Phanerozoic (541-0 Ma): Complex Life and Mass Extinctions

Question 1

what does fossil preservation favour?

Answer 1

hard parts (shells, bones)

Question 2

what are the types of Body Fossils?

Answer 2

(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

Question 3

how can soft parts be preserved?

Answer 3

(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

Question 4

what exceptional conditions does preservation of soft parts require?

Answer 4

Rapid burial by sediment

Anoxic conditions

Question 5

what is the significance of the Cambrian period?

Answer 5

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”

Question 6

what was the distribution of landmasses like in the Cambrian?

Answer 6

Warm tropical seas, wide continental shelves

Question 7

what life evolved in the Devonian period?

Answer 7

Corals, sponges, insects

massive land plants -> high O2 -> alter landscape evolution, weathering

Question 8

what happened in the early paleozoic?

Answer 8

Life flourished

Carboniferous – reptiles, winged insects– swamp forests (-> coal)

Question 9

what were the main paleozoic events?

Answer 9

“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

Question 10

what happened in the permian (300-252 Ma)>

Answer 10

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

Question 11

what happened in the end permian extinction (250 Ma)?

Answer 11

Loss of 95% of all marine species, 70% of land species

Greatest ever extinction

Question 12

what are some speculated causes of the Permian Extinction?

Answer 12

(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

Question 13

what were the main mesozoic events?

Answer 13

first dinosaurs, Pangaea begins to break up
early mammals
first birds, placental mammals, flowering plants
extinction of dinosaurs, ammonites etc.

Question 14

what did the break up of pangea lead to?

Answer 14

Changes in ocean circulation

Continental aridity reduced -> global warming

Question 15

what was terrestrial plant life like in the mesozoic?

Answer 15

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

Question 16

what was marine life like in the mesozoic?

Answer 16

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

Question 17

what was the climate like in the cretaceous?

Answer 17

High sea level
Global warming
High ocean crust production
Long period of NO magnetic reversals
Connection between events in mantle, core and surface?

Question 18

what species were affected by the cretaceous/tertiary (K/T) extinction (66 Ma)?

Answer 18

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

Question 19

what is a possible volcanic cause for the K-T extinction?

Answer 19

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

Question 20

what is the Alvarez hypothesis?

Answer 20

a giant asteroid impact ended dinosaurs

Question 21

what is the evidence for the Alvarez hypothesis?

Answer 21

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

Question 22

what would be the effect of a large asteroid impact?

Answer 22

Vaporisation of asteroid and impacted rocks
Tsunami (from impact into water)
Dust in atmosphere -> global darkness
Wildfires
No photosynthesis -> Biological crisis!

Question 23

how big would the asteroid have to be for the Alvarez hypothesis?

Answer 23

Asteroid ~10 km diameter
Crater ~ 150-200 km wide
~200 million times more energy released than largest thermonuclear bomb ever tested

Question 24

where is the crater from the Alvarez hypothesis?

Answer 24

Chicxulub, Yucatan Peninsula
Known from 1950’s vintage oil exploration
Right age, right size (~180 km)

Question 25

what was the cause of the K/T extinction?

Answer 25

volcanism and an asteroid impact both likely contributed

Question 26

what was the climate like in the early cenzoic?

Answer 26

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)

Question 27

what has happened during the Holocene (the last 12,000 years)?

Answer 27

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

Question 28

when have mammoths been extinct since?

Answer 28

around 4 Ka

Question 29

when have quaggas been extinct since?

Answer 29

1883

Question 30

when have dodos been extinct since?

Answer 30

1662

Question 31

what are some characteristics of the ‘anthropocene’?

Answer 31

Human impact
Resource extraction
Sustainability
Energy