Phanerozoic Eon: Paleozoic Era

• Unit 4 covers the Phanerozoic Eon, starting with the Paleozoic Era.

Introduction

• The first 4 billion years of Earth's 4.6 billion-year existence have been reviewed.
• The Hadean, Archean, and Proterozoic Eons were examined.
• Continental masses formed during the Precambrian.
• Plate tectonics formed and broke apart the supercontinents Rodinia and Pannotia.
• Earth experienced two ice ages during the Precambrian.
• Bacteria produced free oxygen and dominated Earth for billions of years.
• Oxygen levels reached 3%-10% at the end of the Precambrian, supporting primitive marine life.
• On an "Earth existence clock", this is 9:00 PM.
• The Precambrian Proterozoic Eon is considered the "beginning life eon".
• The Phanerozoic Eon, marked by visible life, is examined in Unit 4.
• The Paleozoic Era occurred during the Phanerozoic Eon.
• The Paleozoic Era represents approximately 50% of the time since the Precambrian, totaling 291 million years.

Determining the Precambrian-Cambrian Boundary

• The original Cambrian boundary was estimated at 590 MYA, based on the appearance of the first shelly metazoans.
• The current accepted date for the beginning of the Cambrian is about 542 MYA.
• Historically, the Cambrian boundary symbolized the first body fossil of the trilobite Olenellus.
• Testing revealed the original boundary was approximately 525 MYA, necessitating a new selection.
• In 1991, an international committee chose the Chapel Island Formation at Fortune Head, SE Newfoundland, Canada, as the Cambrian-Precambrian boundary.
• The chosen boundary strata corresponds to the first appearance of distinctive trace fossils.
• A fossil boundary in Siberia correlating to the Newfoundland boundary was radiometrically dated at 542 MYA.

Early Paleozoic Era (542 MY – 416 MY)

• The Early Paleozoic Era lasted for 126 million years.
• It is subdivided into the Cambrian, Ordovician, and Silurian Periods.

Late Paleozoic Era (416 MY – 251 MY)

• The Late Paleozoic Era lasted for 165 million years.
• It includes the Devonian, Mississippian, Pennsylvanian, and Permian Periods.
• In Europe, the Carboniferous Period is used instead of the Mississippian and Pennsylvanian Periods.

Paleographic Maps

• One goal of historical geology is to provide paleogeographic reconstructions of early Earth.
• Maps are constructed by synthesizing paleoclimatic, paleomagnetic, paleontologic, sedimentologic, stratigraphic, and tectonic data.

Geography of the Early Paleozoic Era (542 MY – 416 MY)

• North America was one of 5-6 continental landmasses and was named Laurentia.
• Texas was located south of the equator for most of the Early Paleozoic.
• Texas was located north of the equator only during the Late Paleozoic.

Period Maps

• Period maps can be confusing because they are interpretations of geography at a particular time.
• All maps can be plausible for their exact point in time.
• The North American continental outlines are for "reference only."

Paleozoic Sea Levels

• Eustatic sea levels were higher throughout most of the Paleozoic compared to today.
• The Paleozoic Era had long periods without large continental glaciers, contributing to higher sea levels.
• Rapid seafloor spreading and submarine volcanism made the seafloor shallower.
• Extensive continental glaciation occurred twice during the Paleozoic, causing sea levels to drop.
• Sea level changes were most strongly felt over continental landmasses.
• Epicontinental seas were widespread, shallow seas that transgressed or regressed over cratons, especially over Laurentia.
• Transgressive seas describe a rise in sea level, generally over a craton.
• Regressive seas describe a fall in sea level, generally off a craton.
• Rising sea levels leave behind a stratigraphic sequence of sandstone, shales, and limestone.
• This is a transgressive sequence where deep-water sedimentary rocks overlie shallow-water rocks.
• Falling sea levels leave behind a stratigraphic sequence of limestone, shale, and sandstone.
• This forms a regressive sequence, where shallow-water sediments overlie deep-water sediments.
• Walther's Law states that sequential vertical changes in sedimentary rock types equal horizontal sequential changes in rock types and is used to identify transgressions and regressions.

Cambrian Period (542MY – 488 MY)

• Epicontinental seas covered a large portion of the North American craton.
• Transgressive sequences of sediments can be found on each side of the craton.
• There was no life on land during this time
• A series of islands was located to the southwest of the craton.
• The Transcontinental Arch was a series of large, late Cambrian island arcs that extended to southern New Mexico and West Texas.
• Erosion of the craton produced clean sandstone in Wisconsin, like the Cambrian sand in the Bliss Sandstone.
• The Enchanted Rock area in Central Texas had islands because of the Hickory Sandstone.
• Temperatures were warmer during the Cambrian period.
• There were no advancing glaciers and no life on land except bacteria.

Cambrian Big Bang Evolution

• Many different life forms suddenly appeared in the fossil record.
• Simple life forms such as bacteria and algae represent life for billions of years.
• Somewhat complex life forms appeared in the Upper Precambrian Ediacaran Period (630 MY – 542 MY).
• Some evidence suggests that a few Ediacaran life forms survived beyond the Cambrian 542 MY boundary.
• The 542 MY boundary is based on trace fossils and the appearance of "small shelly fauna."
• Early Cambrian fossils found in Yakutia, Siberia in 1993 might predate the first Cambrian trace fossils and were primitive ancestors to sponges, mollusks, and brachiopods.
• The Cambrian Big Bang continued with the sudden appearance of diversified shelly metazoans.
• Complex animals appeared with protective shells for the first time.
• New adaptations included legs, claws, antennas, other appendages, eyes, and mouths with teeth.
• All changes are attributed to adaptive radiation.
• Adaptive radiation involves rapid speciation to fill ecological niches, driven by mutation and natural selection.
• Environmental and genetic changes are likely the cause of adaptive radiation.
• Continued continental breakup allowed for the development of more shallow water habitats.
• Oxygen levels reached a critical level.
• Oxygen levels are needed to aerate tissues and to make structural components like teeth and bone.
• Evolution of predators favored protected prey species.
• Oceanic water chemistry changed to favor the precipitation of calcareous shells.
• Most oceanic iron had been removed and placed into banded iron formations.
• Dolomite supply and deposition decreased, and more dissolved oxygen was present in the water column.
• Widespread submarine volcanism increased the availability of energy and nutrients.
• Mutations drive the process of evolving organisms.
• The best Early Cambrian fossils are found in Chengjiang, China.
• Diverse Early Cambrian fossils were discovered in 1984 in China.
• The fossils are complex, considering that complex life was just beginning on Earth.
• The Cambrian explosion may have occurred in as little as 10 MY.
• Fossils of the same age as those found in China were discovered in Sirius Passet, Greenland, also in 1984.

Burgess Shale Biota

• No discussion of the Cambrian life is complete without discussing the Middle Cambrian Burgess Shale biota in British Columbia, Canada.
• It contains the best examples of soft-bodied flora and fauna from that period.
• The shale offers fossil examples of Earth's first complex animals with shells, heads, mouths, eyes, claws, legs, and other appendages.
• Many animals of the Burgess Shale are "unknown phyla" with no modern organisms with the same basic body plan.
• This biota of invertebrates represents the root stock and basic body parts from all present-day invertebrates and vertebrates.
• Life was more diverse in terms of phyla during the Cambrian than today.
• The biota suggests the Cambrian big bang or explosion occurred over a relatively short period of geologic time.

Life Body Plans

• The pattern for the rest of the history of animal life was set in the Cambrian Period (542 MY – 488 MY).
• Ancestors of all living phyla of shelly invertebrates had appeared by the end of the Cambrian, with no new shelly phyla appearing since.
• Early and Middle Cambrian fossils suggest early experimentation followed by standardization.
• Phylum Chordata includes all bilateral animals related by possessing a notochord.
• A notochord (spinal cord) evolves into a backbone.
• The oldest chordate known is Cathaymyrus diadexus, 535 MY in China.
• The chordate Yunnanozoon has been reassigned to Phylum Hemichordata.
• Pikaia, the next oldest chordate (not vertebrate), found at the Burgess Shale, 520 MY, is a 2-3 inch filter feeder.
• Vertebrates have backbones (covered notochord).
• The oldest known vertebrates are fish.
• Myllokunmingia is one of the oldest known vertebrate fish at 530 MY, found at Chengjiang, China.
• Haikouichths is also found at 530 MY.
• The Cambrian is also known as the Age of the Trilobites.
• All orders of trilobites evolved in the Cambrian.
• Trilobites made up over 50% of the Cambrian fauna (542 MY – 488 MY), with more than 20,000 species that had a wide variety of eye types.
• Trilobites are the world's most popular fossil to collect and rolled themselves up when faced with danger.
• Some trilobites can be found near Llano, Brownwood, and El Paso, Texas.
• Present-day sow bugs and horseshoe crabs are not related to trilobites.
• The end of the Cambrian was marked by colder temperatures and mass extinction of most trilobites.

Ordovician Period (488 MY – 444 MY)

• Ancestral North America was subjected to tectonic forces and colliding landmasses.
• A tectonic collision is called an orogeny, an episode of mountain building associated with convergent zones.
• Intense crustal deformation, metamorphism, igneous intrusions, and thickening of the Earth's crust result from an orogeny.
• This is directly associated with colliding tectonic plates at convergent plate boundaries or subduction zones.

Taconic Orogeny of the Appalachian Mountains (oldest)

• At 510 MYA, the eastern US continental shoreline extended from New York to the Carolinas.
• During the Ordovician, Laurentia remained south of today's equator.
• Before this, the Eastern US shoreline extended only from the Carolinas to New York.
• The Taconic Island Arc headed toward Laurentia during the Early Ordovician.
• The Taconic Island Arc collided first with the Canadian Maritime provinces.
• The arc collision finished by 450 MYA, extending the US coastline from New England to Georgia.
• Igneous intrusions from Georgia to New York have similar age-dating of intrusions, 460 to 440 MYA (Taconic Orogeny).
• Later, two large masses began approaching Laurentia from the eastern coast of the Iapetus Ocean – the continent of Baltica and the Avalonia Islands (Acadian Orogeny).
• The early Appalachian Mountains created by the Taconic Orogeny eroded downwards before the Acadian Orogeny.
• Mountains rise above the surrounding area due to deep roots because Mountains and mountain roots are a property of isostasy.
• Isostasy: Earth's crust floats on a dense underlying layer, where mountains erode and isostatic adjustments push mountain roots upward.
• Isostatic rebound: unloading (erosion) causes the crust to rise until equilibrium is attained.
• Older mountains will always be higher than the surrounding plains and persist over millions of years.
• Ordovician sea levels were very high with transgressive seas over the North American craton until the period's end.
• The Taconic Highlands began to erode.
• Thick sediments were deposited opposite the eastern subduction zone, creating the Queenstown Clastic Wedge.
• In the Early Ordovician, a large deposit of sand-grained filled dolostone (dolomite) was deposited by the seas, called the sandy El Paso Formation in the El Paso area.
• In the Middle Ordovician, large deposits of dolostone (dolomite) were deposited by advancing seas, called the Montoya Formation in the El Paso area.
• East of the El Paso area is the Lower Ordovician Ellenberger Formation, a deep, thick dolomite with 90 large oil fields and 50 major gas fields.
• Outcrops are found near Llano, Texas.
• Cephalopod mollusks grew to more than 18 feet in length.
• Brachiopods increased in importance, and some trilobites survived.
• Plants became well-established in the seas.
• Class Agnatha–Fish of the Ordovician were jawless and became common.
• Some were primitive fish - they lacked a jaw, paired fins, and gut instead of a stomach.
• There were six major groups, including Ostracoderms, a bony-skin fish about 10 inches long that lived only from the Cambrian to the Devonian (542 MY – 416 MY).
• Modern-day examples include lamprey eels and hagfish.
• Primitive algae and lichens invaded the land masses.
• The ending was the third extensive continental glaciation which caused sea levels to drop (regressive seas) and lower water temperature.
• Temperature and sea level drops had a catastrophic effect that led to the mass extinction of many life forms.
• About 12% of Earth's life forms would become extinct.
• Most of the extinctions occurred in shallow tropical waters, including over 100 families of marine invertebrates.
• There were basically no land forms of life yet.

Silurian Period (444 MY – 416 MY)

• Ancestral North America was subjected to tectonics by an approaching land mass.
• Two other large land masses began approaching Laurentia from the western coast of the Iapetus Ocean: the continent of Baltica and the islands of Avalonia.
• Baltica collided with Canada, and Avalonia headed toward the eastern coast of the US.
• But Avalonia did not yet collide with the US.
• The earlier Appalachian Mountains by the Taconic Orogeny began to erode downwards.
• Another period of high sea levels covered most of Laurentia.
• Large reefs blocked seawater in the Michigan basin, resulting in thick salt deposits.
• Large deposits of sandy dolomite (El Paso area) were deposited in Texas, called the Fusselman Dolomite.
• To the east of El Paso, the Fusselman Dolomite is a major oil and gas producer in the deep wells of West Texas.
• Silurian fish took a major evolutionary step forward by developing a jaw.
• Some suggest that the vertebrate jaw began with modifications of the first 2 or 3 gill arches.
• Class Acanthodii were the first fish with jaws (spiny fish) and lived from Silurian to the end of the Paleozoic (444 MY – 251 MY).
• Class Placodermi was a monstrous Silurian armored fish, extinct after only 50 million years.
• Group Arthrodires were giant predators over 20 feet long with giant heads.
• The Silurian saw the development of large sea scorpions up to three feet long.
• Later, sea scorpions evolved up to 10 feet long.
• Even with the transgressive seas, some land was available for life to invade and a food supply for the animals.
• The first invasion of living organisms would take place with algae and vascular plants.
• This occurred about 430 MY ago.
• The earliest known vascular plant is Psilopsids.
• The earliest animals on land were insects.
• The oldest known fossil insect is the millipede (Silurian Age) and bizarre giant, scorpion-like insects that invaded the shorelines.
• The Silurian Period is often called the Age of the Corals because of the great abundance.
• The end of the Silurian Period is marked by the extinction of a few groups of small marine creatures.

Devonian Period (416 MT – 359 MY)

• Life and Earth underwent some major changes.

• The Acadian Orogeny had plates of Laurentia, Baltica and Avalonia converging.

• The early Appalachian Mountains created by the Taconic Orogeny had eroded.

• Baltica had converged with Canada, and Avalonia was converging toward the eastern US coast.

• The final convergence of the Acadian Orogeny created the Appalachian Mountains.

• Euramerica consists of landmasses created by the Taconic, Acadian and Antler Orogenies.

• Euramerica (or Laurasia) formed.

• There were mostly transgressive seas during the Devonian with some times of regression, a thin layer of Devonian rocks found in Texas, the Canutillo Limestone in the El Paso area.

• Reefs blocked seawater from the Williston Basin in Canada, creating salt and potash deposits.

• Land plants became widespread, large, and diversified, including tall trees (seed-bearing gymnosperms) by the end

• Earth becomes slightly more familiar.

• There were still some trilobite species in the shallow Devonian Sea.

• Major changes were occurring in the shallow Devonian Sea, especially with fish and is also known as the Age of Fish.

• All five classes of fish were alive and no new classes formed.

• Class Chondrichthyes includes cartilaginous fish, as well as extinct sharks including: Cladoselache, Heliocoprion, Stethacanthus and Farukatasu

• Class Osteichthyes (bony fish) includes the lobe-finned Coelacanth that first appeared and rediscovered as a living fish in 1938.

• They have articulated bones within stubby fins and muscles.

• Beginning of tetrapod limbs.

• Tetrapod: Vertebrate animals having four feet or leg-like appendages (excludes fish) with the lungfish with the Order Dipnoi as the first seen in the Devonian.

• Lungfish have external nostrils, lungs, and gills with bones in fins with muscles, including the Devonian Panderichthys.

• Acanthostega was thought to be and amphibian with no lungs

• Mudskippers are modern tetrapod fish.

• It is suspected that Eusthenopteron fed out of the water along the shoreline.

• An air-breathing fish with front legs, Tiktaalik roseae, has been hailed as the missing link to amphibians.

• Large +365 MY animals were walking in shallow water from discovered footprints.

• The first tetrapod ancestors of amphibians are found calling Ichthyostega the labyrinthodonts had seven toes on its back fins (feet).

• At the end of the Devonian, a mass extinction affected about 14% of Earth's life forms and collapsed massive reef communities and one class of fish.

• Warm water environments were affected, not cool water environments where primitive land plants and the Devonian mass extinction may have taken a few million years to complete

Mississippian Period (359 MY – 318 MY)

• Earth is preparing for its largest collision where at 327 MY Euramerica (Laurasia) is headed toward Gondwana which will produce Pangaea.

• Convergence sutures the masses together and tectonics create the third generation of the Appalachian Mountains when Africa converges.

• The Mississippi Period is the last very widespread transgressive epicontinental sea with vast shale deposits in many parts of North America, including the Barnett Formation of Central and West Texas.

• Widespread oil and gas wells using horizontal drilling and fracking contribute over $100 Billion to the Texas economy.

• Epicontinental seas contain abundant forms of life.

• Although the Mississippian Period is the Carboniferous Period", there is very little is in the U.S.

• The Mississippian is also called the Age of the Crinoids (sea lilies), Blastoids became very common.

• Amphibians were walking with 350 footprints found in Canada but had to lay gelatinous eggs in water.

• The next step of vertebrates to be the development of the amniotic egg of the parents (reptiles) will provide a greater opportunity.

• A small lizard-like Westlothiana (350 MY) is the first reptile found in Scotland but the eal Age of the Reptiles" is the Permian Period, where Reptile would take less than 60 MY .

• At the end of the Mississippian Period, CO2 levels dropped and the world temperatures dropped .

• The Mississippian Period would end with the minor extinction of a few sea creatures.

Pennsylvania Period (318 MY – 299 MY)

• The "big collision" will begin with the Allegheny Orogeny where The latest Appalachian Mountains are part of supercontinent Pangaea will be until Permian times before the convergence with Africa will end.
• South America converges with North America forming the Ouachita Mountains, lifting Llano in central Texas, having fewer epicontinental seas that exposed a western islands in the US.
• Pengaea near complete, major coal deposits will form in the eastern U.S and Texas and evaporation causes thick salt as well as potash deposits occurs in New Mexico and Utah.
• Outcrops of Pennsylvanian limestone can be found in north-central Texas and Craton is part of Pangaea having present Appalachians, Ouachita and Antler Mountains.
• Swamps create coal deposits where seas collect in the basins as well as large deposits of potash created in New Mexico and Utah.
• Near the equator a reptile arrives that is lizard-like Hylonomus has been found in the 300 MY (Pennsylvanian) Joggins Formation, Nova Scotia in Canada along with the first mammal-like as this Period Age of Plants and insects.
• Winged insects who had developed wings in the Devonian Period is now common as dragonflies become giants and more than a thousand species called the Age of the Cockroaches"

Permian Period (299 MY – 251 MT)

• The Allegheny Orogeny completed the supercontinent of Pengaea and the the Appalachian - Caledonian are made where Earth survives it's fourth ice age.

• There are common glaciers and desserts, fewer transgressive and shallow seas.

• Castile Gypsum has a large evaporate basin in West Texas where the Texan Permain Bassons are inland seas from the west with world's famous Permian reef El Capitan while the Utah area's Phosphoric Sea has fertiliser phosphates.

• Animal life expanded on the lands where primitive amphibians lived along the Texan Shore

• The Permian Period is also known as the Age of the Mammal-like" reptiles and the end -with fail.

• Finned-back Pelycosaurs are mammal-like reptiles including the Dimetrodon and herbivore Edaphosaurus in Archer County. Mamal Like Includes

  • primitive dentition
  • and are several skeleton characteristics where no true mammals have been found and end up creating deserts.

The Permian Period had the largest mass extinction recorded.

Extinctions

• 90% -95% of all marine invertebrate species died out

• There was only one out of many Crinoids species"

• all of the

• Blastoids

• Brachiopods

• Gastropods

• Order of insects

• Two Orders of coral

• 75% All reptiles

• 67% All amphibians

• Class of fish

• Trilobites has disappeared Timing

• The extinction of Perrmian took occurred in a period less than 800,000 in the era of the extinction, the Mesozoic life form after a low diversity species has become abundant.

Probable cause of Permian mass extinction

• Not Certain"
• Exctinction is the ultimate fate of all species" This can cause severe mass extinction.

Types of Extinctions

• Background (continued extinction)
• Mass extinction (twice the background rate)
• Minor is as same like the decreased I the end

This can occurs after a few million years after signfican environment and for one species their death is benificial for others to be dominant.

Tectonics

• creates Climate and a super continant"

Other

• such as magnetic reverses but never has there been a extinction during the phanerozoic Eon"