Ch. 22 - Earth's Evolution Through Geologic Time

Class: GEOL-101

Notes:

22.1 What Makes Earth Habitable?

List the principal characteristics that make Earth Habitable

Earth

Presentation content:

• Earth is the only planet in the solar system that can support life.
  • Liquid water
  • Oxygen-rich atmosphere
• Earth seems to be the right planet, in the right location, at the right time
• Earth is the right size.
  • Larger planets retain a thick, hostile atmosphere
  • Smaller planets have a thin or nonexistent atmosphere
• Earth has plate tectonics.
  • Formation of continental crust, highlands, and mountains
  • Without topography, would be covered with a shallow ocean
• Earth has a molten metallic core.
  • A magnetic field protects Earth from cosmetic rays that would strip away the atmosphere

Notes from the lecture:

• Negaunee Iron Formation (1.87 – 2.11 Ga) Negaunee, Michigan
  • Represent a time in the earths history when the atmosphere was developing, because of that we have development of these large iron formations
  • The Empire Mine (one of the largest Iron mines in the world)
• Larger planets -> thick atmospheres -> high temperatures
• If it wasn't for plate tectonics the earth would be flat
  • Think Interstellar Ocean planet with large tidal waves
• Magnetosphere protects us from solar radiation and protects the atmosphere from solar flares, it is a secondary layer that is essential
• Kepler planets (similar in size to Earth) are potential candidates

Right Location and Right Time

Presentation content:

• The Right Location
  • If Earth were 10 percent closer to the Sun
    • Too hot for liquid water
  • If Earth were 10 percent further from the Sun
    • Too cold for liquid water
  • The Sun is a modest-size star
    • Life span of 10 billion years
    • Larger stars burn out in a few million years
    • Sun’s life span allowed enough time for evolution
• The Right Time
  • Atmosphere
    • Earth’s early atmosphere lacked oxygen
    • Oxygen-rich atmosphere - 2.5 billion years ago
  • Mass extinction
    • 65 million years ago, an asteroid struck Earth
      • Opened new ecological-niche for mammals

Notes from the lecture:

• We are at this point in our geologic record where we have oxygen in the atmosphere, at some point there was some epoch where there was no oxygen.

22.2 Birth of a Planet

Outline the major stages in Earth’s evolution, from the Big Bang to the formation of our planet’s layered internal structure.

Birth of a Planet

Presentation content:

• The history of Earth began about 13.7 billion years ago with the Big Bang
• From the Big Bang to Heavy Elements
  • Hydrogen and helium formed shortly after the Big Bang
    • Clouds of these gases coalesced into stars
  • Heavier elements are formed in stars
    • Nuclear fusion occurs in the cores of stars
    • A supernova event occurs when a star explodes and creates the heaviest elements.
• The solar system formed from a solar nebula

Notes from the lecture:

• Earth was hit with a large impact at some point
• Earth started to cool down

Earth's Early Evolution

Presentation content:

• Repeated collisions with planetesimals and the decay of radioactive elements caused Earth’s temperature to increase
• Hadean eon
  • Iron and nickel melted and sank to form the metallic core, while less dense material rose to form the mantle and crust
  • Early Earth was covered in a magma ocean

Notes from the lecture:

• Early decay of these radioactive elements that have formed
• Cooling of earth -> density stratification of different elements

Earth’'s Primitive Atmosphere

Presentation content:

• Consisted mainly of hydrogen, helium, methane, ammonia, carbon dioxide, and water vapor
  • Hydrogen and helium escaped into space
  • Enhanced by volcanic outgassing
• No free oxygen in the early atmosphere

Notes from the lecture:

• Heavier elements stick around, thinks like Oxygen, methane, that started forming our early gases

Oxygen in the Atmosphere

Presentation content:

• Water vapor condensed into clouds and rain filled Earth’s oceans
• Approximately 3.5 billion years ago, photosynthesizing bacteria began to release oxygen into Earth’s oceans
• Initially, oxygen bonded with dissolved iron in the oceans
  • Formed Banded Iron Formations
• Eventually, oxygen began to build up in the atmosphere
  • The Great Oxygenation Event occurred 2.5 billion years ago
  • Allowed for the formation of ozone
    • Protected organisms from solar radiation
  • Excessive photosynthesis eventually led to the development of Snowball Earth

Notes from the lecture:

• There is not abundance of Oxygen in the atmosphere at this time
• Large global iron deposits started forming
  • Dominant source of Iron
• Great Oxygenation Event
  • Flip from a non-oxygen dominant environment to a dominant oxygen atmosphere
  • Started the development of our Ozone layer which protects organism from UV radiation
  • Lead to the dominance of bacteria at that time
  • During this time, because the oxygen became so abundant, we get the development of Snowball Earth
  • At that time, basically the earth underwind am extensive cooling event

22.3 Origin and Evolution of the Atmosphere

Describe how Earth’s atmosphere and oceans formed and evolved through time.

Evolution of the Oceans

Presentation content:

• (1) Earth cooled; (2) water vapor condensed; (3) rain fell; (4) water collected in low-lying areas
• Volcanic eruptions caused rainwater to be slightly acidic
  • Surface weathering rates increased
  • Products of chemical weathering increased salinity in the oceans
• Oceans are reservoirs for carbon dioxide
  • CO2 is locked up in limestone
  • Prevents a “runaway” greenhouse effect
    • Venus has an atmosphere composed of 97% CO2 that produced an extreme greenhouse effect, it’s surface temperature is 475ºC

Notes from the lecture:

• Some cyanobacteria that started the regulation of the temperature
  • Forms more and more limestone deposits
  • Excess of carbon dioxide to make limestone
  • Mediating our early greenhouse climate
• Sodium and potassium started to salinate the oceans
• Through that we have the ocean that we have today
• They always remain salty
• If we didn't have all of this, we would probably have an atmosphere similar to Venus

22.4 Precambrian History: The Formation of Earth's Continents

Explain the formation of continental crust, how continental crust becomes assembled into continents, and the role that the supercontinent cycle has
played in this process.

Precambrian

Presentation content:

• The Precambrian is divided into:
  • The Archean eon.
    • “Ancient Age”
  • The Proterozoic eon.
    • “Early Life”
  • Knowledge of this time is limited because much of the rock record has been destroyed.
• Making Precambrian Continental Crust
  • Silica-rich minerals were distilled from Earth’s mantle through partial melting.
  • Silica-rich materials buoyantly rise.
  • Crustal fragments formed at volcanic island arcs and hot spots.
  • By the end of the Archaean, 85% of modern continental crust had formed.

Notes from the lecture:

• Back from 4.6 to all the way to 4 billion years
• Earth being this gigant molten material that is cooling and gets stratification as it cools
  • Silica rich material that forms, rise.
  • We start to generate our early plate tectonics
  • Mixing all of these different magmas, that pushing pull model
• By the end of the Archean, 85% of the modern crust had formed

Earth's First Continents

Presentation content:

• From continental crust to continents
  • Crustal fragments collided and accreted to form larger masses
    • After multiple accretion events, eventually formed large crustal blocks called cratons.
    • A shield is a portion of a modern craton exposed at the surface.

Notes from the lecture:

• Cratons: the original continents
• Fused together with plate tectonics
• Some of these got squeezed together to form continents
  • Different types of rocks being squeezed together like playdoh

The Making of North America

Presentation content:

• Piecemeal assembly as a continent
  • Between 3.0 and 2.5 billion years ago
    • Accretion of numerous small crustal units
  • About 1.9 billion years ago
    • Collision of crustal provinces
  • During the Mesozoic and Cenozoic eras
    • Several terranes accreted onto the western margin of North America
      • North American Cordillera

Notes from the lecture:

• Collision of plates is generating younger material
• Different phases of plate tectonics that have allowed to grow to the present day configuration

Supercontinents of the Precambrian

Presentation content:

• Supercontinents are large landmasses that consist of all, or nearly all, existing continents.
  • Pangaea was the most recent
  • Rodinia preceded it. Formed about 1.1 billion years ago
    • Split apart 600–800 million years ago

Notes from the lecture:

• we know about this because we have wedges of different cratons stuck in other different plates
• We can have pieces of those different past plates in different continents

Supercontinent cycle

Presentation content:

• Supercontinent cycle
  • The supercontinent cycle is the splitting and reassembling of supercontinents.
  • Impacts Earth’s continents
  • Supercontinents, mountain building, and climate.
    • As continents move, ocean circulation patterns change, influencing climate
      • Example: Antarctic glaciation
    • Mountains created by the collision of continents change regional climate
      • Example: Sierra Nevada forests versus the Great Basin desert.
• Supercontinents and sea-level changes
  • High rate of seafloor spreading
    • Warm oceanic crust displaces seawater causing sea level to rise
  • Low rate of seafloor spreading
    • Cool oceanic crust sits lower in the ocean basin causing sea level to fall

Notes from the lecture:

• Think of the move "The day after tomorrow"
  • Everything freezing
• Reconfiguration events has a big role in our climate
• If we had this super continent right at the equator, what would happen?
  • You would actually start to cool because you have difference in reflectivity
  • A lot more vegetation would grow
  • Probably more CO2 under the soil, etc.
• Can also correlate to extinction events
• Also displaces sea water over the continents
  • Or you expose more land

22.5 Geologic History of the Phanerozoic: The Formation of Earth’s Modern Continents

List and discuss the major geologic events in the Paleozoic, Mesozoic, and Cenozoic eras.

Phanerozoic encompasses 542 million years

Presentation content:

• Divided into:

  • Paleozoic Era
  • Mesozoic Era
  • Cenozoic Era.

• Phanerozoic is marked by the appearance of life-forms with hard parts.

  • Shells, scales, bones, or teeth.

Notes from the lecture:

• Paleozoic - started to see organism with shells
  • From simple cyanobacteria to more complex organisms

Paleozoic History

Presentation content:

• At the start of the Paleozoic, North America was a barren lowland
  • Periodically, shallow seas invaded the continents resulting in deposition of limestone, shale, and sandstone
• Formation of Pangaea
  • Laurasia was the vast northern continent.
    • Composed of North America, Europe, Siberia, and smaller crustal fragments
    • Tropical landmass that led to the formation of swamps which converted to coal
  • Gondwana was the vast southern continent.
    • Composed of South America, Africa, Australia, Antarctica, and India

Notes from the lecture:

• Paleozoic can be defined in terms of the development of Pangaea

Formation of Pangaea

Presentation content:

• Gondwana migrated northward and collided with Laurasia to form Pangaea.
  • Accretion lasted 300 million years and formed several mountain belts
    • Formed the Caledonian, the Appalachian, and the Ural Mountains
• Pangaea reached its maximum size 250 million years ago.

Notes from the lecture:

• By 250 m years ago that Accretion event had basically ended.

Mesozoic History

Presentation content:

• Mesozoic History
  Changes in sea levels
  • Early in the Mesozoic much of the land was above sea level
  • By the middle Mesozoic, seas invaded western North America
  • Coal formation in western North America
  • By the late Mesozoic, shallow seas encroached on much of
  western North America
  • Led to the formation of “coal swamps”
  • Cretaceous coal deposits are economically important
  • Breakup of Pangaea
  • 185 million years ago, a rift developed between North America and
  Africa
  • Marked the start of the Atlantic Ocean
  • Westward-moving North Atlantic plate began to override the Pacific
  plate
  • Resulted in a wave of deformation along the western margin of
  North America

Notes from the lecture:

• During that time North America was all basically flooded

Formation of the North American Cordillera

Presentation content:

• Subduction of the Farallon plate led to 100 million years of volcanic activity
  • Granitic plutons of the Sierra Nevada, Idaho batholith, and British Columbia’s Coast Range Batholith
• Subduction of the Farallon plate also led to the piecemeal addition of crustal fragments
  • Exotic terranes
• Late Mesozoic Laramide Orogeny led to the development of the Rocky Mountains

Notes from the lecture:

• North America is now colliding with the Farallon plate
• Large scale volcanism, large scale mountain building event
• Responsible for the development of the Rocky Mountains

Cenozoic History

Presentation content:

• Cenozoic History
  • Represents a considerably smaller fraction of geologic time compared to the Mesozoic and Paleozoic eras
    • More is known about this era because the rock formations are more prevalent and widespread
• Eastern North America
  • Stable continental margin
    • Abundant marine sedimentation
      • Most extensive development around the Gulf of Mexico
  • Appalachians eroded to a low plain
    • Isostatic adjustment raised the region and rejuvenated its rivers

Notes from the lecture:

• Pretty short compared to other periods
• Seeing weather and erosion
• Mexico was basically filled in with sediments over time

Western North America

Presentation content:

• Laramide Orogeny was coming to an end
  • Erosional forces lowered the Rocky Mountains and filled basins with sediment
    • Large wedge of sediment created the Great Plains
• 20 million years ago, broad region from Nevada to Mexicoa experienced crustal extension
  • Created fault-block mountains and formed the Basin and Range Province
• Entire western interior uplifted
  • Re-elevated the Rocky Mountains and rejuvenated many western rivers
    • Many spectacular gorges, such as the Grand Canyon, were created
• Volcanic activity was common
  • Basaltic plateaus formed in Washington, Oregon, and Idaho
• Last 2.6 million years dominated by glacial/interglacial cycles

Notes from the lecture:

• Pressing a soccer ball, it flattens, and when we let go it goes back to being round
• US started sliding westward?
• Mountains formed through the continent being squeezed and then letting it go (remove that pressure) repeatedly
• Western US is till undergoing active volcanism

22.6 Earth's First Life

Describe some of the hypotheses on the origin of life and the characteristics of early prokaryotes, eukaryotes, and multicellular organisms.

The Oldest Fossils

Presentation content:

• The oldest fossils are 3.5 billion years old
  • Similar to cyanobacteria
  • Chemical traces suggest life may have existed 3.8 billion years ago

Notes from the lecture:

• Important because that allowed for the evolution of the earth's early atmosphere
• Isotopic signatures that reflect the existance of organism, but not evidence (fossils)

Origin of Life

Presentation content:

• Amino acids are essential molecules for proteins

• Many hypotheses for the formation of amino acids

  • Synthesized from ultraviolet light.
  • Synthesized from a lightning strike.
  • Brought to Earth from asteroids.
  • Developed in hydrothermal vents or hot springs.

• Earth’s first life: prokaryotes

  • First known organisms were single-celled bacteria, prokaryotes, which lacked a nucleus.
    • Early prokaryotes were anaerobic; Later prokaryotes were photosynthetic

• Evolution of eukaryotes (cells contain a nucleus)

  • Eukaryote are more advanced - all plants and animals are eukaryotes
  • Multicelled organisms did not evolve until 1.2 billion years ago
    • First primitive marine animals did not evolve until 600 million years ago

Notes from the lecture:

• You can actually create amino acids with an experiment
• The first signs of microbial life emerged around 3.5 billion years ago. Scientists think early life may have formed from lightning strikes or arisen in deep sea vents.
• Eukaryotes appeared after the oxygenation event
• Stromatolites are among the most common Precambrian fossils
  • Live in an environment where no other organism can live, very high temperature environments

22.7 Paleozoic Era: Life Explodes

List the major developments in the history of life during the Paleozoic era.

Paleozoic

Presentation content:

• The Paleozoic starts with the Cambrian Period
  • Spectacular variety of life-forms
    • All major invertebrate groups first appear in the Cambrian.
    • Expansion in biodiversity is coined the Cambrian Explosion.
• Early Paleozoic Life-Forms
  • The Cambrian period was the golden age of trilobites
  • The Ordovician period marked the appearance of abundant cephalopods (Highly developed mollusks)
  • Early diversification driven by the emergence of predators

Notes from the lecture:

• Hominoids: predominant fossils
• Cephalopods:
  • Giant squids / octopus

Early Paleozoic Life-Forms

Presentation content:

• Early Paleozoic Life-Forms
  • First land plants evolved 400 million years ago
    • Evolved to adapt to living on land.
    • Many difficulties to overcome:
      • Obtaining water.
      • Staying upright against gravity and winds.

Notes from the lecture:

• First vascular plant moving on the land
• Mississippian period: dense extensive forests
  • Timeframe these began to be fossilized
  • 400-300 M years ago
  • Early insects evolving
  • Still not many organisms living on Earth
  • First amphibians

Vertebrates Move to Land

Presentation content:

• Lobe-finned fishes adapted to land and became the first amphibians
  • Used fins to move from one pond to another.
• Amphibians are not fully adapted to life out of the water
  • Born in the water with gills and a tail.
  • Air-breathing adults with legs.

Notes from the lecture:

• Diversification of early reptiles
  • Reptiles: Laid eggs on land
  • Amphibian: laid eggs on water

Reptiles: The First True Terrestrial Vertebrates

Presentation content:

• Reptiles were better adapted to live on land
  • “waterproof” skin
  • Shell-covered eggs
    • These “private aquariums” eliminate the need to reproduce in the water

Notes from the lecture:

• Do not worry about keeping their eggs actually wet
• Long organisms start to dominate
• Amphibians relatively state the same through geologic time
• Fish is the same, more or less stay the same but huge diversification of species

The Great Permian Extinction

Presentation content:

• The most significant mass extinction over the past 500 million years.
  • 70% of land-dwelling species went extinct.
  • 96% of marine organisms went extinct.
• Ultimately created more diverse biological communities
• Several causes:
  • Volcanic activity
  • Asteroid impact

Notes from the lecture:

• We cannot really determined what actually caused these extinction events
• Because of this extinction event, it opened a lot of space for other organisms to become dominant.

22.8 Mesozoic Era: Dinosaurs Dominate the Land

Summarize the major developments in the history of life during the Mesozoic era.

Gymnosperms: The Dominant Mesozoic Trees

Presentation content:

• Gymnosperms (cycads, conifers, and ginkgoes) became the dominant trees of the Mesozoic.
  • Did not need freestanding water for fertilization
• Fossil gymnosperms in Arizona’s Petrified National Park.

Notes from the lecture:

• There were no flowering plants
  • Very limited vegetation but huge huge trees
  • Moving from high temperature weather to more lower

Reptiles Dominate the Land, Sea, and Sky

Presentation content:

• First reptiles were small, but they evolved rapidly
  • Dinosaurs evolved into large and small organisms, herbivorous and carnivorous organisms.
  • Pterosaurs had membranous wings that allowed for rudimentary flight.
  • Ancestors to modern birds (like Archaeopteryx) had feathered wings and reptilian characteristics.
  • Other reptiles returned to the sea.
• Reptiles were the dominant terrestrial organism in the Mesozoic
  • Many went extinct at the end of the Mesozoic.

Notes from the lecture:

• Massive dominant dinosaurs (Jurassic World water dinosaur type)
• A lot of evolution going on
• Ancestors of birds
  • A lot of them are flightless, have reptilian features but have feathers

Extinction

Presentation content:

• What could have triggered the extinction of one of the most successful groups of land animals?
• Researchers suggest a “one–two punch”
  • Climate data indicates that average temperature increased by more than 20ºC
  • Coincided with massive basaltic eruptions that produced the Deccan Plateau
  • 66 million years ago our planet was struck by a stony meteorite
  • Evidence in the form of sediment containing a high level of the element iridium, rare in Earth’s crust but found in high proportions in stony meteorites.

Notes from the lecture:

• We know there was a meteorite impact at that time but we also know that there was large volcanic activity throughout the world during that time as well
• Rotational temperature fluctuation
  • +-20 degrees
• We can derive that from the KT boundary -> increases in radioactivity
  • You can have these little tiny layers that represents the sedimentary boundary of the cretaceous extinction boundary

22. 9 Cenozoic Era: Mammals Diversity

Summarize the major developments in the history of life during the Mesozoic era.

Mammals and plants

Presentation content:

• In the Cenozoic, mammals replaced the reptiles as the dominant land animals
• Angiosperms (flowering plants with seeds) replaced gymnosperms as the dominant plants
  • Strongly influenced the evolution of birds and mammals

Notes from the lecture:

• With he extinction event all these dominant organisms were not abel to survive but mammals and birds they were able to survive, migratory and move around.
• Lead to Angiosperms appearing

From Reptiles to Mammals

Presentation content:

• Earliest mammals coexisted with dinosaurs in the Mesozoic.
  • Small, nocturnal, rodent-like creatures.
• Mammals are distinct from reptiles.
  • Give birth to live young.
  • Have mammary glands.
  • Warm-blooded
    • Can occupy more diverse habitats than cold-blooded creatures.
• Cenozoic mammals diversified rapidly.

Notes from the lecture:

• Mammals were very small before, by the time of the Cenozoic they receive a massive evolution timeframe and diversification, they become the dominant organisms during that time
• Can occupy more diverse habitats, higher latitude and regions, different environmental conditions

Humans: Mammals with Large Brains and Bipedal Locomotion

Presentation content:

• Several populations of anthropoids diverged 7 or 8 million years ago in Africa.
  • One line produced modern apes, one line produced several varieties of human ancestors.
  • Good fossil evidence in sedimentary basins in Africa.
  • Australopithecus shows skeletal characteristics of both apelike ancestors and modern humans.
    • Upright posture and bipedal locomotion.
    • Correlates with leaving forest habitat and moving to open grasslands.
  • Many species of the genus Homo.
    • Examples: Homo habilis and Homo erectus.
    • Homo sapiens originated in Africa 200,000 years ago.

Notes from the lecture:

• Footprints of Australopithecus in ash deposits at Laetoli, Tanzania
• Exploring a large climate change
• Mammals started to migrate
• Homo sapiens: early humans evolving

Large Mammal Extinction

Presentation content:

• Many mammals diversified into very large organisms.
  • Examples: 5-meter-tall hornless rhinoceros, mastodons, mammoths.
• Most large mammals went extinct in the Pleistocene.
  • Climate fluctuations?
  • Early humans?
  • Diseases?

Notes from the lecture:

• At that time, homo sapiens were not the dominant organism
  • Large mammals were dominant: mammuts, mastodons
• But we had this ability to learn so we were able to survive for a long time
• Higher latitudes were covered in ice during that time
• Sea levels were lowere
• Early humans were able to migrate through paths that were inaccessible because of ice
  • Lead to more diseases
• We still have elephants, they were able to survive
• Over hunting hypothesis
  • Why didn't we wipe out things like elephants or lions?
  • This questions it.
  • If climate fluctuated too much, while do some organisms remained and others not so much?

End of Chapter 22 - Concept Checks

22.1 What Makes Earth Habitable?

1. Explain why Earth is just the right size to support life.
2. In what way does Earth’s molten, metallic core help protect Earth’s life-forms?
3. Why is Earth’s location in the solar system ideal for the development of complex life-forms such as humans?

22.2 Birth of a Planet

1. What two elements made up most of the observable matter in the very early universe?
2. What is the name for a cataclysmic event in which an exploding massive star produces heavy elements?
3. Briefly describe the formation of the planets from the solar nebula.

22.3 Origin and Evolution of the Atmosphere and Oceans

1. List the major gases that were added to Earth’s early atmosphere through the process of outgassing.
2. Why was the evolution of photosynthesizing cyanobacteria important for the evolution of large, oxygen-consuming organisms such as humans?
3. How does the ocean remove carbon dioxide from Earth’s atmosphere? What role do tiny marine organisms, such as foraminifera, play in the removal of carbon dioxide?

22.4 Precambrian History: The Formation of Earth’s Continents

1. Describe how cratons came into being.
2. What is the supercontinent cycle? What supercontinent preceded Pangaea?
3. Explain how the rate of seafloor spreading is related to changes in sea level.

22.5 Geologic History of the Phanerozoic: The Formation of Earth’s Modern Continents

1. During which period of geologic history did the supercontinent Pangaea come into existence?
2. Compare and contrast eastern and western North America’s geology during the Cenozoic era.

22.6 Earth’s First Life

1. What group of organic compounds combine to form proteins and is therefore necessary for life as we know it?
2. What are stromatolites?
3. Compare prokaryotes with eukaryotes. To which group do most modern multicellular organisms belong?

22.7 Paleozoic Era: Life Explodes

1. What is the Cambrian explosion?
2. Describe the obstacles plants had to overcome in order to inhabit the continents.
3. What group of animals is thought to have moved onto land to become the first amphibians?
4. What major developments allowed reptiles to move inland?

22.8 Mesozoic Era: Dinosaurs Dominate the Land

1. What group of plants became the dominant trees during the Mesozoic era? Name a modern descendant of this group.
2. What was the dominant reptile group on land during the Mesozoic?
3. What group of reptiles gave rise to modern birds?

22.9 Cenozoic Era: Mammals Diversify

1. Explain how the demise of the dinosaurs impacted the development of mammals.
2. Where did researchers discover most of the evidence for the early evolution of our hominin ancestors?
3. What two characteristics best separate humans from other mammals?