Week 11 Flashcards
1
Q
The Phanerozoic Eon (PreCambrian)
A
- All time before Cambrian time
- Divided into 3 Eon’s
- Hadean (Beggining to 4000 Mya)
- Archean (4000 - 2500 Mya)
- Proterozoic (2500 - 541 Mya)
2
Q
The Great Oxygenation Event (Oxygen Catastrophe)
A
- Known as First Extinction (2400 Mya)
- Until 2.5Gyr ago, the atmosphere was rich in volcanic volatiles (especially carbon dioxide)
- Mostly soft bodied, meaning no fossils and no evidence
3
Q
Snowball Earth Hypothesis
A
- Multiple waves of glaciation, rather than one cooling event, 850 – 630 Mya
- Cold conditions were conducive to greater biodiversity!
4
Q
End-Ediacaran Mass Extinction (End-Precambrian)
A
- End of the Proterozoic (~541Myr ago) devastating loss of life among the soft-bodied
- The main culprit: Ocean Anoxia, choking life rooted to the seafloor
- Little evidence remains today – many still argue no extinction occurred because fossilized forms are rare
- Following the extinction of nearly all the life on Earth, we lead into the Cambrian Explosion (Lots of room for new species)
5
Q
The Cambrian Period
A
- 542 - 488 Mya (During Rodinia)
- Life still marine, land barren
- Sea level rose and life flourished
- Sparks Cambrian Explosion (new species)
6
Q
The Cambrian Extinctions
A
- Competition within the environment forced many to extinction
- With increasing speciation, the background extinction rate was increasing as well
- Two distinct extinctions occur during the Cambrian Period: the Dresbachian and the Botomanian – each accounting for the death of 40% of marine genera
- Both events are likely driven by global cooling and glaciation, which lead to lowering sea levels and the closing of enteric seas
7
Q
The Ordovician Period
A
- 488 – 461 Myr ago
- Intense volcanism and overall greenhouse conditions
-Tropical waters were likely ~45°C, with many shallow enteric seas produced as a result of high water-levels - As continents began colliding to form Gondwana, vast volcanic belts formed releasing immense volumes of volcanic voltatiles
- As Gondwana drifted south, it developed glaciers which quelled much of the volcanism, lowering CO2 production and reducing the Greenhouse Effect
8
Q
The Ordovician Extinction(s)
A
- With climate going up and down chaotically, life was able to flourish
- Loss of 85% of all species (second only to the End-Permian)
- Extinction was likely driven by a sudden period of glaciation between 447 – 444 Myr ago
- Huge land mass (Gondwana!) was centred over the South Pole, massive expansive ice sheets formed
- Ice sheets sucks immense volumes of water from the oceans, lowering sea-levels to their lowest ever
- Just as the ice would recede and life would return, glaciation would advance again and kill species again!
- Then, temperatures warmed and sea levels rose again – no more major glaciations again until the Carboniferous!
9
Q
The Silurian Period
A
Span: 444 – 416 Myr ago
- Gondwana was still holding on to a couple glaciers at the South Pole
- Sea Levels were moderately high, with many enteric seas
- Little volcanism to drive Greenhouse conditions, but enough to sustain warmth
- Increasing biodiversity in the oceans
- Movement of life onto land, still a few million years away
10
Q
The Devonian Period
A
- Span: 416 – 359 Myr ago
- Intense period in terms of tectonism, biodiversity, climate and mass extinctions
- Land masses were beginning to converge, with larger continents such as Laurentia forming and Gondwana growing
- Fairly moderate climate, with few glaciers present
- This was called “The Age of Fish” for the influx in biodiversity
- Some fish developed strong enough lungs to crawl out of the oceans and onto land!
- First Terrestrial forests, developing seeds and 8m tall
11
Q
The Devonian Period Extinctions
A
- 370 – 360 Myr ago,
- Loss of 80-85% of all marine species by the end of the Devonian
- At ~370 Myr ago, the geologic record shows black shales, with three closely-spaced layers featuring tektites, shocked quartz, tsunami, and Iridium – all indications for a Meteor Impact!
- Few craters are dated to the extinction, with the Siljan Ring (diam.=52km) in Sweden matching temporally and geologically
12
Q
The Late Devonian Extinctions
A
- Extinctions around 360 Myr ago, blame can be placed on the terrestrial plants colonizing land
- These plant nutrients washed into the oceans, massive rapid growths of algae
- Algae died, decomposition used incredible amounts of O2 and replaced it with huge volumes of CO2
- Multiple waves caused massive losses in the Devonian Oceans
- Period spanning 360 – 345 Myr ago, no fossils are preserved, “Romer’s Gap”,
13
Q
The Carboniferous Period
A
- 359-299 Myr ago,
- Break from the Greenhouse conditions of the previous periods
- Period of rapid glaciation, indication of an Icehouse climate
- Massive ice sheets on Gondwana over the south pole caused sea level to drop
- Pangea started to form
- Shallow seas formed from colliding continents
- This proliferation of life in the shallow tropical wetlands prevented a global extinction from sea level drop
14
Q
Life in The Carboniferous Period
A
- Started with warm climate
- Temperature later dropped, leading to very rapid ice sheet building on Gondwana especially
- Even as climate cooled, the tropical latitudes stayed warm and moist – perfect for the huge Psaronius to grow
- These ‘fern-trees’ sat submerged in ~1m swampwater, and grew to 10-15m high
- The vast number of Psaronius growing across the globe, upon dying and deposition in muddy bogs, have produced the largest coal deposits ever made
15
Q
The Permian Period
A
- 299-251 Mya
- Continents (finally) arranged into Pangaea
- Shallow seas had either closed or dried up
- The change in terrestrial climate forced a change in trees growing – Conifers and their seed-cones first developed in the Permian interior!
- Oceans were strong biodiversity and life seemed to be doing great!
- Many new reptiles branched off the Carboniferous amphibians, producing the ancestors to most dinosaur species
