S3: W11 (Prof. Kelsey) Flashcards
Dispersal-Vicariance attributes? (5)
• Before plate tectonics was accepted, dispersal was the only mechanism that could be used to explain many distributions.
• Darwin’s Ho was LJD.
• Vicariance biogeographers: “Dispersal can be invoked to explain any distributio. It cannot be tested & is not science”.
• Vicariance biogeographers were WRONG! because dispersal does happen and it can be tested.
• Vicariance is often the most parsimonious explanation. If so, it is the best & simplest explanation.
Hypotheses we consider in Dispersal-Vicariance? (2)
• Dispersal hypothesis.
• Vicariance hypothesis.
Dispersal hypothesis?
= depends on the biology of organisms (do you know/are you provided with the biology of the organism?).
Vicariance hypothesis?
= often the simplest explanation as it simply says that a mountain popped up & separated populations, resulting in their divergence (for example).
Eg of Dispersal-Vicariance?
Panama isthmus.
Explain Panama isthmus? (3)
● Species pairs across the isthmus (key to species vicariance).
● Pattern repeated in shrimp, fish, snails.
● Vicariance in that isthmus rose up out of ocean, divided those populations & those populations started to diverge.
Dispersal-Vicariance vs Secular migration?
● Secular migration
= species divergence due to adaptation.
● Dispersal-Vicariance
= species divergence due to separation/barrier.
Thing to note about Panama isthmus eg?
Species pairs give you an idea of what causes divergence.
Eg of Dispersal hypothesis/Dispersal?
Juncus.
Eg of Vicariance hypothesis/Vicariance?
Northofagus.
Explain eg of Juncus? (5)
● Wind-blown in roaring 40s.
● Little genetic structure.
● No common community links (no coupling of organisms).
● Volcanic islands & continents.
● Good eg of LJD.
Explain eg of Nothofagus? (5)
● Seeds don’t survive in sea water.
● Strong genetic structure (high Fst).
● Community structure exists.
● Continental landmasses only.
● Phylogenetic relationships.
Goelogical Time Scales (GTS) attributes? (6)
• Hierarchical (eons, eras, periods & epochs).
• Transitions among the geological strata & the associated fossils.
• Names are based on sediments exposed during that time.
• Length of time.is different.
• Time scale is non-linear so you have to think about whether it is logarithmic or shortened.
• Defining a time point is based on biodiversity & change in geology.
What is defining a time point based on? (2)
• Biodiversity during that time.
• Change in geology (chemical composition– Ur to Pb).
Geology attributes? (2)
• ½ life of difference elements help you figure out the dates of time.
• Correlate to biodiversity by indicating a shift in biodiversity.
Plate tectonics attributes? (6)
• Original name was Continental drift.
• Most profound & important impact on the study of biogeography.
• How they are situated on the Earth informs decisions on species diversity & distribution.
• Highly speculative idea in the early 1900s to a well-established fact in the 1960s.
• Continents have rafted across the surface of the Earth on the upper mantle of the Earth’s crust.
• Today, it is conclusive.
Why is Plate tectonics conclusive today? (2)
It’s because of:
• Evidence (direct & indirect).
• We know more about the mechanisms.
Wegener’s continental drift attributes? (6)
• German meteorologist.
• Remarkable insights & formulated intuitive ideas around plate tectonics.
• Noted the alignment of the continents across the Atlantic & realized many things.
• Wegener’s ideas were met with huge resistance.
• Most evidence only came to light decades after he died.
• Made many insightful hypotheses.
What are the “things” that Wegener realized? (5)
● Coal beds in N. America & Europe indicate a more tropical climate in the past.
● The tillites in subtropical Afriac indicated a much cooler climate at one time.
● Tillites in Africa & S. America are continuous with each other.
● Many biogeographic patterns are more easily explained if continents had been joined.
● In these times, the continental shelf had not been mapped.
Tillite?
= lithified till that is evidence of much older glaciation.
What were Wegener’s insightful hypotheses? (10)
● Continental rocks (sial) are less dense, thicker & less magnetized than those of the ocean floor (which is composed largely of basaltic rock & is collectively called sima).
● Lighter sialic blocks, which form the continents, float on a layer of viscous fluid mantle.
● Proposed that the major landmasses of the Earth were once united as a single super-continent called Pangaea.
● Pangaea broke into smaller continental plates, which moved apart as they floated on the mantle.
● Break up of Pangaea began as a rift valley.
● Mid-oceanic ridges mark where continents were once joined.
● Trenches formed where plates come together (site of major earthquakes & active volcanism).
● Suggested speeds from 0.3–36m/year, and the fastest at the moment is Greenland, which separated from Europe 100 000 years ago.
● The forces that cause the movement are radioactive. Whatever they were, they are not catastrophic.
● Ongoing forces are are moving these plates & there’s a continuous movement.
Plate tectonics attributes regarding evidences & discoveries? (4)
• Hard evidence came about 50 years after Wegener’s proposal.
• Best-fit data, Carey (1955) & Bullard (1965).
• Coastal is not the edge of the continental shelf.
• Discoveries about ocean floor/evidences for plate tectonics.
Discoveries about the ocean floor/Evidences for plate tectonics? (4)
● Ocean floor basalt under a layer of sediment.
● Mid-oceanic ridges & trenches.
● Age of sea floor was never older than 200 million years (young over the entire ocean of Earth).
● Magnetized Fe & Titanium oxides.
Magnetism of the sea floor attributes? (3)
• Happened many times through history.
• Patterns were found to be mirror images.
• Position of N is not constant & every so often reverses (the polarity of the N & S poles switches).
Magnetism of the sea floor process? (4)
● When magma is still fluid, crystals containing magnetized Fe & titanium oxides can align with the Earth’s magnetic field.
● Magma solidifies & the alignment is then frozen in position (indicates where N was at that time).
● Patterns were found to be mirror images.
● Position of N often reverses (not constant) & polarity of the N & S pole switches.
Iceland attributes in terms of ate tectonics? (3)
• Mid-oceanic ridge.
• One of the only places on Earth where the Mid-Atlantic Ridge is visible above sea level.
• Its formation was due to the movement of tectonic plates along the Mid-Atlantic Ridge.
Sial attributes? (5)
• Collectively called sima.
• Largely composed of basaltic rock.
• Less dense.
• Thicker.
• Less magnetized..(than those on ocean floor).
Elements to consider when talking g about plate tectonics? (3)
• Silica (Si).
• Al (Aluminium).
• Mg (Magnesium).
Site of major earthquakes & active volcanism?
Places where trenches were formed where plates come/came together.
Image of the world’s tectonic plates attributes? (6)
• 7 main plates.
• ~15 small plates.
• Arrows show direction of plate movement.
• If arrows are moving in different directions, we know there are fractures between these areas.
• An entire plate is often under different stressors & could be turn apart.
• Where arrows move together (point towards each other) = area of subduction.
Area of subduction diagramatically?
= area where arrows move together/point towards each other.
Subduction?
= area where an oceanic plate runs into a continental plate & slides beneath it.
African tectonic plate attributes? (2)
• There are no subduction zones around Africa.
• There is a break between plates in the Red sea & Gulf of Aiden.
Subduction of plates attributes? (6)
• Crust is consumed in subduction zones.
• Heat flow beneath the trenches is half that found on the abyssal plain.
• Gravity in the trenches is lower than in any other place on Earth.
• Trenches are also associated with more violent earthquakes & volcanism.
• When an earthquake epicentre is close to a trench, it is also shallow; deeper ones are further away (angle is ~45⁰).
• These are now termed Benioff zones.
Benioff zone?
= the area of the subduction zone where the hypocentre of an earthquake is found.
What drives plate tectonics?
We don’t know.
Why don’t we know what drives plate tectonics?
We don’t know because a lack of knowledge/theories on this component of plate tectonics theory is one of Wegener’s biggest weaknesses in promoting this concept as How can these plates move on a solid Earth?
The mechanism of plate tectonics attributes? (3)
● Continents are part of rigid plates of lithosphere & upper mantle (~100km thick).
● Temperature & pressure increase with depth but have opposite effects on rigidity.
● Results in the low velocity zone below the lithosphere (LVZ).
LVZ stands for?
Low Velocity Zone.
LVZ?
= zone where shock waves slow down due to increased pressure of the material (plastic consistency).
LVZ attributes? (2)
• AKA lubrication zone.
• 80-300km.
Explain the tectonic history of the Earth (bigger picture)?
Pangaea formed when southern (Gondwana) & northern (Laurasia) landmasses came together.
2 Things to note/consider when explaining/discussing the tectonic history of the Earth?
● The timeline/timeframe.
● What organisms were alive during these points in geological history (this is where your geological time scale comes into play).
Tectonic history of Earth “processes”? (5)
• Formation of Gondwana.
• Formation of Laurasia.
• Pangaea.
• Break up of Laurasia.
• Break up of Gondwana.
Formation of Gondwana attributes? (3)
● Made up of continental crust that now forms S. America, Aftica, Madagascar, Arabia, India, Seychelles, Australia, Tasmania, New Guinea, New Zealand, New Caledonia & Antarctica.
● Formed ~650mya during the Precambrian.
● Remained relatively stable & continuous even though it did drift as a unit between the equator & the poles.
Continents & Countries associated with Gondwana? (12)
• S. America.
• Africa.
• Madagascar.
• Arabia.
• India.
• Seychelles.
• Australia.
• Tasmania.
• New Guinea.
• New Zealand.
• New Caledonia.
• Antarctica.
Formation of Laurasia attributes? (4)
● Remained fragmented & isolated until the Devonian (~400mya).
● Some of the landmasses that made up Laurasia drifted from sub-Antarctic regions.
● Had a much more unstable & transitory history than Gondwana, even before the formation of Pangaea.
● Joined with Gondwana to make Pangaea during the Permian period (~240 mya).
Pangaea attributes? (6)
● Was only transitory & existent only for ~60 million years.
● During this time, you had a single landmass & a single sea (great connectivity).
● The breakup was initiated ~180 mya (early Jurassic).
● Land bridges between Gondwana & Laurasia were broken, transforming the Tethys sea into a circum-equatorial seaway.
● Tectonics before this is of marginal importance to biogeography (Y?).
● Important radiations occurred after the breakup of Pangaea (“Time of great vicariance”).
“Time of great vicariance”?
= when important radiations occurred after the breakup of Pangaea.
Breakup of Laurasia attributes? (2)
● Complex & there were periods when shallow seas invaded the continental areas.
● Mid-Cretaceous (100mya), a shallow sea separated western N. American, but a break opened between N. America & Europe (now the Atlantic ocean).
Breakup of Gondwana attributes? (7)
● Split between east coast of Africa & Madagascar, India and Australia (165mya).
● Then Africa & S. America separated from the rest of Gondwana.
● S. America split from Africa (110mya). Australia started rifting from Antarctica.
● New Zealand broke away, first from Australia & then from Antarctica (80mya).
● Madagascar split from India (60mya).
● Movement of India north very rapid, at 15cm/year, colliding with Asia 40-50mya, which pushed up the Himalayas.
● All continents but Antarctica drifted north.
What does the YouTube video on Pangaea show you?
