Welcome To My Website

• Home
• About Me
• Gallery
• Links/Map
• Contact

---

The Ordovician Period: (505 million years ago)

 

In geologic time , the Ordovician Period, the second period of the Paleozoic Era , covers the time roughly 505 million years ago (mya) until 438 mya. The name Ordovician derives from that of the Ordovices, an ancient British tribe.

 

Much of the continental crust that exists now had already been formed by the time of the Ordovician Period and the forces driving plate tectonics actively shaped the fusing continental landmasses. Near the margins of the continental landmasses, extensive mountain building allowed the development of mountain chains . Almost all life during this period lived in the ocean. The only land life was in the form of very primitive plants very near the water line of the coasts, probably mosses and algae and were of a non-vascular nature. Insects did not yet exist, nor did amphibians or reptiles. Fish as we know them did not exist, although a form of primitive fish began to appear by the end of the Ordovician. Though Ordovician life sounds primitive by today's standards, the life during this period was more advanced than life in the earlier Cambrian Period. Ordovician life was characterized by a dramatic increase of the shelly fauna, corals, and bryozoans.

 

By the end of the Ordovician Period, primitive jawless fish called Ostracoderms appeared. These primitive fish were covered with bony plates and were among the first vertebrates on the earth. The Earth during the Ordovician period looked very different from the Earth that we know today. This is the result of Plate Techtonics.

 

The fossil record establishes that vertebrates existed during the Ordovician Period. As with the Cambrian Period, the Ordovician Period ended with a mass extinction of nearly a third of all species. This mass extinction, approximately 438 mya, marked the end of the Ordovician Period and the start of the Silurian Period .

 

Although there is no evidence of an occurrence equivalent to the K-T Event, it is possible that an impact from a large meteorite may have been responsible for the mass extinction marking the end of the Cambrian Period and start of the Ordovician Period. Impact craters dating to the Ordovician Period have been identified in Australia .

The End of the Ordovician Period

The Ordovician Period came to a close in a series of extinction events that, taken together, comprise the second largest of the five major extinction events in Earth's history in terms of percentage of genera that went extinct. The most commonly accepted theory is that these events were triggered by the onset of most cold conditions in the late Katian, followed by an ice age, in the Hirnantian faunal stage, that ended the long, stable greenhouse conditions typical of the Ordovician.

 

The ice age was possibly not long-lasting, study of oxygen isotopes in fossil brachiopods showing that its duration could have been only 0.5 to 1.5 million years. Other researchers (Page et al.) estimate more temperate conditions did not return until the late Silurian. Surviving species were those that coped with the changed conditions and filled the ecological niches left by the extinctions.

 

At the end of the second event, melting glaciers caused the sea level to rise and stabilise once more. The rebound of life's diversity with the permanent re-flooding of continental shelves at the onset of the Silurian saw increased biodiversity within the surviving Orders.

 

Map of the Earth during the Ordovician Period

 

 

 

 

 

 

Paleozoic Era

Mesozoic Era