Lecture Outlines Natural Disasters, 5th edition

1
The Great DyingsNatural Disasters, 6th edition,
Chapter 16
2
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
  extinctions
• Knowledge comes through fossil record

3
Fossils

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

Figure 16.6
4
Fossils

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

5
Early Understanding of Extinctions and Geologic
Time

• 1786, French paleontologist Georges Cuvier
  proved that extinction of species had occurred
• Skeletons of mammoths demonstrably different that
  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

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Early Understanding of Extinctions and Geologic
Time

• William Smith, 1799 law of faunal assemblages
• Strata of same age can be recognized by same
  fossils
• 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
  1815

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Early Understanding of Extinctions and Geologic
Time

• First geologic maps led to global movement in
  geology
• 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

8
Early Understanding of Extinctions and Geologic
Time

• 20th century geologic column refined with
  absolute ages from radioactive dating ? geologic
  timescale

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Early Understanding of Extinctions and Geologic
Time

• 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

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Early Understanding of Extinctions and Geologic
Time

• 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
  fossils
• Evolution, increasing diversity and extinctions
  continue

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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
  species
• 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
  modification)

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Species and the Fossil Record

• Extinction caused by inability to adapt to
  changes in physical, chemical, biological
  conditions
• Background level of extinctions always
  occurring
• Present species diversity 40 to 80 million
  species
• 0.1 of species that have existed in Earth
  history
• 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

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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,
  etc.
• Periods of Earth history with and without reefs
• Each time reefs reappeared, built by different
  organisms

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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

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Mass Extinctions During Phanerozoic Time

• Extinction-frequency curve number of extinctions
  plotted against recurrence interval ? estimates
  of how often given size extinction might occur

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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

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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

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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

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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
  interiors
• Numerous habitat changes
• Large, combined landmass ? fewer number of
  species
• Smaller, isolated landmasses ? larger number of
  species

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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

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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
  lava

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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, causing greenhouse effect, warming
  climate
• Eruption of Ontong Java plateau may have raised
  global temperatures up to 13oC

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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
  effect
• Global climate changes

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Possible Causes of Mass Extinctions

• Ocean Composition Causes
• Ocean is chemically connected to dissolved salts,
  bottom sediments, continents, atmosphere
• Equilibrium maintained by negative feedback
  buffers,
• 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
  circulation
• 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

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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

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Possible Causes of Mass Extinctions

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

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Possible Causes of Mass Extinctions

• Biologic Causes
• Species-Area Effects
• Smaller area ? fewer species

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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
  boundary)

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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 few species to extinction
• Extinction of numerous species around world
  probably requires two or more causes

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Examples of Mass Extinctions

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

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Examples of Mass Extinctions

• Closing of Permian Time (Ended 253 Million Years
  Ago)
• Climate Changes
• Supercontinent ? less shoreline ? greater
  percentage of land away from climate-moderating
  effects of ocean
• Drier, more severe climate in interior of
  landmass
• 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
  organisms
• Turnover of stratified layers may kill surface
  organisms

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Examples of Mass Extinctions

• Closing of Permian Time (Ended 253 Million Years
  Ago)
• 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
  rain
• 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

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Examples of Mass Extinctions

• Closing of Permian Time (Ended 253 Million Years
  Ago)
• 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

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Examples of Mass Extinctions

• Close of Cretaceous Time (Ended 65 Million Years
  Ago)
• 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
  terminated
• Over 35 of genera and 65 of species went extinct

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Examples of Mass Extinctions

• Close of Cretaceous Time (Ended 65 Million Years
  Ago)
• Sea Level Fall
• During final 18 million years of Cretaceous,
  global sea levels went from high to low, climate
  cooled
• 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

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Examples of Mass Extinctions

• Close of Cretaceous Time (Ended 65 Million Years
  Ago)
• 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
  km/sec
• Fireball with 2,000 km diameter
• Searing hot winds ignite wildfires throughout
  North America
• Earthquake with magnitude greater than 11

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Examples of Mass Extinctions

• Close of Cretaceous Time (Ended 65 Million Years
  Ago)
• 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
  organisms
• Dust blocked sunlight ? stopped photosynthesis
  for months
• Greenhouse gases remained aloft, raised
  temperatures
• Mass extinctions led to opportunities for
  surviving organisms (including mammals)

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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

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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

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Quaternary Extinctions

• Arguments against climate change as cause
• More large-animal extinctions than plant
  extinctions
• Large mammals not affected by climate change
• Increase in habitable land from retreat of
  glaciers should cause increase in species, not
  decline
• 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

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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

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Quaternary Extinctions
43
Quaternary Extinctions
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In Greater Depth La Brea Tar Pits, Metropolitan
Los Angeles

• One of most spectacular fossil localities in
  world
• Oil from underground reservoirs seeped upward to
  surface where natural gas and lighter-weight oils
  evaporated, leaving sticky, high-viscosity tar in
  pools
• Over last 40,000 years, more than 660 species of
  organisms trapped and entombed (59 mammal
  species)
• Escape very difficult for four-legged, heavy
  animal
• 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

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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
  (Mexico)
• Horses and camels, which originated in North
  America
• Elephants to replace mammoths, mastodons,
  gomphotheres
• 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

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End of Chapter 16