habitats.
- Second Pulse: As the ice age ended, glaciers melted, and sea levels rose rapidly, flooding the newly established habitats with low-oxygen water.
8. Why was the Ordovician Period a critical step for the evolution of vertebrates?
The Ordovician was crucial for vertebrates because it is when the first recognizable members of this group, the agnathans or jawless fish, appeared and began to diversify. These armoured, bottom-dwelling fish were the ancestors of all subsequent vertebrate life, including sharks, bony fish, and eventually, terrestrial animals like amphibians, reptiles, and mammals. Their appearance marked a foundational step before the subsequent "Age of Fishes".
9. What is the geological significance of Ordovician rocks?
Ordovician rocks are geologically significant for several reasons. They are a major source of petroleum and natural gas in some regions, as the abundant organic matter from Ordovician seas was buried and converted into hydrocarbons. These rock layers also contain important index fossils, such as graptolites and conodonts, which geologists use to accurately date and correlate rock strata across different continents.
