Op ch13 lecture_earth3, Understanding of Earth history,

Earth: Portrait of a Planet
3rd Edition
Chapter 13
Norton Media Library

AB

Prepared by

Ronald Parker
Earlham College Department of Geosciences
Richmond, Indiana

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Earth Has a History
Geologic materials record enormous changes.
 Earth is a complex, evolving system.


Physical and biological systems continuously interact.
 Earth constantly changes and has done so through time.


Species arise, flourish and disappear forever.
Continents rift, drift and collide.
Ocean basins open and close.
Sea-level rises and falls.

Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 13: A Biography of Earth

Methods for Studying the Past


Historic Earth changes are measured by…
Orogenic events.
 Sea level.
 Climates.
 Living organisms.
 Continental positions.
 Plate boundaries.
 Chemistry.


Atmosphere.
Ocean.




Depositional environments.

These changes are recorded in rocks.




Earth history is not always easy to decipher.


Much of the record of past events is incomplete. Why?
The record didn’t accumulate continuously.
Erosion destroys the record with age as a variable.

Younger rocks are better preserved; older rocks less so.





Earth history is not always easy to decipher.
Despite erosion, there is still an abundance of evidence.
 This evidence is often readily observed by looking at rocks.






Ancient orogens – Former mountain belts.
Igneous activity, deformation and metamorphism.
 Thick sedimentary deposits filling foreland basins.
 Ancient orogenic belts expose deeply buried rocks.






Clear evidence of continental growth over time.


Continents grow by addition along edges.
Continental interiors are older.
Rocks become younger
toward margins.





Recognizing depositional environments.




Successions of strata record changes
in depositional settings.

Recognizing sea-level changes.
Sediments record sea-level flux.
 Shallow and deep environments
create distinctive sediments.






Changing continental positions are preserved.
Paleomagnetism captures paleolatitude.
 Ocean width changes by reversing sea-floor anomalies.
 Rock and fossil distributions compare across oceans.






Paleoclimates – Rocks preserve ancient climates.
Tropical – Extensive coral reefs.
 Sub-tropical – Extensive deserts.
 Polar – Extensive glacial deposits.




Climatic belts expand and contract.
Greenhouse Earth.
 Snowball earth.




O/16O isotopic ratios preserve
ancient temperatures
18





Evolution – Fossils preserve changes in Earth’s life.
Sedimentary rocks preserve fossil ecosystems.
 Organisms inhabiting Earth have obviously changed.


Over geologic time, most species have exhibited both…

Trends toward specialization.
Catastrophic extinctions.



The Hadean Eon


Geochronology dates the age of Earth to 4.57 Ga.


Based on ages of meteorites akin to planetesimals.

Continental crustal rocks date from 3.8 Ga.
 The time between 4.57 – 3.8 Ga is the Hadean Eon.


Named for Hades, the Greek god of the underworld.
 Began with formation of Earth by planetesimal accretion.




The Hadean Eon
Earth was heated by impacts and radioactive decay.
 Earth was hot enough to partially melt by ~ 4.5 Ga.




The molten Earth underwent chemical differentiation.
Gravity pulled molten iron into the center.
The ultramafic mantle remained as a thick shell.



The Hadean Eon
After differentiation, Earth smashed a proto-planet.
 The size of Mars, this planet blasted…


A sizeable chunk of Earth’s mantle.
 Much of the proto-planet’s mantle.




Debris from the collision formed a ring around Earth.



The Hadean Eon
This debris coalesced to form the moon.
 When 1st formed, moon was much closer (20,000 km).
 Today it is 19x farther away (384,000 km).




The Hadean Eon


Earth was inhospitable; a molten surface.


Evidence of solidified igneous rock dates from 4.4 Ga.
This evidence is from zircon grains, not a whole rock.



The Hadean Eon


Volcanic outgassing created a deadly atmosphere.





N2, NH3, CH4, H2O, CO, CO2 and SO42- were components.
This atmosphere had a greater density that today’s.

Early formed crust was bombarded by meteorites.


Meteorite impacts were abundant between 4.0 and 3.9 Ga.
This would have destroyed early formed crust.
Oldest evidence of crust is 4.03 Ga.



The Hadean Eon


The first oceans formed as rain from the skies.
Liquid water required cooling of the surface.
 First evidence of oceans from marine sediments ~ 3.85 Ga.




The Archean Eon
Time of significant change to planet Earth.
 ~3.8 Ga, Earth had cooled to form lithosphere.


Intense meteorite bombardment ceased.
 Portions of the rock record begin to survive.




The Archean Eon


Had plate tectonics started yet? 2 models.
Many small microplates, island arcs and hot spot volcanoes
rapidly formed and subducted crust.
 Archean lithosphere was too hot to subduct; hot spot plume
volcanics dominated formation of crust.




The Archean Eon


Volume of continental crust increased dramatically.
85% of modern continental area present by end Archean.
 Signals full development of plate tectonic processes.




The Archean Eon


How did continental crust form?


Low density felsic rocks formed above subduction zones.
Felsic crustal blocks grew via continental collision.
Felsic sediments accumulated near continental crust.



Mantle hot spots built mafic volcanoes.



The Archean Eon


How did continental crust form?


Continental crust is too buoyant to subduct.
Jams subduction trenches.
Shuts off subduction.
Creates thickened, uplifted continental crust.



Frequent collisions sutured volcanic arcs, hot spots and
sedimentary debris together as protocontinents.



The Archean Eon


The 1st cratons had formed by 2.7 Ga. Cratons are…
Long-lived blocks of durable continental crust.
 Too buoyant to subduct, these blocks persist over time.


Cratons are the interior core of modern continents.
 Continents grow as rocks are added to cratons.




The Archean Eon


Archean cratons consist of 5 principle rock types.
Gneiss – Hi-grade metamorphics from Archean collisions.
 Greenstone – Metamorphosed fragments of mafic rocks.
 Granite – Magmas from partial melting of the crust.
 Graywacke – Sedimentary debris derived from arcs.
 Chert – Silica precipitated in the deep sea.




The Archean Eon


Archean shallow sediments are poorly known.
There were few shallow depositional settings, or…
 Few examples have survived destruction by erosion.




Sedimentary processes were clearly operating.


Transport rounded sediment grains.



The Archean Eon


Life first appeared during
the Archean. Evidence?
Biomarker molecules.
 Isotopic signatures.
 Preserved fossil cells.




Clear evidence of life in
rocks dated to 3.5 Ga.




Life may have started earlier.

Oldest undisputed bacteria
fossils ~ 3.2 Ga.



The Archean Eon


Rocks after 3.2 Ga contain stromatolites.
Layered mats of cyanobacteria (blue-green algae).
 Sediments stuck to mucous coatings on algal filaments.




Photosynthesis changed Earth’s atmosphere.


Converts CO2 and H2O to organic matter and free oxygen.



The Proterozoic Eon


Protero = first; zoic = life.


Named before Archean life was discovered.

~ 2 Ga (2.5 to 0.542 Ga); almost ½ of Earth history.
 The unfamiliar Archean world changed to…


Fewer, larger lithospheric plates.
 Larger continental landmasses.
 An oxygenated atmosphere.




The Proterozoic Eon


New continental crust formed, but at slower rates.
90% of Earth’s continental crust by the middle Proterozoic.
 Continents grew by addition of volcanic arcs.
 Continents cooled and strengthened to become cratons.




The Proterozoic Eon


Case History: The assembly of North America.


A large area of Pre-Cambrian rocks outcrops in Canada.
This constitutes a shield – a low-lying area of Pre-C rocks.



The cratonic platform occurs to the S and W of the shield.
Phanerozoic strata cover the Pre-C shield.
Shield rock underlies much of U.S.

Encountered by drilling.
Exposed in the Grand Canyon.



The Proterozoic Eon


Canadian Shield consists of many distinct blocks.
Sutured Archean crustal blocks form the shield interior.
 Added volcanic arcs and crustal slivers extended




The Proterozoic Eon


Continental collision created Pre-C supercontinents.
Rodinia – Formed ~ 1 Ga.
 The Grenville Orogeny formed an extensive mountain belt.




Pannotia – A short-lived supercontinent ~ 600 Ma.



The Proterozoic Eon


Atmospheric oxygen (O2) skyrocketed 2.4 to 2.2 Ga.


Currently, O2 is 21% of the atmosphere.



Before 2.2 Ga, detrital pyrite in sediments indicated no O2.

Redbeds (red from Fe-oxides) don’t appear before 2.2 Ga.
 Banded Iron Formations (BIFs) – Fe dissolved in the ocean
reacted with O2, forming world wide iron oxide deposits.




The Proterozoic Eon


Atmospheric O2 permitted diversification of life.


Aerobic respiration more efficient; allowed multicellular life.
Without O2, only single celled organisms possible.
Eukaryotic (nucleated) cells evolved by at least 1.0 Ga.



The possibility of a land-dwelling biota.
O2 made formation of the ozone layer possible.

Ozone absorbs deadly ultraviolet (UV) radiation.
Prior to the ozone layer, exposed land was bathed in UV.



The Proterozoic Eon


Over the last 500 Ma of the Proterozoic…


A gigantic leap in biological complexity.
Simple organisms gave way to complex ones.



Ediacaran fauna – Unusual soft-bodied fossils.
Preserved in end Proterozoic sediments.
 Multicellular invertebrates
resembling worms and jellyfish.




The Proterozoic Eon


Ediacaran fauna arose in conjunction with 2 events.
The assembly and breakup of the Pannotia.
 Global cooling possibly resulting in a “Snowball Earth.”


Most of the world bears evidence of being frozen.
Life diversified rapidly after snowball conditions waned.



The Phanerozoic Eon
Phaneros = visible; zoic = life.
 The most recent 542 Ma of Earth history.




Began with appearance of diverse hard-shelled organisms.
Hard-shells vastly increased fossil preservation.
Made possible a more complete archive of life on Earth.



The Phanerozoic Eon


The Phanerozoic is divided into 3 Eras.
Paleozoic – Ancient life.
 Mesozoic – Middle life.
 Cenozoic – Recent life.




Eras emphasize changes in Earth’s biota.



The Phanerozoic Eon


Tectonic plates and continental blocks rearranged.
Ancient changes in paleogeography have been deciphered.
 The map of Earth looked different throughout the Eon.


New supercontinents formed and rifted apart.
 Numerous orogenic belts were created and eroded.




The Phanerozoic Eon
Phanerozoic sea-level (SL) has changed often.
 SL highstands flooded continental interiors.






Rising SL (transgression) initiated sediment deposition.

SL lowstands exposed
continental margins.


Falling SL (regression)
initiated erosion or
non-deposition.



The Phanerozoic Eon
SL cycles are marked by large-scale unconformities.
 Stratigraphic sequences reflect SL highstands.


Rising SL invaded further inland with passing time.
 Falling SL moved progressively outward from the interior.
 Unconformities…


Become younger toward
continental interiors.
Bound less time in the
interior; more time along
the margins.



The Early Paleozoic


Cambrian and Ordovician Paleogeography:


Rifting of Pannotia left 4 large continental fragments.
Gondwana – (S. America, Africa, Antarctica, India, Australia).
Laurentia – (N. America and Greenland).
Baltica – (Europe).
Siberia.

 Part

of Gondwana was
over the South Pole
in the late Ordovician.
Marked by glacial deposits.



The Early Paleozoic


The rifted continents developed passive margins.
 Rising seas flooded expanses of continental crust.


Epicontinental seas were shallow, warm and sunlit.
Thriving marine life preserved as fossiliferous sediments.



The Early Paleozoic


Subduction carried a volcanic arc toward Laurentia.
 Mid-Late Ordovician: continental crust jammed the trench.
 Passive margin sediments were deformed by the collision.
 A volcanic arc was welded onto the margin.
 The “Taconic Orogeny” was the 1st Appalachian event.




The Early Paleozoic


Cambrian and Ordovician Life Evolution:
Earliest Cambrian – Hard shells appeared for the 1st time.
 Massive diversification followed: the “Cambrian explosion.”
 Reflects the evolution of a complex ecosystem.


Plankton, deposit feeders, giant predators.



The Early Paleozoic


Cambrian and Ordovician Life Evolution:


Life during the Ordovician included several “firsts.”
The 1st vertebrates were jawless fish (agnathans).
The 1st crinoids (flower-like echinoderms).
The 1st green algae and primitive land plants.

The end of the Ordovician witnessed a mass extinction.
 The seas roiled with life, but there was no life on land yet.




The Middle Paleozoic


Silurian and Devonian Paleogeography:


Silurian climate warmed to create greenhouse conditions.
Epicontinental seas expanded.

Gigantic reef complexes developed in normal salinity water.
Thick evaporite deposits accumulated in isolated ocean basins.
The Taconic mountains eroded away.
Sediment was shed to either side of the eroding source.








A 2nd eastern orogenic phase occurred in the Devonian.
The Avalon microcontinent was welded onto North America.
Large mountains marked the Acadian-Caledonian Orogeny.
Vast sediment aprons spread outward from the uplift.







In the west, thick passive-margin sediments accumulated.
An island arc smashed this margin in the Late Devonian.
This created the Antler orogenic belt.





Silurian and Devonian Life Evolution:
New species replaced those lost to extinction.
 Vascular land plants evolved and spread across Earth.


Internal water transport systems.
Woody tissues.
Seeds.
 Land

plants changed Earth.





 Fish

rapidly evolve and proliferate.

Jawed fish.
Boney fish.
 The

1st land animals
followed plants.
Scorpions.
Spiders.
Insects.
Crustaceans.





 At

the end Devonian, the 1st amphibians appeared.

Walked on legs.
Breathed air with lungs.



The Late Paleozoic


Carboniferous and Permian Paleogeography:
Climatic cooling followed the Mid-Paleozoic greenhouse.
 Seas regressed from continents.
 Clastics choked out carbonates.
 Thick coals formed equatorially.
 Ice sheets spread across Gondwana.




The Late Paleozoic


Continental collisions formed the supercontinent Pangaea.
 Gondwana collided with Laurentia (Alleghenian orogeny).


North America collided with Africa.
The Gulf Coast collided with
South America.


Collisions were oblique.
Folding.
Thrust faulting.
Strike-slip faulting.



The Late Paleozoic




The Appalachians preserve several types of geology.
Thin-skinned thrust faulting over basement rock.

Produced the Appalachian fold-thrust belt (Valley and Ridge).
Deformation above a large horizontal detachment fault.
A more intensely deformed and intruded metamorphic core.



The Late Paleozoic




The assembly of Pangaea had other tectonic effects.
Deformation was transmitted across Laurentia.

Basins and uplifts formed in the mid-continent.
Hercynian orogen - Africa
collided with S. Europe.
Ural Mountains – Europe
collided with Siberia.
China attached to
southern Siberia.



The Late Paleozoic




Pangaea was a massive supercontinent.
The interior was a vast desert far from ocean moisture.

Large deposits of red (oxidized) dune and fluvial sandstones.
Large accumulations of evaporites.



The Late Paleozoic


Carboniferous and Permian Life Evolution:


Life continued to evolve.
Dense tropical wetlands hosted vegetation and giant insects.
Amphibians diversified.
Reptiles appeared for the 1st time.

The amniote egg permitted reproduction away from water.
Reptiles populated previously inhospitable environments.



The Late Paleozoic


Carboniferous and Permian Life Evolution:


The Paleozoic ended with the Permian extinction.
90% of all marine species disappeared.
Some evidence links the extinction to a bolide impact.



Early and Mid-Mesozoic Era


Triassic and Jurassic Paleogeography:
The supercontinent Pangaea lasted 100 million years.
 Pangaea began to rift late Triassic to early Jurassic.


Rifting started in the North Atlantic.
A thin narrow ocean had
opened by the end Jurassic.
This basin accumulated
thick evaporite deposits.





Pangaea's interior was hot and dry.
 Greenhouse climates cooled by the mid-Jurassic.


Transgression flooded much of the Rocky Mountain region.







Western North America was an active margin.
Subduction created island arcs.
Collision added arcs and
microcontinents to N. America.

Sonoma orogeny – Perm – Tri.
Nevadan orogeny – Late Jur.





Triassic and Jurassic Life Evolution:


New species filled niches vacated by extinction.
Corals became dominant reef builders.
Gymnosperms proliferated.
Reptiles diversified.

Plesiosaurs – Swimming reptiles.
Pterosaurs – Flying reptiles.
Turtles appear.





By end of the Triassic the first true at dinosaurs appeared.
 Dinosaurs differ from other reptiles in significant ways.


Legs are positioned beneath their bodies.
They bear evidence of warm bloodedness.


By the end Jurassic giant sauropods were abundant.





The 1st feathered birds (archaeopteryx).
 The 1st ancestors of mammals appeared at Triassic.


They resembled small rat like creatures.



The Late Mesozoic


Cretaceous Paleogeography:


Climate continued to warm; seas flooded the continents.
An ocean connected the
Gulf of Mexico to the Arctic.
Epicontinental seas
accumulated limestone
and sandstone.



The Late Mesozoic




Breakup of Pangaea continued through the Cretaceous.
South America separated from Africa.
Antarctica separated from Australia.
India broke from
Gondwana and raced
toward Asia.
Passive margins
developed along
the Atlantic.



The Late Mesozoic




In western North America the Sierran continental arc grew.
Arc volcanoes have long eroded away.
Roots of the arc are exposed as the Sierra Nevada batholith.
An accretionary prism grew on the overriding plate.
These sediments form the present day Coast Range.



The Late Mesozoic


Cretaceous
Paleogeography:


Sierran Arc compression
initiated the Sevier orogeny.
Large thrust faults moved to
the east of the arc.
The Sevier fold and thrust
belt elevated the Canadian
Rockies.
A large foreland basin
formed east of the thrusting.



The Late Mesozoic




Laramide Orogeny – Late Cretaceous basement uplifts.
Reverse faulting due to continued compression to the west.
Uplifts appear in Wyoming, Colorado, Utah and Arizona.

 Basement faulting folded overlying Paleozoic strata.
 Results: Large monoclines and uplift of Rocky Mountain Front.



The Late Mesozoic
Orogenic events suggest complicated feedbacks.
 Rifting of Pangaea led to mid-ocean ridges (MORs).
 Seafloor spreading operated 3x faster.
 Huge submarine plateaus formed from flood basalt.




The Late Mesozoic
The Late K was a time of unusual volcanic activity.
 Attributed to unusually large hot spots.
 Late K volcanism influenced the climate.




Volcanic CO2 (8x modern values) warmed the atmosphere.



Melting ice caps contributing to sea level rise.



The Late Mesozoic


Cretaceous Life Evolution:


Teleost fish appeared and became dominant.
Symmetrical tails, specialized fins, short jaws, rounded
scales.

Swimming reptiles and gigantic turtles swam the seas.
 Angiosperms (flowering plants) appeared and spread.


Produce seeds rapidly.
Insects facilitate pollination.
Hardwood trees proliferated.



The Late Mesozoic


Cretaceous Life Evolution:


Dinosaurs reached their evolutionary peak.
Inhabited almost all environments on earth.
Social herds of grazing dinosaurs roamed the plains.
Large carnivores fed upon the herbivores.
Pterosaurs soared overhead, birds began to diversify.



Mammals developed larger brains and specialized teeth.



The Late Mesozoic


The K-T (Cretaceous–Tertiary) boundary event.


There is abundant evidence of catastrophic change.
Instantaneous global change in fossil assemblages.
Sudden mass extinction of most species on earth.

The dinosaurs which had ruled the planet for 150 Ma vanished.
90 percent of plankton disappeared.
75% of plant species vanished.



The Late Mesozoic


Catastrophic impact by a 10 km comet or meteorite.
 The Chicxulub crater lies beneath the northern Yucatan.


Radiometric dating indicates the crater formed at ~ 65 Ma.
100 km wide; 16 km deep.


Periodic impacts are
likely contributors to
other extinctions.



The Late Mesozoic




Evidence for an impact end to the Mesozoic?
Thin clay interrupts deep-sea chalk at the K-T boundary.

This suggests that, for a short time, all plankton died.
Iridium in the clay is rare on Earth; common in meteorites.
Iridium enriched clay found at the K-T boundary worldwide.
The clay contains shocked quartz and tiny glass spheres.
An immense impact best explains these features.



The Late Mesozoic




What did the impact do to Earth?
The impact blasted debris into the sky from a huge crater.
It created a gigantic tsunami (2 km high).
The blast of hot air set forests on fire.



The Late Mesozoic




What did the impact do to Earth?
Dust in the atmosphere would have blotted out the sun.
Sulfate from vaporized gypsum created sulfuric acid rain.
Lack of sunlight shut down photosynthesis.



The Cenozoic Era
Cenozoic (65 Ma-present) – The most recent history.
 Cenozoic Paleogeography:


During the last 65 Ma, Earth has continued to change.
 The final stages of the breakup of Pangaea.


Australia detached from Antarctica.
Greenland separated from North America
The North Sea formed between Britain and Europe.
Sea-floor spreading continued to open the Atlantic Ocean.



The Cenozoic Era


Cenozoic Paleogeography:


Fragments of Gondwana collided with Europe and Asia.
Closed the Tethys Ocean.
Deformed and uplifted the Alpine-Himalayan chain.



The Cenozoic Era




Pacific margins of the Americas continued convergence.
Andes grew as a continental volcanic arc.
Rocky Mountains grew by thrusting and basement uplift.



The Cenozoic Era




The large Farallon plate was almost completely consumed.
A transform fault replaced part of the Farallon trench 40 Ma.
The San Andreas / Queen Charlotte fault system formed.
The Juan de Fuca plate remains as a Farallon remnant.



The Cenozoic Era




East-west extension started to
stretch southwestern N. Am.
A broad continental rift stretched
and thinned the crust.
This region is called the Basin
and Range Province.

Elongate N-S linear mountain
ridges (ranges).
Ranges are separated by N-S
linear valleys (basins).
This geometry reflects normal
fault block rotation.



The Cenozoic Era


Global climate has gradually cooled since the Cretaceous.
 The Antarctic ice cap reappeared in the early Oligocene.
 Continued cooling led to the formation of grasslands.
 The Isthmus of Panama emerged 2.5 Ma.


Isolated circulation between the Atlantic and the Pacific.
Permitted the Arctic Ocean to freeze.



The Cenozoic Era




The Quaternary Period (2 Ma – present): Cool climate.
Pleistocene ice ages – Continental scale glaciation.

Glaciers have advanced and
retreated at least 20 times.
Modern landscapes sculpted
by glacial erosion /deposition.
Climate warmed 11 Ka; Earth
is currently in an interglacial.



The Cenozoic Era




The Quaternary Period (2 Ma – present): Cool climate.
Pleistocene ice ages – Continental scale glaciation.

During ice ages,
SL fell exposing
continental shelves.
Shelves acted as
land bridges for
human and animal
migration.



The Cenozoic Era


Cenozoic Life Evolution:
After the K-T boundary, plant life recovered.
 Forests of angiosperms and gymnosperms reappeared.
 The 1st grasses appeared in the middle Cenozoic.
 Dinosaur descendants (birds) diversified and spread.




The Cenozoic Era


The Cenozoic is known as the age of mammals.
 Mammals rapidly diversified to fill vacated niches.
 By mid-Cenozoic huge mammals appeared.


Woolly mammoths.
Giant beavers.
Ground sloths.



Late Cenozoic, human ancestors 1st appeared.



The Cenozoic Era


Ape-like primates diversified in
the Miocene (~ 20 Ma).
 The 1st human-like primate
appeared about 4 Ma.
 The first members of the genus
Homo appeared to 2.4 Ma.




The Cenozoic Era




What sparked the evolution of the genus Homo?
Climate changes that led to the spread of grasslands?

Permitted departure from the trees.
Life on the ground allowed more time for infant development.
This permitted growth of larger brains.
 Homo erectus appeared ~ 1.6 Ma.
Made stone axes.

Homo sapiens appeared ~ 500 Ka.
 Modern humans appeared ~150 Ka.
 Many giant mammals died off 10 Ka.


Climatic change?
Hunting pressure by humans?


The Geologic Time Scale



W. W. Norton & Company
Independent and Employee-Owned

This concludes the Norton Media Library
PowerPoint Slide Set for Chapter 13

Earth: Portrait of a Planet
3rd Edition (2008)
by Stephen Marshak

Op ch13 lecture_earth3, Understanding of Earth history,

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