(Revised 7/11)
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- We have reviewed the first 4 BY (Precambrian) of our Earth’s 4.56 BY of existence
- We examined the Earth for the Hadean Eon, the Archean Eon, and the Proterozoic Eon.
- During the Precambrian, we saw continental masses being created
- Then plate tectonics really “kicked in” to create and tear apart two supercontinents - Rodinia and
- Earth had two ice ages during this period
- Bacteria ruled the Earth for billions of years and they created the free oxygen for our atmosphere
- At the end of the Precambrian, we saw oxygen levels reach 3% - 10% and a few primitive life forms
in the shallow seas
- On a 24 hour “Earth existence clock”, it is now 9:00 PM
- The Precambrian Proterozoic Eon was the beginning life eon”
- We now enter the last eon – The Phanerozoic (visible life) Eon
- With this unit we will examine the Paleozoic (early life) Era of the Phanerozoic Eon
- The Paleozoic (early life) Era of the Phanerozoic (visible life) Eon represents almost 50% of the time
since the Precambrian (a total of 291 MY).
Determining the Precambrian-Cambrian Boundary
- Original boundary was based on what was thought to be the appearance of the first shelly metazoans.
- Date for the beginning of the Cambrian was originally estimated at 590 MY.
- Today’s date for the beginning of the Cambrian is about 542 MY.
- Traditionally the Cambrian boundary was picked to represent the appearance of the first body fossil
of the trilobite Olenellus
- Testing found the original boundary was actually at 525 MY, not 590 MY, so a new boundary had to
- In 1991, an international committee selected the Chapel Island Formation at Fountain Head, SE
Newfoundland Canada to represent the Cambrian-Precambrian boundary.
- This boundary strata (chosen in 1991) corresponds to the first appearance of distinctive trace fossils
and not body fossils. A fossil boundary in Siberia that correlated to the Newfoundland boundary was
radiometrically age dated at 542 MY.
Early Paleozoic Era (542 MY – 416 MY)
- The Early Paleozoic Era lasted for 126 MY.
- It is subdivided into the Cambrian Period, Ordovician Period, and Silurian Period.
Late Paleozoic Era (416 MY – 251 MY)
- The Late Paleozoic Era lasted for 165 MY.
- It includes the Devonian Period, Mississippian Period, Pennsylvanian Period and the Permian Period.
- In Europe they use the Carboniferous Period instead of the Mississippian and Pennsylvanian Periods.
Paleographic Maps
- One of the goals of historical geology is to provide paleographic reconstructions of early Earth.
- The maps can be constructed by synthesizing all of the pertinent paleoclimatic, paleomagnetic,
paleontologic, sedimentologic, stratigraphic and tectonic data available.
Geography of the Early Paleozoic Era (542 MY – 416 MY)
- North America was one of the 5-6 continental land masses at that time.
- Ancestral North America is named Laurentia.
- For most of the Early Paleozoic, Texas would have been found south of the equator.
- Only during the Late Paleozoic would Texas again be north of the equator.
Period Maps
- Period maps can sometimes be confusing (used as an example maps of the Cambrian)
- The maps are interpretations of the geography of an area for a particular time in the geologic past.
- All of these maps can be plausible for their exact point in time
- The North American continental outlines shown on these maps won’t exist for millions of years
- The US and North American outlines are for “reference only” on all the maps
Paleozoic Sea Levels
- Eustatic (world-wide) sea levels were higher throughout most of the Paleozoic than the levels of
- The Paleozoic Era had long periods of no large continental glaciers which would equal to a higher sea
- Rapid sea floor spreading and submarine volcanism can make a significant portion of the sea floor
- Twice during the Paleozoic, there would be extensive continental glaciation which would cause sea
levels to drop.
- Sea level changes would be most strongly felt over continental land masses.
- (Returned to a Cambrian Period map as an example)
- Epicontinental (Epeiric) sea: widespread, shallow seas that transgress or regress over a craton.
- This was a common feature of the various periods of the Paleozoic Era, especially over Laurentia
(North America).
- Transgressive: describes a rise in sea level, generally over a craton (left map).
- Regressive: describes a fall in sea level, generally off a craton (right map).
Transgressive Seas (Using a Cambrian Period map as an example)
- Transgressive: describes a rise in sea level, generally over a craton, this would leave behind a
stratigraphic sequence.
- This situation (rocks) can provide a record of the rising sea level: sandstone overlain by shales
overlain by limestone.
- Transgressive sequence: deep-water, sedimentary-rock sequence that overlies shallow-water,
sedimentary-rock sequence.
Regressive Seas
- Regressive: describes a fall in sea level, generally off a craton; this would leave behind a stratigraphic
- This situation (rocks) can provide a record of falling sea level: limestone overlain by shale overlain
by sandstone.
- Regressive sequence: shallow-water sedimentary-rock sequence that overlies deep-water,
sedimentary-rock sequences.
FYI: Walther’s Law: can be used to identify transgressions and regressions.
- This law states that the sequential vertical changes in sedimentary rock types will equal horizontal
sequential changes in rock types.
- Epicontinental seas cover a large portion of the North American craton.
- On each side of the craton, we can find a transgressive sequence of sediments.
- There is no life on land at this time
- To the southwest of the craton are a series of islands
- Transcontinental arch: a series large, late Cambrian island arcs that extended to southern New
Mexico (bottom tip of land mass on above map).
- Erosion of the craton produced a lot of clean sandstone (good glass sand) in Wisconsin
- We can find examples Cambrian sand within the Bliss Sandstone (El Paso area)
- We also know that the Enchanted Rock area (Central Texas) had islands because of the Hickory
Sandstone (Mason, Texas)
Cambrian Climate
- During the Cambrian, the temperatures would have been warmer than today
- There would not have been advancing glaciers during this time
- There would have been no life on land at this time
Cambrian Big Bang Evolution
- At the Cambrian (542 MY), many different life forms suddenly appeared in the fossil record.
- This period represents the fundamental mysteries of the history of life on Earth and the fossil record.
- For billions of years, life was represented by simple life forms such as bacteria and algae.
- Then for a hundred million years, somewhat complex life forms appeared in the Upper Precambrian
Ediacaran Period (630 MY – 542 MY).
- There is some recent evidence that a few Ediacaran life forms may have survived beyond the
Cambrian 542 MY boundary
- Remember that this 542 MY boundary is based on trace fossils and the appearance of “small shelly
fauna” (advanced life)
- In 1993 Cambrian fossils were been found at Yakutat, Siberia to be older than (or before) the first
Cambrian trace fossils, yet younger than (or after) the Ediacaran fauna
. The fossils found here were primitive ancestors to sponges, mollusks and brachiopods.
- The Cambrian boundary has not yet been adjusted to fit this new location.
Complex Life Forms
- The Cambrian Big Bang continued with the rather sudden appearance of other diversified shelly
- For the first time, complex animals appeared with protective shells.
- New adaptations included: legs, claws, antennas, other appendages, eyes and mouths with teeth.
- All of these changes can be attributed to adaptive radiation
- Adaptive radiation: rapid speciation of a single or a few species to fill any ecological niche
- This is an evolutionary process derived by mutation and natural selection.
- Possibly either environmental with genetic causes
Environmental Changes Driving the Cambrian Adaptive Radiation
1 - Continued continental breakup allows more shallow water habitats to develop.
2 - Oxygen levels need to reach a critical level.
- A certain oxygen level is required to aerate tissues and to make structural components like teeth and
3 - Evolution of predators would favor species that have protective shells.
4 - Chemistry of the oceanic water may have changed to favor the precipitation of calcareous shells.
- Most of the ocean’s iron had been removed and placed into banded iron formations.
- Dolomite supply and deposition decreased.
- More dissolved oxygen in the water column
5 - Widespread submarine volcanism increased availability of energy and nutrients.
Genetic Causes of Cambrian Adaptive Radiation
- The various forms of mutations drive the process of evolving organisms that survive the changing
Chengjiang China
- The best Early Cambrian fossils are found in China
- In 1984, a large number of diverse Early Cambrian fossils were discovered here.
- The fossils here are really complex considering that complex life is just beginning on Earth.
- This implies that the Cambrian explosion may have occurred in as little as 10 MY.
- (Video clip of life in the Cambrian Chinese sea)
Sirius Passet, Greenland
- Also in 1984, fossils were discovered here which have the same age as fossils found in China
Burgess Shale Biota
- No discussion of Cambrian life is complete without discussing the Middle Cambrian Burgess Shale
- The Burges Shale was discovered in 1909 near Field, British Columbia, Canada
- This Middle Cambrian shale (515 – 520 MY) contains some of the best period examples of soft
bodied flora and fauna.
- The shale provides fossil examples of Earth’s complex animals.
- These animals had shells, heads, mouths, eyes, claws, legs and other appendages
- Many animals of the Burgess shale are “unknown phyla” - have no living organisms with their basic
body plan.
- This biota of invertebrates represents the root stock and basic body parts from all present day
invertebrates (and vertebrates).
- Life was much more diverse in terms of phyla during the Cambrian than today.
- The biota here 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
- By the end of the Cambrian, ancestors of all living phyla of shelly invertebrates had appeared (except
- No new shelly phyla have appeared since that time.
- The Early and Middle Cambrian fossils seem to imply early experimentation and then later
Phylum Chordata
- All chordate are bilateral animals related by possessing notochord: something resembling a backbone
- A notochord will eventually evolve into a backbone
Earliest Known Chordates
- Cathaymyrus diadexus age is 535 MY from China
- The chordate Yunnanozoon, figure 21.14, page 617 of text, has been reassigned to Phylum
- Next oldest known chordate (not vertebrate) found at the Burgess Shale, at 520 MY, is the 2-3 inch
Pikaia, a filter feeder (above).
Oldest Known Vertebrate
- Vertebrates: animals with backbones (covered notochord)
- Earliest known vertebrates are fish.
- Myllokunmingia is one of two of the oldest known vertebrate fish at 530 MY, found at Chengjiang,
- Haikouichths is also found at 530 MY
- (Video clip of Cambrian fish)
- Cambrian is also known as the Age of the Trilobites
- All orders of trilobites would evolve in the Cambrian
- Trilobites would make up +50% of the Cambrian fauna (542 MY – 488 MY).
- There would be more than 15,000 species
- The trilobites would have a wide variety of eye types.
- They are the world’s most popular fossil to collect.
- Trilobites would roll themselves up when faced with danger.
- Quite a few trilobites can be found near Llano, Brownwood and El Paso, Texas.
- Present day sow bugs and horse shoe crabs are not related to trilobites.
End of Cambrian
- The end of the Cambrian would be marked by colder temperatures and mass extinction of most of the
Ordovician Period (488 MY – 444 MY)
- As during the Precambrian, ancestral North America will again be subjected to tectonics and many
colliding land masses
- Such a tectonic collision is called an orogeny
- Orogeny: an episode of mountain building, usually associated with convergent zones.
- The results of an orogeny is intense crustal deformation accompanied by metamorphism and igneous
intrusions and thickening of the Earth’s crust.
- This is directly associated with colliding tectonic plates at convergent plate boundaries or subduction
- (Mountains form along convergent zones.)
Taconic Orogeny of the Appalachian Mountains (oldest)
- At 510 MY (Cambrian), the eastern US continental shoreline extended from New York to the
- During the Ordovician, Laurentia would remain south of today’s equator.
- Before this event, the Eastern US shoreline extended only from the Carolinas to New York.
- Offshore, an island arc called the Taconic Arch is headed toward Laurentia during the Early
- The Taconic Island Arc would first collide with the Canadian Maritime provinces
- The arc finished its collision (convergence) by 450 MY, extending the US coastline from New
England to Georgia.
- Remember that with convergent (subduction) zones, we find related igneous intrusions and the
Taconic Orogeny is no different
- The igneous intrusions from Georgia to New York all have similar age-dating of intrusions -460 to
440 MY (Taconic Orogeny).
- Later, two large masses begin approaching Laurentia from the eastern coast of the Iapetus Ocean –
the continent of Baltica and the Avalonia Islands (Acadian Orogeny)
- But we will have to wait for the Devonian for the US collision
- The early Appalachian Mountains created by the Taconic Orogeny will erode downwards before the
Acadian Orogeny
- Why is it that, over time, most mountains do not erode to a totally flat sea level plane?
- Mountains are characterized as rising above surrounding area; for this to happen, mountains must
have deep roots
- Mountains and mountain roots are a property of isostasy.
- Isostasy: the concept of the Earth’s crust floating on a dense underlying layer.
- This concept can be illustrated by a cork in floating water.
- As mountains erode, isostatic adjustments push the mountain roots upward.
- Isostatic rebound: the phenomena in which unloading (erosion) of the crust (mountains) causes the
crust to rise until it attains equilibrium.
- Thus older mountains will always be higher than the surrounding plains
- This is why mountains persist over millions of years.
- Ordovician sea levels were very high with transgressive seas over the North American craton, until
the end of the period
- The (Appalachian) Taconic Highlands now begin to erode downwards
- Thick sediments were deposited opposite the eastern subduction zone
- This would create the Queenstown Clastic Wedge
West Texas
- In the Early Ordovician, a large deposit of sand-grained filled dolostone were deposited by the seas,
called the sandy El Paso Formation in the El Paso area.
- In the Middle Ordovician, large deposits of dolostone were deposited by advancing seas, called the
Montoya Formation in the El Paso area.
- East of the El Paso area is found the Lower Ordovician Ellenberger Formation – a deep, thick
dolostone that has an associated 90 large oil fields and 50 major gas fields. Outcrops can be found
near Llano Texas.
Marine Life in the Ordovician
- Cephalopod mollusks grew to more than 18 feet in length.
- Brachiopods would increase in importance.
- Some trilobites survived into the Ordovician
- Plants would become well established in the seas
Class Agnatha – Fish of the Ordovician
- These are jawless fish that became common during the Ordovician Period
- These are some of the most primitive fish - they lack both a jaw and paired fins.
- There were six major groups called including Ostracoderms, a bony-skin fish that was about 10
inches long and lived only from the Cambrian to the Devonian (542 MY – 416 MY).
- Modern day examples include lamprey eels and hagfish
Ordovician Land Plants
- There is some evidence that primitive algae and lichens invaded the land masses
An Ordovician Ice Age and a Mass Extinction
- The third extensive continental glaciation will occur at the end of the Ordovician Period
- This will cause sea levels to drop (regressive seas)
- The glaciation also lowered water temperature
- The temperature and sea level drops will have a catastrophic effect on life; this probably lad 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
- This would include more than 100 families of marine invertebrates.
- There were basically no land forms of life yet.
Silurian Period (444 MY – 416 MY)
- Ancestral North America will soon again be 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
- Let’s begin the process at 450 MY in which the plates are approaching one another
- Baltica has collided with Canada and Avalonia is headed toward the eastern coast of the US
- But Avalonia will not yet collide with the US during the Silurian Period
- Meanwhile, the earlier Appalachian Mountains by the Taconic Orogeny are beginning to erode
Silurian Seas and Deposition
- Another period of high sea levels (transgressive seas) will cover most of North America (Laurentia).
- In the Michigan basin, large reefs would block seawater, resulting in thick salt deposits within the
Michigan basin.
- In Texas, large deposits of sandy dolostone (El Paso area) were deposited by the seas, called the
Fusselman Dolostone.
- To the east of El Paso, the Fusselman Dolostone is a major oil and gas producer in the deep wells of
West Texas.
Silurian Fish
- Sea life would now be filling as many niches as possible and we even have fresh water fish
- Silurian fish will take a major evolutionary step forward
- To develop further, fish needed to develop a jaw.
- Some suggest that the vertebrate jaw began with modifications of the first 2 or 3 gill arches.
- The first fish with jaws would develop during the Silurian Period
- Class Acanthodii were the first fish with jaws, known as spiny fish that grew up to 6 feet in length.
- Lived from Silurian to the end of the Paleozoic (444 MY – 251 MY).
- Class Placodermi is a Silurian armored fish that became extinct after only 50 million years of
- Group Arthrodires: was a giant predator that grew more than 20 feet long and had a giant head.
- Group Antiarchs: grew up to two (2) feet long and had over 100 species.
- The Silurian saw the development of large sea scorpions up to three feet long
- (Video clip of jawless fish and large sea scorpions)
- Later sea scorpions up to 10 feet long would evolve
- (Video clip of a giant sea scorpion)
First Invasion of Life on Land
- Even with the transgressive seas, there would be enough land available for life to invade
- Before there can be animal life on the land, there must be some kind of a food supply for them
- The first invasion of living organisms would take place during the Silurian
- And this occur about 430 MY ago by algae and vascular plants.
- Earliest known vascular plant is Psilopsids
- (Video clip of Silurian plants)
Insects (Arthropods)
- The earliest animals on land would be insects
- Oldest known fossil insect is the millipede (Silurian Age); we have found fossil footprints of some
giant millipedes.
- Also, there were many bizarre giant, scorpion-like insects that invaded the shorelines.
- (Video clip of scorpions on land)
Age of Corals
- The Silurian Period is often called the Age of the Corals because of the great abundance
End of Silurian Period
- The end of the Silurian Period is marked by a few groups of small marine creatures becoming extinct
Devonian Period (416 MT – 359 MY)
- We are now moving to the Late Paleozoic
- Life and Earth will undergo some major changes during this period
- The components for the Acadian Orogeny started at 450 MY (Ordovician) in which the plates of
Laurentia and Baltica and the island arc of Avalonia are converging
- The early Appalachian Mountains created by the Taconic Orogeny have eroded downwards
(Ordovician – Silurian)
- Baltica had converged with Canada and Avalonia was converging toward the eastern US coast
- The final convergence or Acadian Orogeny created a very tall Appalachian Mountains in the
Devonian Period
- Now we have the second generation Appalachian Mountains
Determining Ages of Mountains
- There are three different methods used to give the age of mountains
- 1) Age of mountains determined by the age of the rock deposition
- This is the time that the rocks actually formed but we have a problem: What if the deposition covered
several ages? Do you use the latest age?
- 2) Age of mountains determined by the orogeny that formed the mountains
- This represents the timing of the orogeny event. What if there was more than one orogeny?
- 3) Age of the mountains as determined by the topography
- What if the present topography was created by a renewed uplift?
- One or all three methods have been used to age-date a mountain
Antler Orogeny of Western US
- What else is going on that would eventually converge with Laurentia during the Devonian
- The Antler Highland mini-continent has been moving toward Laurentia
- But this Antler Orogeny will not occur until the end of the Devonian
Gold and the Antler Highland
- This ancient landmass forms a greater portion of the outcropping rocks of the state of Nevada.
- Some of the largest and richest US gold mining districts are found within this ancient Antler
- There is now a larger landmass created by the Taconic, Acadian and Antler orogenies
- We would now have a new huge continent called Euramerica (or Laurasia)
The Devonian Seas and Potash
- We will have mostly transgressive seas during the Devonian along with some times of regression
- Only a thin layer of Devonian rocks is found in Texas, the Canutillo Limestone in the El Paso area.
- Reefs blocked off most of the seawater from the Williston Basin in Canada which is the site of large
salt and world class potash deposits. (Potash is used for fertilizer)
- Land plants become widespread, large and diversified
- Forests first began along the river banks with shallow roots
- This will provide even more food for more animals to invade the lands
- Finally, tall trees (seed-bearing gymnosperms) with deep roots will evolve toward the end of the
- Earth is becoming slightly more familiar
Life in the Devonian Seas
- There will still be a few trilobite species in the seas
- Major changes were occurring in the shallow Devonian Sea especially with fish
- The Devonian Period is also known as the Age of the Fish
- All five (5) classes of fish would be alive at this time and there would be no new classes.
- Before we continue the lobe-finned fish, let’s review some of the fish that we have studied up to now:
acanthodians and Placodermi
- Let’s examine Devonian cartilaginous fish
- Class Chondrichthyes includes all of the cartilaginous fish (sharks, rays, etc.)
- This class includes a number of extinct but very weird shaped sharks including: Cladoselache,
Heliocoprion, Scissor-tooth shark, Stethacanthus and Farukatasu
- (Video clip of sharks and big fish)
-Let’s examine the remaining fish types that evolved during the Devonian
- Class Osteichthyes (bony fish) have two types of bony fish: lobe-finned fish and ray-finned fish
- Order Crossopterygii includes the lobe-finned Coelacanth, that first appeared in the Devonian and
was thought to be extinct 75 MY ago; but was rediscovered as a living fish in 1938.
- We can see some evolutionary changes with the lobe-finned fish
- They have articulated bones within stubby fins.
- They have muscles that extend into the fins.
- This is important because this would be the beginning of tetrapod limbs.
- Tetra is Greek for four and Podos is Greek for foot
- Tetrapod: Vertebrate animals having 4 feet or leg-like appendages (excludes fish)
- A lungfish is with the Order Dipnoi that was first seen in the Devonian.
- This is a living fossil that took another evolutionary step forward with external nostrils and lungs as
well as gills
- Lungfish have articulated bones in fins with muscles in the fins
- This includes the Devonian Panderichthys (416 MY – 359 MY) that had long frontal lobe-fins
- Let’s examine a freshwater fish that some scientists had earlier thought was the first tetrapod ancestor
of amphibians (found in the Devonian Period)
- Acanthostega at one time was thought to be an amphibian. But they probably had no lungs – just gills
like fish.
- Let’s also examine a present day tetrapod-like fish – the mudskippers of today
- “Mudskippers” are examples of modern day tetrapod fish (front limbs more developed than rear).
- (Video of a mudskipper battle)
- Other lobe-finned fish in the Devonian were showing their presence and may have been feeding
- It is suspected that Eusthenopteron fed out of the water along shoreline.
- Recent discovery of an air-breathing fish with front legs has been hailed as the missing link to
amphibians – Tiktaalik roseae
- Why do we suspect that fish may have walked on land?
- From a shallow water basin, we find +365 MY something large was walking in shallow water with
their widely separated footprints, preserved in today’s rocks.
- (Video clip of a walking fish Eusthenopteron)
- The first tetrapod ancestors of amphibians is found in the Devonian Period
- The labyrinthodonts called Ichthyostega had seven toes on its back fins (feet).
- We reviewed how the original fins of various creatures as they rapidly evolved into feet
- (Video showing possible evolution of fish into amphibians)
- At the end of the Devonian, another mass extinction would affect about 14% of Earth’s life forms.
- This resulted in the near collapse of all massive reef communities and one class of fish.
- Almost all warm water environments were affected but not the cool water environments.
- The primitive land plants were not affected by this event.
- The Devonian mass extinction may have taken a few million years to complete
- Causes: global cooling? Oceanic volcanoes? Other?
Mississippian Period (359 MY – 318 MY)
- Earth is preparing for its largest collision ever.
- Now at 327 MY, Euramerica (Laurasia) is headed toward Gondwana which will produce the Pangaea
- With this convergence, we will suture these masses together
- In the next period, tectonics will create the third generation of the Appalachian Mountains when
Africa will converge here
- The Mississippian Period is the last very widespread transgressive epicontinental sea.
- Many parts of “North America” will be covered by vast shale deposits
- We are not sure why so much mud was deposited here
- The Barnett Formation of Central and West Texas is one of such shale deposit
- Oil and gas wells are widespread within the Bartlett Shale.
- These wells will contribute +$100 Billion to the Texas economy
- Although the Mississippian is part of the “Carboniferous Period”, very little coal is associated with
this age in the US
- The epicontinental seas will contain abundant forms of life.
- The Mississippian is also called the Age of the Crinoids
- Blastoids became very common
- We know that amphibians were walking near water at this time
- 350 MY Mississippian footprints (probable amphibian) have been found in Canada.
- Amphibians had a major problem in that they had to lay gelatinous eggs in water.
- The next evolutionary step for vertebrates will be the development of the amniotic egg.
- These amniotic eggs (whether hatched inside the mother or in nests on the ground) provide the
parents (reptiles) greater opportunity for expanding their environment.
- (Video of the transformation of eggs)
- The first suspected reptile is a small lizard-like Westlothiana (350 MY) in Scotland
- Although we find a possible reptile here, the real “Age of the Reptiles” is the Permian Period (299
MY – 251 MY and different than the Age of Dinosaurs).
- The step from amphibian to reptile would take less than 60 MY
- At the end of the Mississippian Period, CO2 levels dropped from 1800 ppm to 300 ppm and world
temperatures dropped
- The Mississippian Period would end with a minor extinction of a few sea creatures
Pennsylvania Period (318 MY – 299 MY)
- This is the period of the “big collision”
- We will begin with the Allegheny Orogeny
- Now the latest Appalachian Mountains are part of the supercontinent Pangaea (PennsylvanianPermian Periods)
- It will be Permian times before the convergence with Africa will end
- Meanwhile, South America is converging with North America – the Ouachita Orogeny
- The results include the formation of the Ouachita Mountains of Arkansas and Oklahoma
- During the Allegheny Orogeny, the Llano area of central Texas will be uplifted from great depths
- Epicontinental seas are still present but less extensive than previous periods.
- These regressive seas will expose a series of islands in the western US
- The formation of Pangaea is nearly complete.
- Major coal deposits would form in the Eastern US and Texas.
- Evaporation would cause thick salt and potash deposits in New Mexico and Utah.
- Outcrops of Pennsylvanian limestone can be found in north-central Texas.
- During the Pennsylvanian Period, the craton (North America) would be part of Pangaea
- The Appalachians, Ouachita and Antler Mountains are present
- Major swamps are located along the equator, which will become vast coal deposits
- Even Texas has vast coal resources from these swamps
- (Video about the coal swamps)
- Trapped seas would collect in the basins
- Large deposits of potash would be created in New Mexico and Utah
- Pennsylvanian Period rocks can be found in central Texas
- With a large land mass and ongoing evolution near the equator, some changes are going on
- The first undisputed reptile is a small lizard-like Hylonomus that has been found in the 300 MY
(Pennsylvanian) Joggins Formation, Nova Scotia in Canada.
- The first mammal-like animals will appear now; we will discuss mammal-like in the Permian Period
- The Pennsylvanian Period is also known as the Age of Plants and Age of Giant Insects.
- New evidence suggests that insects may have developed wings in the Devonian Period
- Winged insects are common in the Pennsylvanian Period
- Dragonflies became giants, some with wingspans of 36 inches
- This period could also be called the Age of the Cockroaches since more than a thousand species were
present and they grew to be giants
- (video about insects – spiders, dragonflies, and centipedes)
- Earth will enter its fourth ice age at the end of the Pennsylvanian Period
- This will cause a minor extension with some marine fauna
Permian Period (299 MY – 251 MT)
- The Allegheny Orogeny will be completed and we now have the supercontinent of Pangaea
- And the Appalachian-Caledonian Mountain ranges were created
- For half of the Permian Period, Earth will endure its fourth ice age- Fewer swamps will be around for
most of the Permian
- Glaciers and deserts are common for most of this period
- There were fewer transgressive seas
- And the Appalachian- Caledonian Mountains will present a barrier for biodiversity
- During this period, only the western 1/3 of the US was under shallow seas.
- In West Texas, there is a large evaporate basin
- In this basin, the thick Castile Gypsum will be deposited
- The West Texas Permian Basins would be inland seas with the seawater coming from the west
- Large reefs (shelves) would surround these seas
- El Capitan in the Guadalupe Mountains is actually a world famous Permian reef.
- The Permian Basin is famous for its huge oil and gas deposits
- In the Utah area is the Phosphoric Sea where valuable deposits of phosphates (fertilizer) will be
- There are extensive Permian deposits of sandstone and limestone in North-central Texas.
- Animal life expanded on the lands
- Large primitive amphibians lived along the shorelines of Texas:
- Seymouria baylorensis, from Baylor County, (North) Texas
- Eryops and Cacops from Archer County, (North) Texas
- Diplocaulus from near Abilene, Taylor County, Texas is a famous Texas fossil.
- We should mention the freshwater reptile mesosaurs of African and South American rivers
(remember continental drift)
- The Permian Period is also known as the Age of the Mammal-like Reptile (not dinosaur)
- And we will see that at the end of the Permian – this will be a failed life form for Earth
- The finned-back Pelycosaurs are mammal-like reptiles
- This includes the carnivorous Dimetrodon and Edaphosaurus an herbivore
- Dimetrodon skeletons have been found Archer County, North Texas.
- Cynogathus are mammal-like reptiles of African- South American fame (continental drift fame)
- (Video on big reptiles and video on mammal-like reptile)
- What do we mean by mammal like?
- The mammal-like animals had several mammalian skeletal characteristics”
- Primitive differentiation of teeth, like mammals (all other animals have same style teeth)
- They have several mammalian skeletal characteristics.
- No true mammals have been found before the Mesozoic Era.
- (Video on teeth)
- Now the therapsids will evolve
- (Video – Late Permian)
- The world environments become largely deserts
- (Two videos on changes)
- The end of the Permian Period would result in the largest mass extinction event ever recorded on
- (Video clip)
Late Ordovician (444 MY) Mass Extinction
- There were times when Earth was not a very friendly place for many forms of life.
- At the late Ordovician, about 12% of Earth’s life forms would become extinct.
- This would include more than 100 families of marine invertebrates.
- There were basically no land forms of life yet.
Late Devonian (359 MY) Mass Extinction
- At the end of the Devonian, another mass extinction would affect about 14% of Earth’s life forms.
- This resulted in the near collapse of all massive reef communities and one class of fish.
- Almost all warm water environments were affected but not the cool water environments.
- The primitive land plants were not affected by this event.
Late Permian (251 MY) Mass Extinction
- This event would mark the largest mass extinction event ever recorded on Earth.
- More than 52% of Earth’s “families” became extinct.
- This event marks the end of the Permian Period and Paleozoic Era.
Permian Life Forms That Became Extinct by 251 MY Ago
- 90% -95% of all marine invertebrate species died out (shallow water).
- Only one of the many species of Crinoids survived (shallow water).
- All blastoids disappeared (shallow water).
- 80% of all brachiopods disappeared (shallow water).
- Almost all gastropods (sea snails) disappeared (shallow water).
- 8 out of 27 orders of insects disappeared (land environment).
- Two orders of coral disappeared (shallow water).
- 75% of all reptiles disappeared (land environment)
- 67% of all amphibians disappeared (water and land environments)
- Another entire class of fish disappeared (marine environment)
- All trilobites disappeared (all water environments).
Timing of the Permian Period Mass Extinction
- This extinction was not instantaneous but occurred over a period of less than 8 million years.
- Succeeding Mesozoic life forms would have a very low diversity but the surviving species would
tend to be very abundant and widespread.
Probable Cause of the Permian Mass Extinction
- We do not know for certain.
Types of Extinctions
- Extinction: the planet-wide disappearance of a species or higher taxonomic group.
- This is the ultimate fate of all species.
- This is a continuous process as recorded in the fossil records.
- Looking back at the Phanerozoic Era, we have noticed five severe mass extinctions.
- Background Extinctions: continued extinction of species.
- Mass Extinctions: twice the background rate
- Minor Mass Extinction: same as above (mass extinction); a good example would be the decrease in
many species at the end of the last Ice Age.
Time to Complete A Mass Extinction
- From a few months to a few million years.
Significance of a Mass Extinction
- This signifies a planet-wide environmental or ecological problem.
- For one species, a mass extinction is bad but for another species – a mass extinction of their
competitors is good.
- The extinction of a large number of dominant species is instrumental in the expansion of “minor”
species to fill the niche left open by the mass extinction.
Theories of Mass Extinctions
- Most are related to catastrophic changes in the atmosphere; or
- Catastrophic changes in the hydrosphere
- Many geologic events can severely affect either one or both of these spheres.
Meteorite Impacts
- These can have a major impact on Earth’s atmosphere, with the addition of gas, dust and chemicals.
- The hydrosphere and atmosphere could be severely impacted by sudden global heating and global
Related to Massive Volcanism
-Flood basalts: huge flows (thousand of cubic miles) of basalt from fissures.
- These add huge quantities of greenhouse methane and CO2 gases to the atmosphere
- The Permian Siberian flood basalts added 500,000 cubic miles of basalt to the Earth’s surface.
Continental Glaciation
- This can cause major changes in sea levels that affect cooler ocean water and world temperatures.
- The formation of a super-continent can cause major changes in ocean currents and on climate.
- Also postulated are problems with magnetic reversals and supernovas.
- However, there has never been a total extinction during the Phanerozoic Eon.