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ENVR 202 > L3 - Plate Tectonics > Flashcards

L3 - Plate Tectonics Flashcards

1
Q

To measure the evolution of the earth, we divide it into geological timescales (based on rock/fossil records). What are the 4 eons and their dates?

A

Hadean (4540-4000)
Archean (4000-2500)
Proterozoic (2500-541)
Phanaerozoic (541-0)

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2
Q

What are the 3 eras of the Phanerozoic?

A

Paleozoic (541-252)
Mesozoic (252-66)
Cenzoic (66-0)

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3
Q

What are three primary types of rocks?

A
  • Igneous “fire formed”: formed through the cooling and solidification of magma or lava (we can obtain absolute dates from igneous rocks)
  • Sedimentary: formed from chemical precipitates or fragments of earlier formed rocks (provide insight of relative dates of when which events occurred)
  • Metamorphic: formed by the application of heat and pressure to either igneous or sedimentary rocks
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4
Q

How do we date rocks?

A

Absolute dates: radiometric dating of igneous rocks
Relative dating: study the relationships between rocks (sedimentary)

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5
Q

What is radiometric dating?

A
  • We study the radioactive decay of an isotope and back-calculate to when that original rock started
  • We date the teeny-tiny microscopic minerals formed within the rocks
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6
Q

What is an isotope?

A
  • All atoms of a precise mass for a given element
  • Different number of neutrons gives for a different mass
  • Ex: C12 (stable), C13 (stable), C14 (unstable)
    • With radio-carbon dating, we can only go back 50 000 years
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7
Q

What are parent and daughter isotopes?

A

Parent Isotope: initial isotope, radioactive parent
Stable Daughter: the new element produced as a result of radioactive decay

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8
Q

What is the process of isotopic dating of rocks?

A
  • When the rock forms, you assume it contains a certain amount of this unstable parent isotope and NONE of the daughter isotope
  • Over time, as that rock ages, you will have less of the parent atoms and more of the daughter atoms
  • THUS, the rock can be accurately dated by determining the ratio of parent to daughter atoms
    **Isotopic signature
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9
Q

Why do we use isotopes as a dating indicator?

A
  • Their half-life (time required for half of the original population of radioactive atoms to decay) is exactly known
  • Therefore the relative concentrations of these isotopes within a rock or mineral can measure the age
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10
Q

What is the principle of superposition?

A
  • Sedimentary rocks allow us to infer an age or the date of an event based on the sequence
    • Bottom layers are the oldest, top layers are younger
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11
Q

How does relative dating work?

A
  • The appearance and disappearance of fossils are a good indicator of time
  • We can match rocks the fossils were found in to other rocks based on similar sequencing characteristics (even across very large distances)
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12
Q

Where do we find fossils?

A
  • Most abundant in marine sedimentary rocks
  • Generally not found in igneous or metamorphic rocks
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13
Q

What are challenges to dating with fossils?

A
  • Different levels of accumulation depending on where the fossil got deposited
  • Lack of sediment (e.g. a storm that removed sediment)
  • Too much sediment (e.g. a river may dump a large amount of sediment into the sea)
    **We can’t use the thickness of the rocks to estimate how much time has passed.
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14
Q

When was the Earth formed?

A
  • The Earth formed about 4.54 BYA out of a solar nebula (swirling cloud made up of bits and pieces left over from old stars that have exploded)
  • Gravity pulled in a bunch of dust and gas into this nebula and Earth became the third planet from the sun
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15
Q

What is the Goldilocks Zone?

A
  • Habitable zone: certain distance from a star where the temperature is just right (not too hot, not too cold for liquid water to exist)
  • This principle drives a lot of the search for life on exo-planets
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16
Q

What was Earth like during the Hadean Eon (4540-4000)?

A
  • Initially molten - what Hell would look like
  • Constant bombardment of asteroids and comets hitting the surface
  • Formation of the moon
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17
Q

Generally, how was the planet formed?

A
  • Constant heavy bombardments heated the Earth
  • This heating was also increased by gravitational contraction
  • Thus, we had the partial total melting of the Earth, creating a magma ocean
    • The iron-rich fraction of this liquid was heavier and it SUNK to Earth’s centre - creating the CORE
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18
Q

What was the composition of the earth 4.4 billion years ago (Ga)?

A
  • Iron Core + Mantle + Crust
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19
Q

What changes occurred on Earth by the end of the Hadean?

A
  • the Earth was cooled down enough to form rocks and oceans
  • Steam in the atmosphere cooled down and fell as rain to create oceans
  • First continents begin to form
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20
Q

How do we know this?

A
  • Oldest piece of Earth’s crust/solid land comes from Western Australia
    • Conducted isotopic dating on Zircon crystals: 4.4 Billion years
    • Thus, within the first 100-100M years of our planet, there was enough cooling to form crust
  • ALSO: ratio of oxygen isotopes within this zircon crystal indicate that the crystal likely formed in a cool, wet process at the Earth surface
    • Suggests: parts of the Earth may have been covered with liquid water (at 4.4 Ga years ago)
21
Q

What was Earth like during the Archean eon (4000-2500)?

A
  • Liquid water was prevalent (lots of evidence for this)
  • First evidence of life is dated back to the Archean
  • Onset of plate tectonics
22
Q

What is plate tectonics?

A
  • All of the crusts on the planet move around like floating slabs of rock (~96km thick) on top of hot, mushy rock in the mantle
  • Earth is constantly RECYCLING itself: creating new land and sub-ducting itself back into the mantle
23
Q

What is continental drift?

A
  • First proposed by Alfred Wegener in 1915
  • Suggested that the continents of the Earth moved around over geologic time relative to each other, thus appearing to have “drifted” across the ocean bed
  • Explanation to why animals and plant fossils, and rock formations are found on different continents (that were separated by oceans)
24
Q

If continental drift had not occurred, what are the alternative explanations?

A
  • Species evolved independently on separate continents – contradiciting Darwin’s theory of evolution
  • Species swam to other continents (Noah’s Arc)
25
Q

What is the evidence against these alternative hypotheses?

A
  • Mesosaurus, a freshwater reptile that lived between 286-258 MYA, are found solely in Southern Africa and Eastern South America
    • It would have been physiologically impossible, based on the fossils, for it to have swum this distance
  • Rocks across the ocean were the exact same age and fit together really nicely like puzzle pieces
26
Q

When did the theory of continental drift emerge into tectonic plates?

A
  • 1950s: Wegener suggested that the rotation of the Earth caused the continents to shift towards and a part from each other
  • 1970s: Today we know that continents because they rest on tectonic plates that are always moving and interacting
27
Q

What is the structure of the Earth?

A
  1. Core
    - Rich in Iron
    - Inner-core is solid and the outer-core is liquid (source of the Earth’s magnetic field)
  2. Mantle (very very hot rocks)
    - Rich in silicon and oxygen
  3. Crust (cooler, stiffer rocks)
    - Also, rich in silicon and oxygen
28
Q

What are tectonic plates made of?

A
  • Rigid, cool lithosphere
  • Lithosphere: rocky crust of the ocean floor and continents down to the upper mantle
  • They sit on top of the hot and mushy mantle
29
Q

What are the two types of crust on Earth?

A
  • Oceanic: much thinner (7km thick), its chemical composition makes it very dense (sinks under continental crust), younger
  • Continental: much thicker (10-70km), buoyant, mostly old rocks
30
Q

Plate tectonic characteristics on Earth

A
  • Earth’s crust is divided in 12 major plates
  • Earth’s structures like volcanoes, mountains, ocean trenches, are caused by plate interactions (collision, pulling apart, scraping)
  • Tectonic: deformation of the crust as a consequence of plate interaction
31
Q

What causes the plates to move?

A
  • Tectonic plates sit on a mantle, and the mantle has convection currents that drive plate tectonics
  • Conveyor belt = convection cells in mantle
32
Q

Plate boundaries = Zones of contact between plates

A
  • Divergent: moving away
  • Convergent: moving towards one another
  • Transform: moving against one another
33
Q

What are divergent boundaries?

A
  • The space created by plates moving away from each other can be filled with new crustal material sourced from molten magma from below
34
Q

How do divergent boundaries produce rifts in continental crusts?

A
  • If the rift opens wide enough, it will form the thin rocky floor of a NEW OCEAN
    • E.g., East African Rift, Iceland being slowly torn apart by continental rifting
35
Q

How do divergent boundaries produce mid-ocean ridges?

A
  • Mid-ocean ridges: divergent boundaries between oceanic plates (MOST ACTIVE)
    • As they move apart, small amounts of magma rise to the sea floor and add new crust - sea floor spreading
  • Mid-ocean ridges systems form some of the most extensive mountain ranges on Earth, they’re just under water
    • Mid-Atlantic ridge: separated the North American Tectonic Plates from the Eurasian ones (40 000 km in length)
36
Q

What are Black smokers/hydrothermal vents?

A
  • Sea floor hot springs: molten hot magma heats up the water and pushes it up through the vent - found along mid-ocean ridges
  • Entirely different ecosystem of organisms that we never new about
  • Organisms at these vents get their energy from the vent itself and not sunlight (because it is so deep-down)
    • Potentially place where life started??
37
Q

What are convergent boundaries?

A
  • Plates colliding: a denser plate is sub-ducted underneath the less dense plate. The plate being forced underneath will eventually get melted and destroyed (and recycled)
38
Q

How does continent-continent collision work?

A

Both continental crusts are too light/buoyant to be subducted so a continent collision occurs creating especially large mountain ranges
- E.g. Himalayas

39
Q

How does continent-oceanic collision work?

A

Denser oceanic plate is subducted, often forming a mountain range on the continent
- E.g., the Andes

40
Q

What are subduction zones?

A
  • Occur when one or both of the tectonic plates are composed of oceanic crusts
  • Leads to oceanic crust being recycled
41
Q

How does ocean-ocean collision work?

A
  • One oceanic plated is eventually subducted under the other
    • Formation of deep trenches
    • E.g., Mariana Trench - 11km deep, deepest place on Earth
42
Q

What are transform boundaries?

A
  • When plates rub against each other, huge stresses are set up that can cause portions of the rock to break = resulting in earthquakes
    • Faults: places where plates break
    • No destruction or new formation of crusts
43
Q

Which boundaries are most prevalent on Earth?

A
  • Convergent & Divergent
  • Very small amount of transform boundaries
44
Q

How fast do plates move?

A
  • Really slow: a few cm per year (rate at which your fingernails grow)
45
Q

How do plate tectonics affect the evolution of life?

A
  • Plate tectonic movements affect geography and could in turn affect food supply, climate, and diversity of life – could create or destroy niches
  • Formation of Grand Canyon: squirrels and other small mammals were separated and could not reproduce with each other across this new GEOGRAPHIC BARRIER
46
Q

What is the Pangea?

A
  • A supercontinent composed of earlier continents (Europe, North America, Souther America, Africa all attached)~335 MYA
  • Began to break a part ~ 175 MYA
  • Terrestrial organisms could migrate across all continents and were only limited by their biotic potential
47
Q

Breaking of the Pangea = Promotion of Biodiversity

A
  • Creation of physical barriers such as seas
  • Species were separated and exposed to different physical (climate) and biotic (change in predators) conditions
  • Each species would then begin to adapt very differently and new species emerge
  • New habitats were also created due to a change in biotic and abiotic factors such as climate
48
Q

What is weathering? How are plate tectonics related?

A
  • The (slow process of) breakdown of minerals in rocks at or near the Earth’s surface – releasing nutrients
  • Weathering is caused by chemical and physical interactions with air, water and living organisms
  • All the nutrients found in oceans come from weathering and erosion of rocks
  • When weathering and erosion rates are higher, we should also see an increase in nutrients supplied to the oceans
    • Relationship between an increase in nutrients in the oceans due to plate tectonics and bursts of evolutionary change ??? TBD
49
Q

How do plate tectonics influence habitability?

A
  • Are plate tectonics necessary for life on Earth?
  • They can help to regulate the planet’s temperature, recycles nutrients, created hydrothermal vents, created new niches?
  • Earth is the only accepted planet known to have plate tectonics

ENVR 202 (22 decks)

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