The Palaeozoic Flashcards
What eon is the Palaeozoic in? What other eras are also in this eon?
Phanerozoic eon is divided into three eras:
• Palaeozoic (543 to 250 million years ago), divided into six periods
• Mesozoic (250 to 65 million years ago), divided into three periods
• Cenozoic (65 million years ago to present), divided into two periods and seven epochs
Determining climate without high resolution proxies:
Polar = Tillites, striations Temperate = coal, fossil trees with rings Deserts = evaporites, sand dunes Tropical = shallow marine limestones, coal, fossil trees with no rings
Late Proterozoic
650 mya)
• Rodinia slowly breaks apart (supercontinent split)
Cambrian
- Sudden appearance in the fossil record of many new phyla (Cambrian explosion)
- Fauna included:
- Earliest animals with a notochord (Pikaia gracilens)
- Abundant marine invertebrates
- Brachiopods
- Arthropods
- Echinoderms
- Algae
- Gradual or sudden?
- Generally warm and humid
- High seas levels
- Few continental landmasses located at the poles
- Ocean currents were able to circulate freely
- No significant ice formation
Cambrian – generally warm and humid – clashes with snowball earth theory
When was the Ordovician?
Ordovician (488 to 443 my BP)
Early Ordovician
• Still high sea levels
• Gondwana still at low latitudes, but drifting south
• Sedimentary rock dominated by deposition of carbonates
• Little continental erosion, very flat continents
• Early Ordovician quite warm
• First terrestrial land plants (liverworts)
• Mychorrizal fungi
Early Ordovician climate typical of a warm, ‘greenhouse’ state
mycorrhizal fungi
• mycorrhizal fungi help transport of P from soil to roots
• increases soil area from which P can effectively be accessed by roots
• mycorrhizae also enhance P uptake by releasing phosphatase
• mycorrhizae can release organic acids which accelerate weathering of minerals
Accelerates plant growth by being a stabilizing species – make the environment less hostile
Late Ordovician
- Gondwana reaches south pole
- Glaciation
- Preceded by drop in atmospheric CO2: from ~7000 to ~4000 ppm
- Sea level dropped due to water being locked up in ice sheets
- Glaciation at 440 my BP lasts around 1 million years
- Sea level drop was massive due to shallow nature of seas at the time
- Horizontal drop in sea level was huge due to continental shelves becoming land
- Organisms died with elimination of ecological niches
- 2nd largest extinction event in Earth history (60% of marine species)
- *high co2 for glaciation – could be an error
Silurian
(443 to 416 my BP)
• Gondwana still high south latitudes
• Panthalassa Ocean covered most of the northern hemisphere
• Caledonian orogeny begins (Baltica and northern Avalonia)
• Glaciation, but less pronounced than during Late Ordovician
• Glaciers largely retreated by Middle
• High sea level
• Stabilisation of climate
• First appearance of jawed fish
• First appearance of vascular plants
• Cooksonia
• Plants with cells specialized for the conduction of fluids such as water and sap. This includes all existing plants except for mosses and liverworts
• Vascular plants = means beginning of terrestrial vegetation as we know it
Devonian General
(416 to 359 Ma BP)
• Laurentia and Baltica collide to form a supercontinent in Early Devonian
• Gondwana still in the southern hemisphere
• High sea levels – lots of sedimentary rock found around world
• Much of land submerged under shallow seas
• Increased organic matter input into streams (more black shale deposition
• Organic deposition in oceans becomes more consistent
• Decrease surface albedo by 10-15%
• Devonian was the terrestrial equivalent
• of the ‘Cambrian Explosion’
Devonian Trees
- Oldest fossil forest known is the Gilboa forest (Mid-Devonian)
- Developed in an over bank deposit
- Now found in New York state
- Cladoxylopsida - Genus Wattieza –
- oldest tree
- Spectacular fossil discovered in 2005
- Full trunk and base of leaves
- Palm-like
- Deep roots increased rates of pedogenesis - breaking up rock and creating soil
- Webbed leaves resulted in shade
- Shade resulted in cooling
- Created entirely new biome – the forest
From plants to trees:
- Eventually leads to need for roots for increased water uptake and stability
- More roots = holding riverbanks together = leads to meanders = slower rivers
- Deeper roots – more stable sources of groundwater – larger plants reinforced with lignin in xylem = trees
- Also begin to grow higher to release spore and compete for water
- Leads to tree evolution
- Devonian forests = first source of coal -
- Oxygen concentrations skyrocket – once it reached 13% in atmosphere fire was possible (by lightning strikes)
- Turned plants to charcoal – extra detail of plants preserved from the mid-Silurian onwards – follow the development of xylem and stomata through time
Devonian Mass Extinction
• One of ‘big five’
• Particularly severe for benthic marine organisms that lived in shallow tropical seas (warm water)
• Many of the taxa that survived the extinctions were typically deep-water or high- latitude relatives of the decimated forms
• The impact on terrestrial plants fairly minimal
“The Devonian Plant Hypothesis”
• First proposed by Thomas Algeo, Robert Berner, J. Barry Manard, and Stephen Scheckler in 1995
• Increased erosion from continents caused eutrophication of oceans
• Increased silicate weathering caused glaciation, and important changes in the oceans by dropping sea level
Similar causality as Ordovician mass extinction (Gondwana glaciation)
- Recent research finds a large mercury spike in sediment from transition
- Argues that large-scale volcanic centres affected climate
- Either cooling or warming
- Argues further that all ‘big five’ extinctions are now linked with volcanism
Carboniferous
(359 to 299 Ma BP)
• Sea level increases from Devonian
• Warm early Carboniferous
• Still evidence of ice on Gondwana, increasing through the Carboniferous
• Coal swamps at low latitudes
• Land masses begin to rejoin – forming Pangaea
Beginning of massive ice age (Permo-Carboniferous)
• Land plants included Lepidodendron and Sigillaria
• Amphibians and spiders appear
• Lots of insects (800 types of cockroach)
• Very high oxygen meant insect ‘gigantism’
- Sequestering of organic carbon reached a Phanerozoic peak during this time
- Land plants continued to spread
- Tropical coal had no growth rings (no seasonality)
- Mid-latitude coal has growth rings (seasonality)
- First conifers
- Main source of modern-day coal
How do we know that carbon was sequestered?
• Cyclothems – Peat growing in coastal swamps – Periodically inundated – Pressure turns peat to coal – Oxygen isotopes • Carbon isotopes • Cycles of rock units being deposits - relates to malankovich cycles Oxygen isotopes: Lower at ice age because 18O is in ice, not in ocean Carbon Isotopes:
Standard is usually the Peedee belemnite (limestone) from South Carolina – this is referred to as per mil PDB (% PDB)
Lots of carbon 13 in rocks when carbon 12 is low and has been taken up by plants which break it down easier than carbon 13
Interprets as there being lots of O2 during this period due to photosynthesis
Organisms preferentially incorporate light C
High 12Corg burial rates result in high 13C/12C in seawater and CaCO3
Permian
(299 to 251 Ma BP)
• Major transition in vegetation from ferns to more advanced conifers and ginkgo trees
• Deserts were established
• Insects continued to radiate, with the appearance of Coleoptera (beetles) and Diptera (flies)
• Reptiles thrived and began their radiation
• Largest mass extinction on record occurred at end: 96% of animal species disappeared
