Earth

1
Earths Evolution Through Geologic Time
2

• Why is Earth Unique?
• Life is ubiquitous! Its everywhere!
• Just the right size gravitational forces hold
  a relatively thin atmosphere
• Earth possesses a metallic core supports a
  magnetic field protecting life
• from lethal cosmic rays
• Just the right distance from the sun 93
  million miles allowing water
• to exist in all three phases (solid, liquid,
  gas)
• Just the right time enough time for
  microorganisms to photosynthesize an
• oxygen-rich atmosphere 2.2 billion years ago
• Just the right time asteroid impact about 65
  million years ago creates
• mass extinction allowing the proliferation of
  mammals
• Plate Tectonic Processes recycling
  lithospheric material

So, how did earth become what it is today?
3
65 my
88 of Geologic Time
186 my
251 my
291 my
542 my
4600 my
4
I
The Geologic Time Scale.

• Write down the Geologic Time Scale.
• Include in your time scale the following
• Eons
• Eras
• periods
• Epochs for the Cenozoic and
• Tertiary periods
• 2. Write a mnemonic phrase for the periods

10
5
Start of the Precambrian 4.6 by

• explosion from a single point
• universe expanding

• contribution of heavy
• elements

• cooling H, He

• fusion begins

• more contraction / accretion

• contraction prtosun

planetesimals
chemical differentiation
Earth
Primitive atmosphere starts to form during
the Hadean Eon
6
The Hadean Eon (4.6 b.y.) hellish conditions
As the Earth begins to cool

• In Earths early formation
• atmosphere H, He, CH4, NH3, CO2, H2Ovapor
• weak gravity H, He is lost to space
• T-Tauri phase (high solar winds)
  removed all the other gasses

• Earths First Enduring Atmosphere
• produced by outgassing gasses escape from the
  Earths interior
• outgassing produced by hundreds of active
  volcanoes
• Earth was in a fluid state, releasing high
  amts of gas
• Earths atmosphere from outgassing
• water vapor, CO2, SO2, minor amounts of other
  gasses

So, where is the oxygen?
7
Oxygen in the Earths Atmosphere

• Increasing oxygen-generating organisms
• oxygen increased steadily to stable
  concentrations
• the oxygen explosion forms ozone (O3)
• formed in the stratosphere
• protects life (DNA) from UV radiation

Stable O2 levels by 1.5 b.y.

• Oxygen reacts with iron, creating banded iron
• formations (3.5 2 b.y. ago)
• iron oxygen --gt RUST
• alternating layers of chert and iron-rich
• rocks

Banded Iron Formations

• Photosynthesizing bacteria release oxygen into
  the
• water---- 3.5 billion years ago
• CO2 H2O Energy sun --gt Oxygen

Cynobacteria (blue-green algae)

• A cooling earth ? Condensing water vapor
  (clouds)
• and rain, producing the oceans (filling in low
  areas)

4.0 b.y.
8

• Banded Iron Formations
• Deposited during the Precambrian Eon
• 3.5 to 2 billion years ago

9
Evolution of the Earths Oceans
CO2 (major greenhouse gas) readily soluble in
seawater (the oceans)
CO2 H2O Ca2 ? CaCO3 (Limestone)
Organisms extract CaCO3? shells and
die producing LS-sediment
Atmospheric CO2
Dissolved ions in the ocean

• Earths atmosphere rich in H2S , CO2, SO2
• Rain H2S, CO2, and SO2 ? ACID RAIN
• Highly acidic rain ? accelerated weathering
• Na, K, Ca, Si ions carried into the ocean
• Some dissolved ions ppt ? chemical sediment
• Other ions increased ocean salinity

About 90 of the current volume of seawater was
contained in the ocean basins (4.0 b.y.)
10
White Cliffs of Dover, England
Thick chalk sequence (CaCO3) deposited during
the Precambrian Eon 542 million years ago
11
Making Earths Continents

• Partial melting of basaltic
• rocks ? lower density
• continental crust
• D 2.7 g/cm3

2.7 g/cm3
3.0 g/cm3

• Partial melting of mantle ?
• basaltic rocks (ocean crust)
• D 3.0 g/cm3

5.5 g/cm3
Lithosphere
Continued Chemical Differentiation

• Formation of the lithosphere (thin crust)
• continental crust
• oceanic crust

Oldest Rocks

• Low density, low silica minerals
• move from the mantle toward
• surface lighter material rises

Acasta gneiss NW Canada 4.0 b.y.

• Formation of the Earths
• metallic core (Fe, Ni) and
• rocky mantle

12
Making Earths Continents

• Collision (convergence) and accretion of various
  island arc systems
• deformed and metamorphosed sediment
• shortening and thickening of continental crust
• silica-rich magmas (less dense) ascend and
  intrude rocks above
• continued accretion ? cratons
• modern-day exposed cratons are known as stable
  shields

The crust is on the move through plate tectonic
activity. Subduction of lithospheric material ?
numerous isolated island arc systems.
13
(No Transcript)
14
The Making of North America
Accretion of Crustal Provinces
oldest
youngest
youngest
oldest

• Piecemeal assembly into a continent
• Continued plate tectonic activity ? accretion of
  island arc systems known as
• crustal provinces
• About 1.9 billion years crustal provinces
  converged ? Trans-Hudson Mt. belt
• Other crustal provinces added over geologic time

15
I
the early earth .
3. Describe the atmospheric condition during
the Hadean Eon. 4. Describe the significance
of the banded iron formations. 5. Explain
how abundant concentrations of limestone
(CaCO3) were deposited during the
Precambrian Eon. 6. How would you describe a
craton?
16
Supercontinents of the Precambrian

• Supercontinent Cycle
• cyclic rifting and dispersal of one
  supercontinent followed by
• a long period of gradual reconstruction ? a
  new supercontinent

GONDWANA Between 800-600 m.y. fragments of
Rodinia become Gondwana (Southern Hemisphere)
Future Pangaea Continents that will
form Pangaea during the Phanerozoic Eon

• RODINIA
• Supercontinent
• dominating the
• Precambrian Eon
• Breaks apart by the
• end of the PC

17
Geologic History of the Phanerozoic Eon The
Formation of Earths Modern Continents
Phanerozoic encompasses approximately 542 million
years of geologic time.

• The Phanerozoic Eon
• Marks the appearance of first life forms
• Increased availability of fossils ? improved age
  accuracy
• Abundant organisms associated with various
  niches ?
• invaluable information to ancient environments

Phanerozoic Eon is divided into 3 main eras.
Cenozoic Era
65 m.y.
The Phanerozic Eon represents about 12 of the
geologic time scale
Mesozoic Era
186 m.y.
Paleozoic Era
291 m.y.
18
Evolution of the supercontinent Pangaea during
the Paleozoic
Laurasia Gondwana Pangaea
Laurasia
EQ

• Laurasia
• warm, wet tropical conditions
• abundant swampy conditions
• future coal deposits (Mississippian)

19
B
A
C
Pangaea

• The accretion of Pangaea resulted in
• collision of northern Europe with Greenland ?
  Caledonian Mountains-A
• joining of northern Asia (Siberia) and Europe ?
  Ural Mountains- B
• Joining of North Africa and Eastern U.S. ?
  Appalachian Mountains- C
• During the formation of the Appalachian
  Mountains, Pangaea was at
• its maximum size.

20
Mesozoic History 186 million years (Triassic,
Jurassic, Cretaceous)

• 
  Cretaceous Period
• Continued break-up of Pangaea ? forming the
  Atlantic Ocean
• Westward-moving North American plate converging
  with the Pacific
• basin
• Subduction of the Farallon plate (Pacific plate)
  producing
• coast ranges, Sierra Nevada Mts, Idaho
  batholith
• Laramide orogeny ? Formation of the Rocky
  Mountains

• 
  Jurassic Period
• Regressive / Transgressive seas deposit thick
  sequences
• of sedimentary rocks
• Colorado Plateau (Grand Canyon, Bryce Canyon)
  stratigraphy
• The Navajo Sandstone 300m thick (1000 feet)
• Middle Jurassic enormous desert
  (American-Southwest)
• evidenced by ancient sand dune remnants
• Steven Spielberg makes the movie Jurassic Park???

• Triassic Period
• Breakup of Pangaea ? modern day continents
• Much of the current continents above sea level
• evidenced by massive terrestrial sandstone,
  mudstone
• deposits

21
Massive cross-bedded sandstones deposited during
Middle Jurassic Period
22
I
The Paleozoic Era.
7. Distinguish between the following tectonic
landmasses (when they occurred
geologically) Rodinia, Gondwana, Laurasia,
Pangaea 8. How did the Appalachian Mountains
form? 9. Describe at least one significant
geologic event that has taken place during
the Triassic, Jurassic, and Cretaceous
periods.
23
Continent Configuration Cenozoic Era
24
Cenozoic History 65 million years (Tertiary,
Quaternary Periods)

• Cenozoic Era era of recent life
• Only a small amount of geologic time, but more
  is known about
• the Cenozoic than other eras (WHY?)
• rocks units widespread and less disturbed
• higher levels of fossil preservation

• Eastern North America (N.A.) during the Cenozoic
  Era
• Most of N.A. above sea level
• Eastern N.A. passive tectonic boundary
• tectonically stable considered a tectonic
  trailing edge
• erosional processes gt tectonic processes
• abundant marine deposition (transgression of
  seas) along the Gulf of Mexico ? numerous
  petroleum traps
• early Cenozoic --- Most of the Appalachian
  Mountains
• eroded ? the eastern seaboard

25
United States Geologic Map
Eastern United States Cenozoic geology
Western United States
passive tectonic margin trailing edge
Erosion of the Appalachians
Transgression of seas during the Cenozoic
26

• Western N.A. during the Cenozoic Era
• Laramide Orogeny ? the Rocky Mountains coming to
  an end.
• erosion of the Rocky Mountains ? sediments
  deposited
• (clastic-wedge), making the Great Plains
• Miocene Epoch (20 m.y. ago)
• Nevada into Mexico experienced crustal extension
  ?
• Basin and Province Range
• Faulted blocks (horst and grabens) extending
  from
• Nevada into Utah and portions of Mexico
• Rocky Mountains re-uplifted
• creating the Grand Canyon, Colorado
• creating the Grand Canyon, Snake River, Idaho
• Flood basalts in Oregon-Washington (CRBs)
• Flood basalts range in thickness up to 1 mile

27
United States Geologic Map
Western United States Cenozoic Geology
Flood Basalts CRB
Cascade Volcanoes
Larmide Orogeny ends Erosion of the Rocky
Mountains ? The Great Plains
Crustal Extension
Sierra Nevada batholith
Onset of the San Andreas Fault
28
I
the Cenozoic Era.
10. Describe at least 3 geologic events taking
place in Eastern U.S. and 3 geologic events
in Western U.S. 11. Why is the Eastern
section of the U.S. less tectonically
active than the Western U.S.? 12. What is
significant about the Laramide Orogeny?
29
(No Transcript)
30
The Geologic Time Scale and the association of
life will continue in the next section.