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Lecture Outlines Natural Disasters, 7 th edition

Lecture Outlines Natural Disasters, 7 th edition. Patrick L. Abbott. The Great Dyings Natural Disasters, 7 th edition, Chapter 16. The Great Dyings. Massive human loss by natural disasters is insignificant when compared to great dyings in fossil record

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Lecture Outlines Natural Disasters, 7 th edition

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

  2. The Great DyingsNatural Disasters, 7th edition, Chapter 16

  3. 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

  4. Fossils • Evidence of former life • Requisites for fossilization: • Possession of hard parts –shells, bones, teeth • Rapid burial, protecting from scavenging or disintegration • Dinosaursknown by fossil bones, teeth and footprints • Abundantfootprintsshow that some species lived inherds Figure 16.5 Figure 16.6

  5. Fossils 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 miner’s body preserved for 2,300 years in salt mine collapse Figure 16.8

  6. Early Understanding of Extinctions and Geologic Time • 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 • Steno’s 1669 law of superposition: • Younger layers of sediment are deposited on top of older layers Figure 16.10

  7. 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

  8. 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

  9. Early Understanding of Extinctions and Geologic Time • 20th century: geologic column refined with absolute ages from radioactive dating  geologic timescale Figure 16.11

  10. 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

  11. 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 Figure 16.12

  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 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)

  13. 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

  14. 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 Figure 16.15

  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

  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

  17. Possible Causes of Mass Extinctions Plate Tectonic Causes • Today: oceans cover ~71% of Earth’s surface, continents~29% • Sea level drop: continents could cover up to 40% • Sea level rise: continents could cover only 17% Figure 16.19

  18. 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

  19. 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

  20. Possible Causes of Mass Extinctions Numbers and Sizes of Continents • Late Permian to early Triassic (260 – 240 million years ago): supercontinentPangaea • 200 million years ago: Pangaea began to be rifted apart into today’s continents • Greatly lengthened world’s 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

  21. 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

  22. 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

  23. 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 climate • Eruption of Ontong Java plateau may have raised global temperatures up to 13oC

  24. 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 • Earth’s heat balance changes via greenhouse effect • Global climate changes

  25. 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

  26. 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

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

  28. Possible Causes of Mass Extinctions Biologic Causes • Species-Area Effects • Smaller area  fewer species Figure 16.24

  29. 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) Figure 16.25

  30. 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 requirestwo or more causes

  31. 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

  32. 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

  33. 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

  34. 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

  35. 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

  36. 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

  37. 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

  38. 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)

  39. 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

  40. 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

  41. 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

  42. 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

  43. Quaternary Extinctions Figure 16.31

  44. Quaternary Extinctions

  45. 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

  46. 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

  47. End of Chapter 16

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