Phanerozoic (541-0 Ma): Complex Life and Mass Extinctions Flashcards
what does fossil preservation favour?
hard parts (shells, bones)
what are the types of Body Fossils?
(1) Hard parts unaltered e.g. vertebrate bones, shells
(2) Hard parts replaced e.g. shells replaced with pyrite or other minerals; petrified wood
(3) Molds: impressions/imprints of organisms; and
Casts: sediment that fills the mold, taking the organism’s shape
how can soft parts be preserved?
(1) Unaltered body fossils e.g. insects in amber, tar pits
(2) Carbonisation e.g. plants, Burgess Shale organisms preserved as carbon films (loss of volatiles)
(3) Trace Fossils e.g. footprints, trails
what exceptional conditions does preservation of soft parts require?
Rapid burial by sediment
Anoxic conditions
what is the significance of the Cambrian period?
The oldest undoubted fossil occurrences of each of the major groups of animals living now
Likely that all major animal groups originated in the Cambrian (even those that left no known fossils) -> the “Cambrian Explosion”
what was the distribution of landmasses like in the Cambrian?
Warm tropical seas, wide continental shelves
what life evolved in the Devonian period?
Corals, sponges, insects
massive land plants -> high O2 -> alter landscape evolution, weathering
what happened in the early paleozoic?
Life flourished
Carboniferous – reptiles, winged insects– swamp forests (-> coal)
what were the main paleozoic events?
“Cambrian explosion” - animals with skeletons, 541 Ma
first vertebrates, around 485 Ma
first land plants
first jawed fish
first insects, seed plants, land vertebrates
first reptiles, winged insects
largest mass extinction, 252 Ma
what happened in the permian (300-252 Ma)>
Return to supercontinent status (Pangea)
Pangea aligned north/south
Extreme conditions; arid climate on continents
Party over? End Permian marked by largest ever mass extinction
what happened in the end permian extinction (250 Ma)?
Loss of 95% of all marine species, 70% of land species
Greatest ever extinction
what are some speculated causes of the Permian Extinction?
(1) Glaciation global widespread cooling &/or low sea level (2) Formation of supercontinent Pangea: -> reduced shallow continental shelves -> ecological competition for space (3) Volcanic Eruptions massive basaltic lava eruptions in Siberia -> ash, sulfates, F, Cl into atmosphere -> global cooling
what were the main mesozoic events?
first dinosaurs, Pangaea begins to break up
early mammals
first birds, placental mammals, flowering plants
extinction of dinosaurs, ammonites etc.
what did the break up of pangea lead to?
Changes in ocean circulation
Continental aridity reduced -> global warming
what was terrestrial plant life like in the mesozoic?
Triassic: Gymnosperms (conifers) supplant seed ferns
- tough on herbivores (ferns more palatable; conifers: spiny, toxic leaves, slow growing)
Cretaceous: Change to flowering plants
- attract insects
- fruit, nuts for seed dispersal
- small weeds, then trees: e.g. magnolia, holly, oak, walnut
- support herbivores: dinosaurs
what was marine life like in the mesozoic?
Development of Modern Fauna:
- Phytoplankton: Coccolithophores - algae
- Zooplankton: foraminifera -> feed on phytoplankton
- molluscs, ammonites, swimming predators
- gastropods (snails), bivalves, modern corals
- fish (ray-finned bony fish)
- marine reptiles: marine lizards, sea turtle
what was the climate like in the cretaceous?
High sea level Global warming High ocean crust production Long period of NO magnetic reversals Connection between events in mantle, core and surface?
what species were affected by the cretaceous/tertiary (K/T) extinction (66 Ma)?
Loss of 75%+ of all species Ended age of the dinosaurs Complete demise of: - Dinosaurs, pterosaurs, belemnoids - Many species of plants (except among ferns & seed-producing plants) - Ammonites, marine reptiles, rudist bivalves Severely affected: - Planktonic forams, calcareous nanoplankton, diatoms, dinoflagellates - Brachiopods, molluscs, echinoids, fish Primarily unaffected: - Most mammals, birds, lizards, snakes - Most turtles, crocodiles, amphibians
what is a possible volcanic cause for the K-T extinction?
Deccan Traps
Massive lava flows at 66 Ma, Deccan Plateau, west-central India
Multiple layers of flood basalt, total > 2 km thick, cover 500,000 km
what is the Alvarez hypothesis?
a giant asteroid impact ended dinosaurs
what is the evidence for the Alvarez hypothesis?
Analysed clay layer at K-T boundary in limestones in Italy, specifically for the element iridium
Iridium: rare element (dense), common in meteorites
Discovered high Iridium content in the clay layer at K-T boundary
-> asteroid impact
-> debris thrown into atmosphere and distributed worldwide
what would be the effect of a large asteroid impact?
Vaporisation of asteroid and impacted rocks Tsunami (from impact into water) Dust in atmosphere -> global darkness Wildfires No photosynthesis -> Biological crisis!
how big would the asteroid have to be for the Alvarez hypothesis?
Asteroid ~10 km diameter
Crater ~ 150-200 km wide
~200 million times more energy released than largest thermonuclear bomb ever tested
where is the crater from the Alvarez hypothesis?
Chicxulub, Yucatan Peninsula
Known from 1950’s vintage oil exploration
Right age, right size (~180 km)
what was the cause of the K/T extinction?
volcanism and an asteroid impact both likely contributed
what was the climate like in the early cenzoic?
Warming followed by cooling
India approaching Asia– continental collision since ~50 Ma
-> uplift (Himalayan Mts)
-> weathering (uses up CO2)
-> cooling
Gap widened between S. America & Antarctica
-> Antarctic Circumpolar Current
-> Isolated southern ocean from warmer Pacific, Atlantic, Indian Oceans
-> Glaciers on Antarctica (Oligocene, 35 Ma)
what has happened during the Holocene (the last 12,000 years)?
Holocene epoch (since last glaciation): geologically brief Humans began ~2 Ma, & have evolved into significant agent of extinction Destruction of every 200 km2 of tropical forest and 100,000 km2 of rangeland results in loss of 1 species (50% in next 100 years?) Deforestation, agricultural practices, pollution, overhunting, and numerous other human activities -> numerous species threatened
when have mammoths been extinct since?
around 4 Ka
when have quaggas been extinct since?
1883
when have dodos been extinct since?
1662
what are some characteristics of the ‘anthropocene’?
Human impact
Resource extraction
Sustainability
Energy
