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Title: Lecture Outlines Natural Disasters, 7th edition

Lecture OutlinesNatural Disasters, 7th edition
  • Patrick L. Abbott

The Great DyingsNatural Disasters, 7th edition,
Chapter 16
The Great Dyings
  • Massive human loss by natural disasters is
    insignificant when compared to great dyings in
    fossil record
  • Entire species, millions of entire species ? mass
  • Knowledge comes through fossil record

  • Evidence of former life
  • Requisites for fossilization
  • Possession of hard parts shells, bones, teeth
  • Rapid burial, protecting from scavenging or
  • Dinosaurs known by fossil bones, teeth and
  • Abundant footprints show that some species lived
    in herds

Figure 16.5
Figure 16.6
  • Examples
  • Fossilized tree sap ? amber
  • Burial in oxygen-poor swamps or peat bogs
    preserves organisms, like tanning
  • Frozen animals (like mammoths) exposed as
    glaciers melt
  • Celtic miners body preserved for 2,300 years in
    salt mine collapse

Figure 16.8
Early Understanding of Extinctions and Geologic
  • 1786, French paleontologist Georges Cuvier
    proved that extinction of species had occurred
  • Skeletons of mammoths demonstrably different from
    skeletons of elephants ? mammoths had gone extinct
  • Observed profound changes in sedimentary record
  • Abrupt first appearances of fossils
  • Abundant fossils in overlying layers
  • Absence in higher overlying layers
  • Stenos 1669 law of superposition
  • Younger layers of sediment are deposited on top
    of older layers

Figure 16.10
Early Understanding of Extinctions and Geologic
  • William Smith, 1799 law of faunal assemblages
  • Strata of same age can be recognized by same
  • Law of superposition law of faunal assemblage ?
    law of faunal succession
  • Fossils from older (lower) rock layers are older
    and more different from present-day organisms
    than fossils from younger (higher) rock layers ?
    old forms of life have died out and new forms of
    life have developed
  • Geologic maps of England and Wales published in

Early Understanding of Extinctions and Geologic
  • First geologic maps led to global movement in
  • Sedimentary strata from around world classified
    and subdivided on basis of fossil assemblages
  • Same fossils found in rocks in different areas ?
    same age rocks
  • 1841 standard geologic column based on fossil
    succession, relative ages

Early Understanding of Extinctions and Geologic
  • 20th century geologic column refined with
    absolute ages from radioactive dating ? geologic

Figure 16.11
Early Understanding of Extinctions and Geologic
  • Brief History of Life
  • 3.85 billion years ago archaea
  • Found today at mid-ocean ridges, killed by oxygen
  • Three branches of life archaea, bacteria,
    eukarya (plants, animals)
  • 3.5 billion year ago photosynthetic bacteria
    removing CO2 from atmosphere, adding O2
  • 1 billion years ago single cell division ?
    sexual reproduction
  • 620 million years ago multicellular animal life

Early Understanding of Extinctions and Geologic
  • Brief History of Life
  • 543 million years ago life began
    40-million-year-long burst of evolutionary change
  • First hard parts (shells, etc.) that preserve as
  • Evolution, increasing diversity and extinctions

Figure 16.12
Species and the Fossil Record
  • Swedish botanist Linnaeus laid out basic
    terminology of divisions of life into kingdoms
    down to species
  • Species
  • Population of organisms so similar in life habits
    and functions that they can breed together and
    produce reproductively viable offspring
  • Reproductively isolated by differences from other
  • Share common pool of genetic material (genome)
  • May migrate over broad area ? mutation of genes
    may cause reproductive isolation between local
    populations ? evolution (Darwin descent with

Species and the Fossil Record
  • Extinction caused by inability to adapt to
    changes in physical, chemical, biological
  • Background level of extinctions always
  • Present species diversity 40 to 80 million
  • 0.1 of species that have existed in Earth
  • 99.9 of species that have existed in Earth
    history are extinct
  • Extinctions clear out niches ? opportunity for
    new organisms to evolve to occupy habitats
  • Mass extinctions open up many new niches ? burst
    of evolution

The Tropical Reef Example
  • Reefs porous, wave-resistant frameworks built by
    organisms such as corals, clams, etc., and used
    by organisms such as red algae, worms, bryozoa,
  • Periods of Earth history with and without reefs
  • Each time reefs reappeared, built by different

Figure 16.15
Mass Extinctions During Phanerozoic Time
  • Average life span of species 4 million years
  • Plot extinctions of genera (above species)
    against time
  • extinction number of generic extinctions
  • number of genera alive at that time
  • Background extinctions have declined from about
    50 in Cambrian time to about 5-10 recently
  • Spikes in extinctions ? mass extinctions

Figure 16.16
Mass Extinctions During Phanerozoic Time
  • Extinction-frequency curve number of extinctions
    plotted against recurrence interval ? estimates
    of how often given size extinction might occur

Figure 16.17
Figure 16.18
Possible Causes of Mass Extinctions
  • Plate Tectonic Causes
  • Today oceans cover 71 of Earths surface,
    continents 29
  • Sea level drop continents could cover up to 40
  • Sea level rise continents could cover only 17

Figure 16.19
Possible Causes of Mass Extinctions
  • Changes in Seafloor Spreading Rates
  • More rapid spreading ? spreading ridges increase
    in mass, volume ? sea level rises
  • Mid-Cretaceous (110 to 85 million years ago)
    faster seafloor spreading ? global sea level 200
    m higher than today
  • Double area of shallow seas ? warmer climate
  • Severely reduced area of exposed land

Figure 16.21
Figure 16.20
Possible Causes of Mass Extinctions
  • Sea-Level Changes
  • Bigger glaciers ? lower sea level
  • Most recent expansion of glaciers (20,000 years
    ago) sea level 140 m lower than today
  • If all glaciers melted sea level 70 m higher
    than today
  • Sea level also rises or falls by changes in
    seafloor spreading rates can combine with each
    other or cancel each other out

Figure 16.22
Possible Causes of Mass Extinctions
  • Numbers and Sizes of Continents
  • Late Permian to early Triassic (260 240 million
    years ago) supercontinent Pangaea
  • 200 million years ago Pangaea began to be rifted
    apart into todays continents
  • Greatly lengthened worlds shorelines
  • Reduced areas of climatically harsh continental
  • Numerous habitat changes
  • Large, combined landmass ? fewer number of
  • Smaller, isolated landmasses ? larger number of

Possible Causes of Mass Extinctions
  • Continental Position and Glaciation
  • Large landmasses at poles necessary to capture
    enough snow to create massive ice sheets that
    cause Ice Age
  • Ice Age climatic extremes of glacial advances
    and retreats ? stresses on species ? extinctions

Possible Causes of Mass Extinctions
  • Volcanic Causes
  • Flood basalt immense volumes of basaltic lava
    erupted in geologically short time period,
    covering millions of square kilometers of Earth
  • Ontong Java flood basalt plateau created 120
    million years ago
  • 36 million km3 of lava erupted in less than 3
    million years
  • World sea level rose 10 m as ocean displaced by

Possible Causes of Mass Extinctions
  • Changes in Atmospheric Composition
  • Flood basalt eruption ? emission of massive
    volume of gases
  • Sub-sea eruptions oceans absorb and dilute some
    gas, ocean-water acidity and oxygen
    concentrations change
  • Continental eruptions gas goes directly into
    atmosphere, enhancing greenhouse effect, warming
  • Eruption of Ontong Java plateau may have raised
    global temperatures up to 13oC

Possible Causes of Mass Extinctions
  • Climate Change Causes
  • Climate change complex network of positive and
    negative feedback responses
  • Volcanism
  • Emits tremendous volume of gases
  • Composition of atmosphere changes
  • Earths heat balance changes via greenhouse
  • Global climate changes

Possible Causes of Mass Extinctions
  • Ocean Composition Causes
  • Ocean is chemically connected to dissolved salts,
    bottom sediments, continents, atmosphere
  • Equilibrium maintained by negative feedback
  • Occasionally overcome ? lethal disequilbrium
  • Today oceans stirred by currents between
    different density layers
  • Deep waters well oxygenated, rich with life
  • Warm climate intervals inadequate ocean
  • Polar waters too warm to sink
  • Organic decay at ocean bottoms used up oxygen ?
    anoxic waters caused sea life extinctions
  • Melting of glaciers flooded surfaces of oceans
    with fresh water ? lethal to sea life species

Possible Causes of Mass Extinctions
  • Extraterrestrial Causes
  • When 10 km diameter object hits Earth
  • Wildfires, acid rain, tsunami, dust cloud ? weeks
    of dark winter, gases ? greenhouse effect
    temperature rise

Figure 16.23
Possible Causes of Mass Extinctions
  • Extraterrestrial Causes
  • Bombardment of cosmic rays increases if supernova
  • Bombardment of subatomic particles from Sun
    increases when Suns intensity changes
  • Both increase during periods of weakened magnetic
  • (No correlation to fossil record found)

Possible Causes of Mass Extinctions
  • Biologic Causes
  • Species-Area Effects
  • Smaller area ? fewer species

Figure 16.24
Possible Causes of Mass Extinctions
  • Biologic Causes
  • Random Extinction
  • Number of individuals of species goes up and down
    randomly (random walk)
  • Randomness guarantees that number of individuals
    will eventually hit zero ? no recovery (absorbing

Figure 16.25
Possible Causes of Mass Extinctions
  • Biologic Causes
  • Predation and Epidemic Disease
  • Excessive predation can drive number of
    individuals of species low enough for random
    extinction to finish the job
  • Large carnivores or epidemic disease
  • Today homo sapiens biggest predator
  • Multiple Causes of Mass Extinction
  • Any one factor alone can cause local stress to
    drive a few species to extinction
  • Extinction of numerous species around world
    probably requires two or more causes

Examples of Mass Extinctions
  • Closing of Permian Time (Ended 253 Million Years
  • On land ¼ amphibian orders, 1/50 reptile genera
  • Oceans 80 or more species went extinct
  • Formation of Supercontinent Pangaea
  • Uniting of continents into supercontinent closed
    equatorial sea ? reduced shallow seas ? triggered
  • Sea-Level Fall
  • Slower seafloor spreading shrank mid-ocean
    ridges, lowering sea level 200 m
  • Reduced area of shallow seas ? triggered

Examples of Mass Extinctions
  • Closing of Permian Time (Ended 253 Million Years
  • Climate Changes
  • Supercontinent ? less shoreline ? greater
    percentage of land away from climate-moderating
    effects of ocean
  • Drier, more severe climate in interior of
  • Ocean Composition Changes
  • End of long Ice Age disappearance of cold polar
    waters may have slowed ocean circulation and led
    to anoxic bottom water, killing deep-water
  • Turnover of stratified layers may kill surface

Examples of Mass Extinctions
  • Closing of Permian Time (Ended 253 Million Years
  • Siberian Traps Flood Basalt
  • 3 million km3 of lava erupted within 1 million
    years, emitted huge volume of gases (CO2)
  • Heated permafrost to release water vapor, methane
    from hydrates
  • Greenhouse gases raised global temperatures, acid
  • Duration of the Extinction Events
  • Took less than 1 million years
  • Change in carbon isotopes (from collapse in
    biological productivity) in maybe less than
    30,000 years

Examples of Mass Extinctions
  • Closing of Permian Time (Ended 253 Million Years
  • Life at the End of Permian Time
  • Tropical seas virtually eliminated
  • One major landmass placed species-area effect
    pressure on terrestrial life
  • Land covered in desert
  • Deep-ocean water became anoxic, CO2-rich
  • Climate warmed
  • Extinction of Permian species allowed Mesozoic
    reptiles (dinosaurs) to take over

Examples of Mass Extinctions
  • Close of Cretaceous Time (Ended 65 Million Years
  • Late Cretaceous North American heartland covered
    with herds of dinosaurs and flowering plants
  • Slow-acting changes elevated background level of
    extinctions, followed by deadly volcanism and
    asteroid impact slow decline abruptly
  • Over 35 of genera and 65 of species went extinct

Examples of Mass Extinctions
  • Close of Cretaceous Time (Ended 65 Million Years
  • Sea Level Fall
  • During final 18 million years of Cretaceous,
    global sea levels went from high to low, climate
  • Deccan Traps Flood Basalt
  • Deccan Sanskrit for southern, trap Dutch for
    staircase thick piles of basaltic rock
  • Over 2 million km3 erupted in less than 1 million
    years, beginning 65.5 million years ago
  • Worldwide climatic effects, like Permian Siberian
    traps flood basalt

Examples of Mass Extinctions
  • Close of Cretaceous Time (Ended 65 Million Years
  • Chicxulub Impact
  • Yucatan peninsula, Mexico rings (180 km, 300 km
    diameter) of shattered rock ? asteroid impact 65
    million years ago
  • Worst-case scenario
  • 10 km asteroid plunges through atmosphere at 10
  • Fireball with 2,000 km diameter
  • Searing hot winds ignite wildfires throughout
    North America
  • Earthquake with magnitude greater than 11

Examples of Mass Extinctions
  • Close of Cretaceous Time (Ended 65 Million Years
  • Chicxulub Impact
  • Worst-case scenario
  • Tsunami 2 to 3 km high
  • Blasted hole up to 60 km deep, shot plume of
    vaporized water and rock into stratosphere
  • Acid rain (from vaporized rock) killed ocean
  • Dust blocked sunlight ? stopped photosynthesis
    for months
  • Greenhouse gases remained aloft, raised
  • Mass extinctions led to opportunities for
    surviving organisms (including mammals)

Living Fossils
  • Not all species went extinct at Permian/Triassic
    and Cretaceous/Tertiary mass extinctions
  • Horseshoe crabs have survived for last 450
    million years
  • Sharks have been successful predators for last
    350 million years biggest threat of extinction
    is today, from humans
  • Conifers, ferns, horsetail and scouring rushes
    have existed since 275 million years ago
  • Norfolk pine, gingko biloba, metasequoia, and
    sago palm have existed since 235 million years ago

Living Fossils
  • Quaternary Extinctions
  • Significant extinctions of large-bodied mammals
    in last 1.5 million years, during glacial
    advances and retreats
  • Concentrations of extinctions ? multiple causes
  • Suspected additional cause of many extinctions ?
    Homo sapiens
  • Large animals decimated in Americas and Australia
  • Large animals fared best in Africa where humans
    evolved co-existed for thousands of generations
  • Wherever humans went, extinctions followed

Quaternary Extinctions
  • Arguments against climate change as cause
  • More large-animal extinctions than plant
  • Large mammals not affected by climate change
  • Increase in habitable land from retreat of
    glaciers should cause increase in species, not
  • No equivalent extinctions earlier during present
    Ice Age
  • Australia
  • Humans arriving in Australia 56,000 years ago
    found 24 genera of large-bodied animals ? 1,000
    years later, 23 of those were extinct
  • Regional, not global event ? not climate-caused

Quaternary Extinctions
  • Madagascar and New Zealand
  • When humans arrived, largest animals were
    flightless birds elephant birds in Madagascar
    and moas in New Zealand
  • Humans killed birds and stole eggs until
    populations were low enough that random
    extinction finished them off
  • Rate of human-induced or related extinctions
    increased in last 12,000 years, increased even
    more in last 200 years

Quaternary Extinctions
Figure 16.31
Quaternary Extinctions
In Greater Depth La Brea Tar Pits, Metropolitan
Los Angeles
  • One of most spectacular fossil localities in
  • Oil from underground reservoirs seeped upward to
    surface where natural gas and lighter-weight oils
    evaporated, leaving sticky, high-viscosity tar in
  • Over last 40,000 years, more than 660 species of
    organisms trapped and entombed (59 mammal
  • Escape very difficult for four-legged, heavy
  • Distress cries brought carnivores and scavengers
    ? 85 of larger-bodied victims
  • Also one 9,000 year old partial human skeleton
    indicates human presence during extinctions

Side Note The Rewilding of North America
  • North America lost many large-bodied vertebrate
    species around 13,000 years ago
  • Plan to restore large populations of vertebrates
    with similar species from elsewhere
  • Critically endangered 50 kg Bolson tortoise
  • Horses and camels, which originated in North
  • Elephants to replace mammoths, mastodons,
  • In fenced reserves cheetahs, lions
  • Pros ties in with bison and wolf ranges
    underway, undo human harm, save species from
    extinction, enhance biodiversity and evolutionary
    potential, ecotourism
  • Cons not genetically identical to extinct
    species, habitats have changed, possible disease
    transmission, unexpected consequences

End of Chapter 16
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