S3: W11 (Prof. Kelsey)

Question 1

Dispersal-Vicariance attributes? (5)

Answer 1

• 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.

Question 2

Hypotheses we consider in Dispersal-Vicariance? (2)

Answer 2

• Dispersal hypothesis.
• Vicariance hypothesis.

Question 3

Dispersal hypothesis?

Answer 3

= depends on the biology of organisms (do you know/are you provided with the biology of the organism?).

Question 4

Vicariance hypothesis?

Answer 4

= often the simplest explanation as it simply says that a mountain popped up & separated populations, resulting in their divergence (for example).

Question 5

Eg of Dispersal-Vicariance?

Answer 5

Panama isthmus.

Question 6

Explain Panama isthmus? (3)

Answer 6

● 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.

Question 7

Dispersal-Vicariance vs Secular migration?

Answer 7

● Secular migration
= species divergence due to adaptation.

● Dispersal-Vicariance
= species divergence due to separation/barrier.

Question 8

Thing to note about Panama isthmus eg?

Answer 8

Species pairs give you an idea of what causes divergence.

Question 9

Eg of Dispersal hypothesis/Dispersal?

Answer 9

Juncus.

Question 10

Eg of Vicariance hypothesis/Vicariance?

Answer 10

Northofagus.

Question 11

Explain eg of Juncus? (5)

Answer 11

● Wind-blown in roaring 40s.

● Little genetic structure.

● No common community links (no coupling of organisms).

● Volcanic islands & continents.

● Good eg of LJD.

Question 12

Explain eg of Nothofagus? (5)

Answer 12

● Seeds don’t survive in sea water.

● Strong genetic structure (high Fst).

● Community structure exists.

● Continental landmasses only.

● Phylogenetic relationships.

Question 13

Goelogical Time Scales (GTS) attributes? (6)

Answer 13

• 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.

Question 14

What is defining a time point based on? (2)

Answer 14

• Biodiversity during that time.

• Change in geology (chemical composition– Ur to Pb).

Question 15

Geology attributes? (2)

Answer 15

• ½ life of difference elements help you figure out the dates of time.

• Correlate to biodiversity by indicating a shift in biodiversity.

Question 16

Plate tectonics attributes? (6)

Answer 16

• 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.

Question 17

Why is Plate tectonics conclusive today? (2)

Answer 17

It’s because of:

• Evidence (direct & indirect).
• We know more about the mechanisms.

Question 18

Wegener’s continental drift attributes? (6)

Answer 18

• 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.

Question 19

What are the “things” that Wegener realized? (5)

Answer 19

● 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.

Question 20

Tillite?

Answer 20

= lithified till that is evidence of much older glaciation.

Question 21

What were Wegener’s insightful hypotheses? (10)

Answer 21

● 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.

Question 22

Plate tectonics attributes regarding evidences & discoveries? (4)

Answer 22

• 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.

Question 23

Discoveries about the ocean floor/Evidences for plate tectonics? (4)

Answer 23

● 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.

Question 24

Magnetism of the sea floor attributes? (3)

Answer 24

• 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).

Question 25

Magnetism of the sea floor process? (4)

Answer 25

● 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.

Question 26

Iceland attributes in terms of ate tectonics? (3)

Answer 26

• 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.

Question 27

Sial attributes? (5)

Answer 27

• Collectively called sima.
• Largely composed of basaltic rock.
• Less dense.
• Thicker.
• Less magnetized..(than those on ocean floor).

Question 28

Elements to consider when talking g about plate tectonics? (3)

Answer 28

• Silica (Si).
• Al (Aluminium).
• Mg (Magnesium).

Question 29

Site of major earthquakes & active volcanism?

Answer 29

Places where trenches were formed where plates come/came together.

Question 30

Image of the world’s tectonic plates attributes? (6)

Answer 30

• 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.

Question 31

Area of subduction diagramatically?

Answer 31

= area where arrows move together/point towards each other.

Question 32

Subduction?

Answer 32

= area where an oceanic plate runs into a continental plate & slides beneath it.

Question 33

African tectonic plate attributes? (2)

Answer 33

• There are no subduction zones around Africa.

• There is a break between plates in the Red sea & Gulf of Aiden.

Question 34

Subduction of plates attributes? (6)

Answer 34

• 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.

Question 35

Benioff zone?

Answer 35

= the area of the subduction zone where the hypocentre of an earthquake is found.

Question 36

What drives plate tectonics?

Answer 36

We don’t know.

Question 37

Why don’t we know what drives plate tectonics?

Answer 37

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?

Question 38

The mechanism of plate tectonics attributes? (3)

Answer 38

● 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).

Question 39

LVZ stands for?

Answer 39

Low Velocity Zone.

Question 40

LVZ?

Answer 40

= zone where shock waves slow down due to increased pressure of the material (plastic consistency).

Question 41

LVZ attributes? (2)

Answer 41

• AKA lubrication zone.
• 80-300km.

Question 42

Explain the tectonic history of the Earth (bigger picture)?

Answer 42

Pangaea formed when southern (Gondwana) & northern (Laurasia) landmasses came together.

Question 43

2 Things to note/consider when explaining/discussing the tectonic history of the Earth?

Answer 43

● The timeline/timeframe.

● What organisms were alive during these points in geological history (this is where your geological time scale comes into play).

Question 44

Tectonic history of Earth “processes”? (5)

Answer 44

• Formation of Gondwana.
• Formation of Laurasia.
• Pangaea.
• Break up of Laurasia.
• Break up of Gondwana.

Question 45

Formation of Gondwana attributes? (3)

Answer 45

● 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.

Question 46

Continents & Countries associated with Gondwana? (12)

Answer 46

• S. America.
• Africa.
• Madagascar.
• Arabia.
• India.
• Seychelles.
• Australia.
• Tasmania.
• New Guinea.
• New Zealand.
• New Caledonia.
• Antarctica.

Question 47

Formation of Laurasia attributes? (4)

Answer 47

● 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).

Question 48

Pangaea attributes? (6)

Answer 48

● 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”).

Question 49

“Time of great vicariance”?

Answer 49

= when important radiations occurred after the breakup of Pangaea.

Question 50

Breakup of Laurasia attributes? (2)

Answer 50

● 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).

Question 51

Breakup of Gondwana attributes? (7)

Answer 51

● 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.

Question 52

What does the YouTube video on Pangaea show you?