University of Liberia

1. University of Liberia GEOL. 303: PALEONTOLOGY AND STRATIGRAPHY PRESENTATION THE EVOLUTION OF THE BIOSHERE WITH RESPECT TO THE ORDOVICIAN PERIOD

2. AUTHOR: Sam O.Grose CO- AUTHOR: Janneh V. Dukuly

3. INTRODUCTION • This Research is focus on the evolution of the Biosphere during the Ordovician Period. It takes into account brief history of the origin of the name Ordovician, tectonic activities, and paleoclamatic conditions, paleogeography. It also include study on sea level, marine organisms, invertebrates, stratigraphy, terrestrial organism, Ordovician radiation,( Its causes) and mass extinction that occur at the end of the period.

4. EXECUTIVE SUMMARY • The Ordovician Period is best known by its intense diversification (an increase in the number of species) of marine animal life in what became known as the Ordovician radiation. This event precipitated the appearance of almost every modern phylum (a group of organisms having the same body plan) of marine invertebrate by the end of the period, as well as the rise of fish. Ordovician seas were filled with a diverse assemblage of invertebrates, dominated by brachiopods (lamp shells), bryozoans (moss animals), trilobites, mollusks, echinoderms (a group of spiny-skinned marine invertebrates), and graptolites (small, colonial, planktonic animals), A typical marine community consisted of these animals, plus red and green algae. On land the first plants appeared, as well as possibly the first invasion of terrestrial arthropods. The end of the Ordovician was heralded by a mass extinction, the second largest in Earth’s history. (The largest mass extinction took place at the end of the Permian Period and resulted in the loss of about 90 percent of existing species.

5. EVOLUTION OF THE BIOSPHERE (ORDOVICIAN PERIOD) /BRIEF HISTORY • The Ordovician was named by the English geologist Charles Lapworth in 1879 to define the disputed overlapping interval over the boundaries of the Cambrian and Silurian systems. He took the name from an ancient Celtic tribe, the Ordovices, renowned for its resistance to Roman domination. It is the second of the six periods in the Paleozoic era of the Phanerozoic eon. The Ordovician was demarcated in the late 19th century as a compromise in a dispute over the boundaries of the Cambrian and Silurian systems. • The Ordovician Period lasted almost 45 million years, beginning 488.3 million years ago and ending 443.7 million years ago. It is divided into three epochs: Early Ordovician (485.4 million to 470 million years ago), Middle Ordovician (470 million to 458.4 million years. The Ordovician Period is best known by its intense diversification (an increase in the number of species) of marine animal life in what became known as the Ordovician radiation. ago), and Late Ordovician (458.4 million to 443.8 million years ago).

6. PALEOCLIMATE and tectonics • Numerical climate models as well as carbonisotope measurements from preserved Ordovician soils suggest that atmospheric levels carbon dioxide during the period were 14–16 times higher than today. These high levels were driven by widespread volcanic activity, which released large volumes of carbon dioxide into the atmosphere. High sea levels flooding of continents, and the lack of widespread vegetation on land, had suppressed weatheringof silicate rocks, a major mechanism for removing carbon dioxide from the atmosphere. In short, therefore the addition of carbon dioxide to the atmosphere increased during the Ordovician Period. • Map of the atmosphere and climates during the Ordovician High sea level supressedthe weathering of silicates

7. tectonics • All of the major tectonic plates were in motion during the Ordovician Period. The first major rifting events that resulted in the division of Rodinia into pieces occurred as early as 750 million years ago. Following the breakup of the supercontinent, extensive oceanic ridges were established, circling the globe and creating the Paleotethys Sea and Iapetus and Panthalassic oceans. Ordovician volcanism was extensive and was primarily generated at subduction zones and oceanic ridges. Production of oceanic lithosphere at these ridges was accommodated through its destruction at subduction zones. The Panthalassic Ocean was bordered on all sides by subduction zones, much like the Pacific Ocean is today. A subduction zone also separated Laurentia from both Siberia and Baltica. • Map of Tectonics activities during the Ordovician

8. paleogeography • During the Ordovician Period, four major continents were present and separated by three major oceans. Although the continents positions are updated with new evidence, current understanding of their position is based on paleomagnetic evidence, fossil markers, and climatically sensitive sediments, such as evaporite minerals. The craton (stable interior portion of a continent) of Laurentia made up of most of present-day North America, Greenland, and part of Scotland straddled the Equator and was rotated approximately 45° clockwise from its present orientation. • earth during the Ordovician period

9. The craton ( paleogeography cont.) • The craton made up of Siberian and Kazakhstania (Siberia-Kazakhstan) lay east of Laurentia, along and slightly north of the Equator. The Iapetus Ocean separated these two landmasses on the south from the Balticacraton, ( Scandinavia and north-central Europe). The micro continent of Avalonia ( England, New England, and maritime Canada )was positioned to the west of Baltica and also faced Laurentia across the Iapetus Ocean. The Paleotethys Sea separated Avalonia, Baltica, and Kazakhstan from the supercontinent of Gondwana. This immense supercontinent straddled both the South Pole, ( northwest Africa), and the Equator, which then crossed present-day Australia and Antarctica. In this position, Africa and South America were rotated nearly 180° from their present orientation. A single body of water, the Panthalassic Ocean, covered almost the entire Northern Hemisphere and was as wide at the Equator as the modern Pacific Ocean. • North America's Craton

10. SEA level • The rate of seafloor spreading that followed the breakup of the supercontinent Rodinia near the end of the Proterozoic Eon (2.5 billion to 541 million years ago) peaked during the Ordovician Period. Tall oceanic ridges produced by this activity raised the average elevation of the seafloor and flooded parts of many continents, creating vast shallow seas within their interiors and at their margins. During the Early and Late Ordovician epochs, almost all of North America was submerged under these epicontinental seas.

11. Sea level(cont.) • Sea level fluctuated continuously throughout the Ordovician. Sea level was highest during the Early and Late Ordovician epochs and it was up to 200 meters (about 660 feet) lower during the Middle Ordovician Epoch. Numerous shorter-term fluctuations were superimposed on this broad rise and fall, with each fluctuation typically lasting one to five million years. Additional minor fluctuations of a few metres or less, occurring on the order of tens to hundreds of thousands of years, have also been identified. The causes of these changes in sea level are difficult to identify. Some may have been driven by variations in the rates of plate motion, some by glaciations, some by local tectonic uplift or subsidence, and some by changes in groundwater storage capacity. The end of the Ordovician Period is marked by a pronounced fall in sea level of nearly 160 meters (525 feet), which was triggered by the rapid expansion of continental ice sheets on Gondwana.

12. Ordovician life • Ordovician seas were characterized by a rich and diverse assemblage of species. Calcified microbial mats, known as stromatolites, are found in Ordovician rocks, although they are not as common there as in strata from the Proterozoic Eon and Cambrian Period (2.5 billion to 485.4 million years ago). Chitinozoans or acritarchs, microfossils with a hollow cavity and organic walls, represent the phytoplankton (small, free-floating, photosynthetic organisms) Living stromatolites in Hamelin Pool of Shark Bay, Western Australia.

13. Invertebrates( Ordovician life cont.) • Invertebrate life became increasingly diverse and complex through the Ordovician. Both calcareous and siliceous sponges are known; among other types, the stromatoporoids first appeared in the Ordovician. Tabulata (platform) and rugosa corals (horn corals) also first appeared in the Ordovician, the solitary or horn corals being especially distinctive. Bryozoans (moss animals) and brachiopods (lamp shells) were a dominant component of many assemblages. Mollusks were also common and included the gastropods, monoplacophorans (limpet-shaped, segmented mollusks), bivalves, cephalopods, chitins, scaphopods (tusk shells), and rostroconchs (single-shelled mollusks) • Streptelasma, an extinct genus of coral from the Ordovician Period

14. Stratigraphy • For decades, the epochs and series of the Ordovician each had a type location in Britain, where their characteristic faunas could be found, but in recent years, the Stratigraphy of the Ordovician has been completely reworked. Graptolites, extinct planktonic organisms, have been and still are used to correlate Ordovician strata. Particularly good examples of Ordovician sequences are found in China (Yangtze Gorge area, Hubei Province), Western Australia (Emanuel Formation, Canning Basin), Argentina (La Chilca Formation, San Juan Province), the United States (Bear River Range, Utah), and Canada (Survey Peak Formation, Alberta). Ordovician rocks over much of these areas are typified by a considerable thickness of lime and other carbonate rocks that accumulated in shallow subtidal and intertidal environments. Quartzites are also present. Rocks formed from sediments deposited on the margins of Ordovician shelves are commonly dark, organic-rich mudstones which bear the remains of graptolites and may have thin seams of iron sulfide. Unique mineralogical and geochemical features of many Ordovician volcanic ashes allow them to be correlated over long distances.

15. extinction • Mass extinction at the end of the Ordovician: The Ordovician Period was terminated by an interval of mass extinction. This extinction interval ranks second in severity to the one that occurred at the boundary between the Permian and Triassic periods in terms of the percentage of marine families affected, and it was almost twice as severe as the extinction event that occurred at the end of the Cretaceous Period, which is famous for bringing an end to the dinosaurs. An estimated 85 percent of all Ordovician species became extinct during the end-Ordovician extinction in the nearly two-million-year-long Hirnantian Age and the subsequent Rhuddanian Age of the Silurian Period.

16. conclusion • The Ordovician marks the beginning of the entire marine community, it was also a time of mass extinctions in the marine realm. More than 100 families of marine invertebrates became extinct, and in North America alone, about half of the brachiopods and bryozoans died out. What caused such an event? Many geologists think these extinctions were the result of extensive glaciation in Gondwana at the end of the Ordovician Period. However, when Gondwana finally settled on the South Pole during the Upper Ordovician, massive glaciers formed, causing shallow seas to drain and sea levels to drop. This likely caused the mass extinctions that characterize the end of the Ordovician in which 60% of all marine invertebrate general and 25% of all families went extinct.

17. Q & A