VIZUALIZING EARTH HISTORY

1. VIZUALIZING EARTH HISTORY By Loren E. Babcock Chapter 10 Paleozoic World

2. Early Paleozoic Cambrian overview At the start of the Paleozoic Era, Earth’s tectonic plates were in a transitional stage between the breakup of Pannotia and reassembly as Pangea. Major cratonic pieces were Laurentia, Baltica, Siberia, and Gondwana. Epeiric sea - Shallow sea formed when marine water covers part of the continental crust. Also called epicontinental sea. Global sea level was relatively high through most of the Paleozoic Era. As a result, thick successions of marine sediments were deposited on continental shelves.

3. Early Paleozoic Cambrian overview

4. Early Paleozoic The Ediacaran-Cambrian transition. Evolution’s Big Bang The early evolutionary radiation of multicellular organisms is commonly called the “Cambrian explosion.” Not only did numerous organisms emerge during this time, but a variety of animals evolved resistant coverings or skeletons that could be preserved as fossils. Cambrian explosion - The appearance of numerous taxonomic groups in the Cambrian. It reflects a widespread evolutionary diversification especially among multicellular animals.

5. Early Paleozoic Evolution’s Big Bang/Major life forms of the Cambrian Trilobite - A Paleozoic marine arthropod characterized by a calcified exoskeleton divided lengthwise into three lobes. Cephalopods - Swimming carnivorous mollusks, which had shelly skeletons, first appeared in the fossil record. Conodont - An extinct early chordate that secreted phosphatic tooth-like structures along the pharynx. Chordate - An animal possessing a notochord and pharyngeal gill slits. Graptolite - An extinct hemichordate animal, or chordate relative, that had an organic skeleton.

6. Early Paleozoic Exceptional preservation of fossils and Cambrian biodiversity A large and important share of the preserved record of Cambrian biodiversity came from organisms lacking biomineralized skeletons. Coinciding with the first appearance of trilobites are some of the earliest Phanerozoic deposits containing exceptionally preserved fossils. Cambrian strata include an unusually large number of such deposits, like the the Burgess Shale of British Columbia, Canada, and the Chengjiang deposit of Yunnan, China.

7. Early Paleozoic Exceptional preservation of fossils and Cambrian biodiversity

8. Early Paleozoic Explain how exceptional preservation of fossils has increased our understanding of ancient life. Most Cambrian organisms had non-biomineralized external coverings. Most animals had exoskeletons made of chitin. Although chitin affords some protection, it is made of sugar and makes a good meal for many predators. Other non-biomineralizing life forms —the organisms without hard parts— comprised 90% or more of the fossils in some Cambrian deposits. This implies that where only hard part-bearing fossils are preserved, most of the original biodiversity has been filtered out of the fossil record.

9. Early Paleozoic Cambrian Predatory-prey System

10. Early Paleozoic Ordovician sea level and tectonics During the Ordovician, global sea levels reached some of the highest positions ever. The sea level rise of the Ediacaran-Cambrian continued into the earliest Ordovician, but before the end of the Early Ordovician it dropped precipitously. Shifting plates delivered big changes to the Ordovician world. Closure of the Iapetus Ocean closed the distance between Laurentia and Avalonia, and brought tectonism to eastern Laurentia and environs. Iapetus - The proto-Atlantic Ocean.

11. Early Paleozoic Paleozoic tectonic events. Orogenesis, or mountain building, on the Laurentian mainland resulted in the rise of the Taconic Mountains. This event, the Taconic orogeny, was the first of three mountain building episodes along the Appalachian margin of Laurentia during the Paleozoic. Plate collision caused the thrusting of large wedges of flysch over shallow carbonate deposits. In places, slices of basaltic ocean floor, or ophiolites, were thrusted onto the craton as well. Closure of Iapetus caused the collision of island volcanoes and other crustal pieces, including Avalonia, with eastern Laurentia.

12. Early Paleozoic Ordovician marine life The Ordovician Period marks the appearance of an assemblage of marine life characteristic of the post-Cambrian Paleozoic. Extinctions in the late part of the Cambrian took a toll on animal groups, but the recovery was unexceptional. Trilobites, mollusks, and brachiopods diversified at a fairly slow rate. Few niche spaces were newly reopened to be exploited. Cephalopods became the top predators in marine environments around the beginning of the Ordovician.

13. Early Paleozoic Ordovician marine life

14. Early Paleozoic Ordovician marine life Fishes were a threat to marine life of the Cambrian and Ordovician, although the extent of their impact is hard to assess. Graptolites, stalked crinoids (or sea lilies), bryozoan colonies, and mollusks made some evolutionary gains in the Ordovician but they were setting the groundwork for more spectacular developments later. By the end of the Ordovician, cyanobacterial mounds were a rarity in normal marine environments.

15. Early Paleozoic Early forays onto the land Live organisms were washed ashore early in Earth’s history. Trace fossils from beach sandstones suggest that animals occasionally crawled on dry land as early as the Cambrian. They may have left the water by accident or even deliberately — perhaps the shore was a place to bury eggs. The first evidence of plants conquering the land comes from the Cambrian. These early land plants were probably from a marine sister group, the green algae. Spores are the only known evidence of terrestrial plants older than the Silurian, when stems of land plants became fossilized.

16. Early Paleozoic Ordovician glaciation and extinction At the end of the Ordovician, global temperatures dropped and the ice cap in southern Gondwana expanded. In Gondwana, tillites, dropstones, and striated pavements record the glacial event. The effect of climate change on the biosphere was quick and catastrophic: it precipitated one of the most severe mass extinctions in Earth history. As glaciation reached a maximum, brachiopods, bryozoans, corals, trilobites, conodonts, and nautiloids disappeared in large numbers.

17. Middle Paleozoic Silurian-Devonian tectonics and sea level By the early part of the Silurian Period, Taconic mountain building had ceased in eastern Laurentia, and erosion left few remnants of the mountains. In the mid-Silurian, renewed subduction and closure of Iapetus caused Baltica to collide with Laurentia, principally along what is now eastern Greenland and Norway-Scotland-Ireland.

18. Middle Paleozoic

19. Middle Paleozoic Silurian-Devonian tectonics and sea level Euramerica - A composite continent formed by collision of Laurentia with Avalonia and Baltica during the Devonian Period. Caledonian orogeny - Silurian-Devonian orogenic activity that affected western Europe from the British Isles through Scandinavia. Acadian orogeny - Orogenic activity during the Devonian along the Appalachian margin of Laurentia.

20. Middle Paleozoic Explain the tectonosedimentary cycle. Tectonosedimentary cycle - The record of continental collision in basinal sedimentation patterns. It comprises passive margin sedimentation followed by deep water (foreland basin) deposits and then shallow water to nonmarine deltaic deposits. Rivers carried detrital sediments eroded from the Acadian Mountains to their mouths along the shoreline of the Appalachian Basin, then deposited their loads in an ever-thickening clastic wedge called the Catskill Delta.

21. Middle Paleozoic Mid-Paleozoic marine life Glaciation at the end of the Ordovician decimated many shallow marine invertebrates, but recovery came rather soon as marine water flooded shelf areas, opening new habitats. Trilobites were still important in marine ecosystems, but they never were as diverse after the Ordovician extinction as they were before it. Corals, especially the massive, fast-growing tabulate corals, and coralline sponges, both refilled vacant niches and diversified into unfilled niche space.

22. Middle Paleozoic Mid-Paleozoic marine life Graptolites, almost disappeared at the end of the Ordovician, increased their numbers greatly during the Silurian Period. During the Silurian, marine life underwent ecological reorganization, a new ecological “arms race” between predators and prey ensued. The most notable evolutionary event of the mid-Paleozoic was the rise of jawed fishes. Jaws made it possible for fishes to bite into prey, and even to crush shells or skeletons. The Devonian is called the “Age of Fishes.”

23. Middle Paleozoic The invasion of land by plants and animals. Plants and animals appeared on land in several phases during the Paleozoic. A complete transition to land occurred by the end of the Silurian, and adaptation was completed in the Devonian Period. Life on land has certain basic requirements that are different from the requirements for life in water. The primary problems associated with the transition to land are: 1. gas exchange with the outside environment; 2. internal fluid flow and maintaining osmotic balance; 3. maintaining support for the body; 4. internal temperature regulation and prevention of desiccation; and 5. protection of developing embryos.

24. Middle Paleozoic The invasion of land by plants and animals Insect - An arthropod having three pairs of legs and wings, at least primitively. The evolution of winged insects from non-wing-bearing Terrestrial hexapods around the Middle Devonian marks the beginning of evolution’s greatest animal success story. By the end of the Carboniferous Period, insects had undergone an almost unimaginably large adaptive radiation, and a high reproductive rate leading to rapid speciation.

25. Middle Paleozoic Devonian glaciation and biotic crisis Late in the Devonian the polar ice cap in Gondwana expanded during a time when Earth was entering a cooling phase. At the same time, marine organisms declined in species diversity. More than 50% of genera known from fossils disappeared in a time span of perhaps 3 million years. Brachiopods, trilobites, conodonts, ammonoids, and jawless fishes all suffered major losses in the Late Devonian.

26. Late Paleozoic Carboniferous-Permian tectonic, climate, and sea level The late Paleozoic was a time of important tectonic change, and tectonic events influenced global climatic and sea level changes. Each of the mountain building events (the Taconic orogeny in the Ordovician Period, the Acadian orogeny in the Devonian Period, and the Alleghanian orogeny in the Carboniferous and Permian periods) was followed by the opening of an ocean basin. The cyclic recurrence of plate-tectonic spreading and basin closure through subduction has been referred to as a Wilson cycle.

27. Late Paleozoic Carboniferous glacial-interglacial cycles Climatic conditions of the Carboniferous were a study in contrasts. A greenhouse world in the early half of the period (the Mississippian) gave way to a series of rapid glacial cycles, reflected in sea level fluctuations, in the later half (the Pennsylvanian). Milankovitch cycles - Longer intervals (41,000-year cycles) resulted from the tilt of the Earth’s axis, which affects where and how much sunlight falls on the globe. The longest cycles, 100,000 to 120,000 years, are related to the deviation over time in the Earth’s elliptical orbit around the Sun. Less of the Sun’s energy arrives on Earth when the Earth is at a distant point in its orbital path than when it is closer to the Sun.

28. Late Paleozoic Carboniferous glacial-interglacial cycles and their effects on sedimentation patterns globally. Cyclothems show a change upsection from continental deposits including redbeds, fluvial sediments and coal beds, through marginal-marine and shallow marine sandstones, siltstones, and limestones, to deeper water gray and black shales. The shales mark an inflection point as sea level was shifting from a transgressive (deepening) phase to a regressive (shallowing) phase.

30. Late Peleozoic marine life Marine life of the Carboniferous was similar to that of the Devonian. The seas were rich in brachiopods, bryozoans, and mollusks. Trilobites were no longer diverse, but some species were locally abundant. In the Carboniferous (Mississippian) deposits of crinoid-rich limestones or encrinites were abundant. Crinoids and other stalked echinoderms formed impressive “meadows” stretching for hundreds of kilometers across the warm, shallow, epeiric seas.

31. Late Paleozoic terrestrial life The most conspicuous terrestrial life forms of the Carboniferous and Permian were plants. During warmer intervals, especially in the late part of the Carboniferous, forests flourished in extensive coastal wetlands of the tropics. These areas of massive vegetative production are sometimes referred to as “coal swamps.” The world’s coal reserves come from thick peat deposits, which were lithified to coal seams, deposited in these settings. It was the prominent coal beds of Britain that gave rise to the name “Carboniferous.”

33. Late Paleozoic Understand the major marine and terrestrial life forms of the Carboniferous-Permian. Reptiles appeared in the late Carboniferous, and in the Permian, they began diversifying into the groups we know as squamates (lizards and snakes), archosaurs (crocodiles, dinosaurs, and flying reptiles), and others. Big evolutionary advantages they had over their amphibian ancestors were internal fertilization and an amniotic egg. The synapsids first appeared in the late Carboniferous and diversified in the Permian. Synapsids have only one jaw bone in each side of the lower jaw.

34. Late Paleozoic Permian extinction More than 80% of all marine species became extinct in the waning stages of the Permian Period. The causes of the Permian biotic crisis were a combination of changes that dealt the lethal blow to so many species. The fusing of the continents into the supercontinent Pangea, reduced the area of shallow epeiric seas. Adding to the crisis, sea level dropped roughly 100 meters during the last 2 million years of the Permian Period. Large continental fissure eruptions in Siberia and China may have blocked sunlight from reaching the Earth or added CO2 and water vapor to the atmosphere, enhancing the greenhouse effect.