Week 2- Origin, life cycle and sediments of the ocean Flashcards
When was the beginning of the universe?
14 billion yrs ago
When was earth formed?
4.5-4.6 bya
What is Accretion?
Bits come together to form the earth
How do we know that the earth is that old?
Rocks
Uranium led dating
Earth’s first atmosphere
Mainly H and He stripped solar wind
Earth’s second atmosphere
- Mainly CO2 and water vapour (H,N and sulphur-based gases)
- Formed by outgassing (burping gases to the surface)
- earth starts to become solid but is not yet liveable
Ocean formation
- 3.8-4.2 Ga
- water vapour cools and forms droplets, rain falls to earth and fills depressions
Early life on earth
Cyanobacteria (blue green algae)
3.5 Ga
Great oxidation event
Cyanobacteria photosynthesize and produce O2, creating the third atmosphere
2.4 Ga
Where did life most likely originate?
At hydrothermal vents in the early ocean
Why did life mostly originate in hydrothermal vents?
Protected from meteorites that hit the ocean surface
Warm, alkaline environment (ideal conditions)
Created self-assembling protocells
What type of organism lived at hydrothermal vents?
Extremophiles (achaea)
- live in extreme conditions and metabolize sulphur
Stromatolites importance
Led to the accumulation of breathable oxygen and evolution of multicellular life
What is the Wilson cycle?
Explains how oceans are created and destroyed
400 million year cycle
Which stages of the wilson cycle are opening the basin?
Stage A, B and C
What stages of the wilson cycle are closing the basin?
Stage D, E, F
Wilson cycle Stage A: Embryonic
Rifting: earth’s crust is stretching and cracking; fissures form, faulting occurs
- rift valley forms
- subsidence (early stage of ocean formation)
Example of Stage A
East Africa rift
Wilson cycle Stage B: Juvenile
Oceanic rift zone: going to be an ocean forming
- widening of rift valley
- crust is thinning
- subsidence and connection to ocean (ocean water comes in to fill rift valley
Example of stage B
Red sea
Wilson cycle stage C: Mature
- Continued lateral spreading of rift valley
- Widening generation of new ocean crust
- Increasing sedimentation
- Geologically passive margins
Example of stage C
Atlantic
*every year is gets wider
Wilson cycle stage D: Declining
- Convergence (ocean starts getting smaller)
- Increasing subduction
Example of stage D
Pacific
*pacific plate is sub ducting underneath the Asian plate
Wilson cycle stage E- Terminal
- Continents moving together
- Subduction of ocean crust
- Narrowing of sea
- volcanic eruptions, earthquakes, uplift and mountain building
Example of stage E
Mediterranean sea
Wilson cycle stage F- Suturing
- Continent collision; ocean completely gone
- Uplift of continental crust
- Subduction of oceanic crust
Example of stage F
Himalayas
*Indian plate has slammed into the Eurasian plate
Proof of Wilson cycle
Limestones (form in marine environment) found on top of Mt. Everest
What are sediments?
Particles (grains) of organic or inorganic matter that accumulate in a loos, unconsolidated form
What scale is the grain size of sediments measured on?
Wentworth scale
Types of sediments grain size
Fine grained (small)
Coarse grained (large)
Sedimentary rock
Occurs when sediments are lithified/cemented together
Size of common marine sediments (SMALL-LARGE)
- Clay
- Silt and sand
- Pebbles
- Cobbles
- Boulders
*last three are considered gravel
What can grain size tell us?
Info about transport, depositional conditions and energy of the environment
Ex. finer grain sediments don’t require as much energy to move
Settling
Process by which grains settle to the bottom of the ocean and from a sediment layer
*can depend on grain size
Time is takes for sediments to reach the ocean floor
Sand= 2 days
Silt= 6 months
Clay= 50 yrs
4 sediment types
- Terrigenous (lithogenous): from land
- Biogenous: remains of marine organisms
- Hydrogenous: precipitate directly from seawater
- Cosmogenous: from space
Shallow water marine sediments
Neritic
- terrigenous
Deep water marine sediments
Pelagic
- Biogenous
Hydrogenous sediments
Less than 1% of the sediments in the ocean
Includes metal sulphides and manganese nodules
Manganese nodules
Polymetallic (Mn, Fe, Ni, Co, Cu)
Slow precipitation
They would not from where other sediments accumulate bc if they were covered they could not grow
Cosmogenous sediments
Alien (extraterrestrial) sediments
- tektites (interplanetary dust)
Terrigenous sediments
99% of sediments are terrigenous
Greatest amount in ocean close to land
Processes involved in sedimentation
- Erosion/weathering
- Transportation
- Deposition
What is a common component of terrigenous sediments?
Quartz(SiO2)
Why is quartz important?
- One of the most stable minerals on the planet
- Can be transported ling distances
Sources of terrigenous sediments
- Volcanic eruptions
- Wind blow sediment from desert
- Sediment carried far out over ocean
- River transport and discharge of eroded material
Biogenous sediment
Produced by marine organisms as shells or other hard body pats that are either calcareous (CaCO3) or siliceous (SiO2)
Where do biogenous sediments come from?
Tests or shells of microscopic organisms
Microscopic organisms that contribute to biogenic sediments
Foraminifera
Coccolithophores
Radiolarians
Diatoms
How do foraminifera and coccolithophores create shells?
Calcareous (CaCO3)
How do radiolarians and diatoms create shells?
Siliceous (SiO2)
Coccolithophores
Covered with small plates made of CaCo3
Create think deposits of ooze
What is an ooze?
Very fine pelagic sediment that can either be calcareous or siliceous
*Must be at least 30% biogenous for it to be an ooze
Foraminifera
CaCO3 secreting single-cell organisms
Radiolarians and Diatoms
SiO2 secreting
Diatoms =single celled algae
Radiolarians= single-celled
Calcite compensation depth (CCD)
The depth at which the amount of calcium carbonate delivered to the seafloor is equal to the amount removed by dissolution
*Marine snow is not visible below it
CCD and dissolution
If CaCO3 sinks below the CCD it will dissolve
If CaCO3 remains above CCD it will accumulate
Calcite compensation depth conditions
More acidic (low pH)
Lower temp
High CO2
High pressure
Lysocline
Depth at which a rapid increase in dissolution occurs
Lysocline depth in the Atlantic
5500m
Lysocline depth in the Pacific
4500m
*shells in the pacific dissolve at a shallower depth
Why is there variable depth of the lysocline in the Atlantic vs the Pacific?
Deeper in Atlantic bc it’s warmer and pH is less acidic
What conditions lead to increased solubility?
Increased CO2 content (the more CO2 the more CaCO3 dissolves)
Decreased temp (leads to more CO2 held in water)
Increased pressure
CCD and calcareous ooze distribution
- Calcareous ooze deposited on the mid-ocean ridge
- Calcareous ooze is covered and protected (abyssal clay and SiO2 ooze)
- Sea floor spreading moves calcareous ooze beneath the CCD into the deep water
Distribution of marine sediments
Calcareous sediments- mid latitudes (warmer, tropical waters)
Siliceous - high latitudes (colder water)
*****What can collecting sediment cores tell us?
Climate change
Geology
Earth history
Evolution of life
Verify scientific theories
How do we know what the ocean floor looks like?
Rely on the five S’s
- Soundings
- Sonar (soundwaves)
- Submersible
- Seismic
- Satellite
Types of remote sensing
Detects energy reflected from Earth
Detects subtle changes in ocean surface
What do ocean basins look like?
- Continental margin
- Deep ocean basin
- Mid ocean ridge
Continental margin
Submerged outer edge of a continent
Deep ocean basin
Deep sea floor beyond the continental margin
Active continental margin
Narrow continental shelf, steep slope, thinner sediment cover
- seismic and volcanic activity, orogeny
- coincides w plate margins
-active techtonism occurs
Passive continental margin
Wide continental shelf, gentle slope, think sediment cover
- range from volcanic activity to no volcanic activity
- does not coincide with plate margins
-far from techtonic plate
Continental shelf
Relatively flat edge of a continent where a country extends to
- exposure during low sea-levels
- underlain by granitic crust
- biologically-rich, economically significant
Continental slope
True edge of a continent
- starts at a shelf break
- presence of submarine canyons
Submarine canyon
Narrow, steep-sided underwater valley that erodes into the continental shelf and slope
*primary transport pathways for terrigenous sediment reaching abyssal seafloor
Deep sea fan
When a submarine canyon ends in a fan shaped sediment wedge
Underwater avalanche that erodes and canyons and forms turbidites
Where are submarine canyons more common?
Along active continental margin
Turbidity currents
Quickly moving down flow slope of dense sediment-laden water
Fluidized flow
Flow of sediments start fast, depositing large sediments which pile up and eventually slows the flow down resulting in a turbidite
Continental rise
Where we reach the true deep ocean
Sediment accumulation, turbidites, deep sea fans underlain by oceanic crust
Abyssal plains
Flat, most featureless areas of the earth
Suspension settling
Accumulation of fine-grained sediment
Occurs at abyssal plains
How is sediment thickness controlled in an abyssal plain?
Age
Distance from continent and trench
Abyssal hill
Elevated areas in deep ocean basins
Most abundant geomorphic feature on earth
<1000m high
Seamounts
- circular/elliptical feature
>1000m in height - steep slopes
- underwater volcano
Guyots
- flat topped
- eroded by waves
Trenches
Long, narrow depressions on the seafloor
One plate sub ducting under another plate
Formed by techtonic processes
Island arc
Curving chain of volcanic islands occurring around the margin of ocean basins
Always forms on concave side of trench
Where is the trench wall always steeper?
On island arc side
Marie Tharp and mid ocean ridges
First to map topography of ocean floor and prove mid-ocean ridges exist
Mid ocean ridge
An elevated region with a central valley on an ocean floor at the boundary between two diverging tectonic plates where new crust forms from upwelling magma
*basaltic rock
Fast spreading ridge
Magma is hotter and flows easier
ex. East pacific rise
Slow spreading ridge
Colder, plate more brittle (breaks and forms normal faults)
ex. northern mid- atlantic
Transform faults
- Two tectonic plates slide past one another
- May occur in the portion of a fracture zone that exists between different offset spreading centres
- Offsets mid-ocean ridge pattern
Fracture zone
Linear feature on the ocean floor resulting from the action of offset mid-ocean ridge axis segments
- Due to plate tectonics
Who first discovered hydrothermal vents?
Robert Bellard in 1977
White smokers (hydrothermal vents)
Super hot water comes in contact with ocean water
30-350 degrees celcius
Black smokers (hydrothermal vents)
Greater than 350 degrees celcius
Metal sulphides present
What lives at a hydrothermal vent and what process do they perform?
Extremophiles
- Chemosynthesis
Can hydrothermal vents go extinct?
Yes
Can lose magma source
