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

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By Loren E. Babcock

Chapter 10

Paleozoic World

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.

Early Paleozoic

Cambrian overview

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.

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.

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.

Early Paleozoic

Exceptional preservation of fossils and

Cambrian biodiversity

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.

Early Paleozoic

Cambrian Predatory-prey System

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


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.

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.

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.

Early Paleozoic

Ordovician marine life

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.

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.

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.

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.

Middle Paleozoic

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.

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.

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.

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.”

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.

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.

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.

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


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.

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.

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.

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.

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


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.

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.

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