Earths Evolution Through Geologic Time Why is Earth

Earth’s Evolution Through Geologic Time

Why is Earth Unique? • Life is ubiquitous! – It’s 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 • External forces vs. Internal forces So, how did earth become what it is today?

65 my 186 my 88% of Geologic Time 251 my 291 my 542 my 4600 my

I The Geologic Time Scale. 1. 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

Start of the Precambrian 4. 6 by • explosion from a single point • universe expanding • cooling • more contraction / accretion planetesimals Earth Primitive atmosphere starts to form during the Hadean Eon H, He • contraction • fusion begins prtosun chemical differentiation • contribution of heavy elements

The Hadean Eon (4. 6 b. y. ): “hellish” conditions As the Earth begins to cool… In Earth’s early formation: • atmosphere: H, He, CH 4, NH 3, CO 2, H 2 Ovapor • weak gravity H, He is lost to space • T-Tauri phase (high solar winds) removed all the other gasses Earth’s First Enduring Atmosphere: • produced by outgassing – gasses escape from the Earth’s interior • outgassing produced by hundreds of active volcanoes • Earth was in a “fluid state, ” releasing high amts of gas • Earth’s atmosphere from outgassing • water vapor, CO 2, SO 2, minor amounts of other gasses So, where is the oxygen?

Oxygen in the Earth’s Atmosphere • Increasing oxygen-generating organisms • oxygen increased steadily to stable concentrations • “the oxygen explosion” forms ozone (O 3) • formed in the stratosphere • protects life (DNA) from UV radiation • Oxygen reacts with iron, creating banded iron formations (3. 5 – 2 b. y. ago) • iron + oxygen --> RUST • alternating layers of chert and iron-rich rocks • Photosynthesizing bacteria release oxygen into the water---- 3. 5 billion years ago • CO 2 + H 2 O + Energy sun --> Oxygen • A cooling earth Condensing water vapor (clouds) and rain, producing the oceans (filling in low areas) Stable O 2 levels by 1. 5 b. y. Banded Iron Formations Cynobacteria (blue-green algae) 4. 0 b. y.

Banded Iron Formations • Deposited during the Precambrian Eon • 3. 5 to 2 billion years ago

Evolution of the Earth’s Oceans CO 2 (major greenhouse gas) readily soluble in seawater (the oceans) CO 2 + H 2 O + Ca+2 Ca. CO 3 (Limestone) Atmospheric CO 2 Organisms extract Dissolved ions Ca. CO 3 shells and die in the ocean producing LS-sediment Earth’s atmosphere rich in H 2 S , CO 2, SO 2 • • • Rain + H 2 S, CO 2, and SO 2 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. )

White Cliffs of Dover, England Thick chalk sequence (Ca. CO 3) deposited during the Precambrian Eon – 542 million years ago

Making Earth’s Continents • Partial melting of basaltic rocks lower density continental crust D= 2. 7 g/cm 3 3. 0 g/cm 3 5. 5 g/cm 3 Lithosphere • Partial melting of mantle basaltic rocks (ocean crust) D = 3. 0 g/cm 3 Continued Chemical Differentiation • Formation of the lithosphere (thin crust) • continental crust • oceanic crust • Low density, low silica minerals move from the mantle toward surface – lighter material rises • Formation of the Earth’s metallic core (Fe, Ni) and rocky mantle Oldest Rocks Acasta gneiss NW Canada 4. 0 b. y.

Making Earth’s 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.

The Making of North America “Accretion of Crustal Provinces” oldest 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

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 (Ca. CO 3) were deposited during the Precambrian Eon. 6. How would you describe a craton?

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

Geologic History of the Phanerozoic Eon The Formation of Earth’s 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. 65+ m. y. Cenozoic Era 186 m. y. Mesozoic Era 291 m. y. Paleozoic Era The Phanerozic Eon represents about 12% of the geologic time scale

Evolution of the supercontinent Pangaea during the Paleozoic Laurasia + Gondwana = Pangaea a i s a ur La EQ Laurasia • warm, wet tropical conditions • abundant swampy conditions • future coal deposits (Mississippian)

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.

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 – 300 m 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

Massive cross-bedded sandstones deposited during Middle Jurassic Period

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.

Continent Configuration Cenozoic Era

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 > 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

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

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 (CRB’s) • Flood basalts range in thickness up to 1 mile • Continued convergence producing the Cascade Volcanoes • subduction of the Farallon plate stratacomposite volcanoes • Sierra Nevada batholith, Idaho batholith faulted and uplifted • Mesozoic batholiths exposed to the surface • The onset of the San Andreas Fault • A portion of California (North American Plate) begins to “slide” northwest against the Pacific plate.

United States Geologic Map Western United States Cenozoic Geology Flo od Ba CRB salts Cascade Volcanoes Larmide Orogeny ends Erosion of the Rocky Mountains The Great Plains Crustal Extension Sierra Nevada batholith Onset of the San Andreas Fault

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?