unit 3 geology - schoolwires...seafloor spreading oceanic plates are diverging from one another...
TRANSCRIPT
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MRS. STAHL
MARINE BIOLOGY
Unit 5 & 6 Geology of the Ocean,
Water, Waves, and Tides
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Some Facts
Solar system was formed more than 5 billion years ago, with Earth forming 400 million years later.
Surface was so hot that water could not remain there because there was no free oxygen gas in the atmosphere
Ocean began forming 4.2 billion years ago
Life first evolved in the ocean
Ocean covers 70.8%
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How did the ocean form?
Hypothesis: Earth was composed of cold matter and over time energy from space and radioactive decay caused the temperatures to rise.
Process continued for several hundred million years until the core of the Earth was hot enough to melt iron and nickel.
Elements melted -> moved to the core-> raising temps to 2,000 C
Molten material moved to the surface, spread out, continued to melt and solidify, creating our landscape, separating the lighter elements from the denser ones.
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They think that if there was any water present, it was stored up in the Earth’s minerals. Then, with continuous heating and cooling the water vapor was carried to the surface, it cooled, condensed, and formed the ocean!
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Video
http://www.history.com/shows/how-the-earth-was-made/videos/oceans
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Origin of Life Atmosphere was originally made up of gases like
carbon monoxide, carbon dioxide, methane, nitrogen, and ammonia. Oxygen is chemically active, so any other free oxygen gas present would have combined with some other element forming oxides. Therefore, oxygen did not start to accumulate in the atmosphere until the evolution of modern photosynthesis.
Oxides- Chemical compound containing at least one oxygen atom as well as another element.
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Biologists also theorize that the molecules (carbon monoxide, carbon dioxide, nitrogen, methane, and ammonia) formed and accumulated in the ocean and over time the ocean turned into a huge, highly concentrated bowl of nutrient soup.
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The molecules then became organized and the first cells evolved.
There wasn’t any oxygen so the first cells had to be anaerobic.
The first cells were also heterotrophs, or relied on others for food.
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The oldest marine fossil is marine bacteria (cyanobacteria), which was found in NW Australia, and is estimated to be between 3.4 and 3.5 billion years old.
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The Ocean Today
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The Ocean Today
139 million square miles, 362 X 10^18 gallons
362,000,000,000,000,000,000 gallons of water
Largest habitat on the planet
Referred to as the world ocean
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There are four major basins, but five oceans
1.Pacific
2.Atlantic
3.Indian
4.Arctic
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The area around Antarctica is referred to as the
Southern or Antarctic
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Body of Water Define Examples
Sea Body of
saltwater that is smaller than an
ocean and landlocked.
Mediterranean Sea
Red Sea Caribbean Sea
Gulf Smaller body of
water that is mostly cut off
from the larger ocean or sea by land formations.
Gulf of California
Gulf of Mexico
Persian Gulf
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Label the oceans and continents
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Continental Drift
The movement of the seafloor caused by the continuous movement of the continents that rest on it.
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The seafloor is constantly being replaced with new seafloor, therefore, organisms have to adapt constantly.
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Lithosphere Asthenosphere
- Rock Sphere
- Tectonic plate
- Very strong
- Weak
- Easily deformed layer of
the Earth
- Acts as a “lubricant” for
the plates to slide
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Oceanic Crust Continental Crust
- Basalt
- Thin crust under the
oceans
- Thinner and denser
- More active
- Granite
- Floats on top of mantle
- Makes up the
continents
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19th Century
Edward Suess
Early 1600’s
Sir Frances Bacon
1915
Alfred Wegener
1960’s H.H. Hess
Continents may have once been connected to each other.
Proposed Gondwanaland- fusion of Southern Continents (S. America, Africa, India, Antarctica, and Australia).
One supercontinent= Pangaea. Forces of the Earth’s rotation separated the continents.
Molten rock / Magma in the mantle moved by convection currents (heating and cooling of magma).
Moving Continents
Timeline of Moving Continents
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Pangaea
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The man of Pangaea is
Alfred Wegener
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Evidence of Continental Drift
1. Continental plates fit together like a puzzle.
2. Distribution of Earthquakes -> occur in narrow zones that correspond to areas along ridges and trenches. Most active areas of crustal movement.
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3. Temperature of sea bottom-> highest temps at ridges. Temps decrease with distance from ridges. Why do you think that is?????
Heating magma oozing out.
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4. Age of rock samples from seafloor. Youngest rock was found near ridges and older rocks were found further away.
5. Fossils collected on opposite coasts were similar.
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6. Coal deposits and other geological formations matched up on opposite sides of the Atlantic.
7. Sediment gets thicker and thicker as you move away from the ridges.
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8. Seafloor Spreading-> basalt magma from the mantle rises to create new ocean floor at mid-ocean ridges. On each side of the ridge, seafloor moves from the ridge towards the deep sea trenches, where it is subducted or sucked back in and recycled back into the mantle.
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9. Magnetic evidence->
* 170 reversals in the past 76 million years (north / south polarity switched back and forth). Reverses directions.
* Caused by fluctuations in the movement of material in iron-nickel outer core.
* When rocks are in the molten stage they are free to move around and act like tiny little compasses pointing either north or south.
* When the rocks cool they keep whatever their orientation is. There are literally stripes on the rocks that show the magnetic bands and they match up on either side of the mid ocean ridge= magnetic anomalies.
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Continental Drift was not accepted at first because:
Scientists thought that he did not have enough evidence to prove his theory.
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Laurasia consisted of: Europe, Asia, and North America
Gondwanaland- S. America, Africa, India, Antarctica, and Australia
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The Forces that Drive Continental Movement
HH Hess Convection currents- the way magma moves. Magma
rises from the Earth’s core to the upper mantle, because it’s less dense than the surrounding material. When it reaches the mantle it cools, becomes denser, and sinks back into the core. The recycling causes changes in temperature called convection.
Volcanoes form when the magma breaks through the Earth’s crust.
Lines of volcanoes form underwater mountain ranges = midocean ridges
When it cools, it forms new crust = oceanic basaltic crust https://www.youtube.com/watch?v=MmMX83diwl0
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Rift Valley
Where the Earth’s crust is splitting apart Narrow, steep sides, flat floor Looks like a ditch Created by tectonic activity High volcanic activity.
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Tanzania’s Great Rift
Valley
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Fracture Zones-
Linear regions of unusually irregular sea bottom.
Almost like cracks in the crust
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SUBDUCTION ZONES
Regions where the old material sinks down into the mantle, and when it hits the magma of the mantle, it liquifies and recycles itself through convection currents back into the core.
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Seafloor Spreading
Oceanic plates are diverging from one another
Magma rises along a rift zone and spreads out at the surface building new seafloor.
The age of the rocks increases as one moves away from the rift zone.
The mid-oceanic ridge is the primary site for seafloor spreading.
Earthquakes and volcanoes are where seafloor spreading is occurring.
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Theory of Plate Tectonics
The lithosphere is viewed as a series of rigid plates that are separated by earthquake belts that are located around trenches, ridges, and faults.
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Seven Major Plates are:
1.Pacific
2. North American
3. Eurasian
4. South American
5. African
6. Antarctic
7. Australian
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Where plate boundaries move apart and new lithosphere is formed
divergent plate boundaries occur. Where the old lithosphere is
destroyed because the plates move toward each is called convergent
plate boundaries.
Where the plates move past each other = Faults.
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Transform Fault
Each side is formed by a different plate and the plates scrape against each other
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Divergent Boundary- plates move away from each other
Produce earthquakes and volcanoes
When they pull apart= earthquakes
Magma increases = volcano
Magnetic anomalies= proves that the ocean plates are moving.
Mid-ocean ridges are created
Mid-Atlantic Ridge (moves N. America and Europe further apart)
Convection Currents
Seafloor Spreading
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Convergent Boundary- plates move together
Produce mountain chains= earthquakes
Subduction zone-> oceanic crust subducts back into the mantle
Ring of Fire
Continental crust is buoyant and less dense so one plate doesn’t easily override another.
Himalayas-> Indo-Australian Plate pushes into the Eurasian Plate (India vs. China)
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Transform Fault- plates slide past each other
Earthquakes
San Andreas Fault in CA (where the N. American and Pacific plates)
Mid-ocean ridge
https://www.youtube.com/watch?v=JmC-vjQGSNM
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Rift Zones
Where the lithosphere splits, separates, and moves apart as new crust is formed.
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Rift Communities / Deep Sea Vents
Thriving communities of marine organisms
Depend on chemosynthetic activity of bacteria for their nutrients.
Represent food webs that exist in the absence of sunlight.
https://ocean.si.edu/ocean-videos/hydrothermal-vent-creatures
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The Ocean Bottom
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Bathygraphic Features
Physical features of the ocean bottom
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The ocean bottom is divided into two different regions the continental margin and the ocean basin.
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Continental Margins
Region that lies beneath the neritic zone.
Consists of continental shelf and continental slope
Composed of granite that is covered by sediment and have similar features to the edge of the nearby continent.
See Figure 3-12 on page 56 to discuss the formation of the continental shelf.
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Continental Shelf
Generally flat areas
40 miles wide and 430 feet deep
Slopes gently toward the bottom of the ocean basin
Produced by waves that constantly erode land mass and by natural dams, reefs, rocks, and volcanic barriers.
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Continental Slope Transitional level
Shelf break is where the shelf ends and the slope begins
Shelf break is where there is a rapid change in depth to the seafloor
Less sediment
Submarine Canyons-> aligned with river systems on land and they create a ripple effect on the sea floor. At the end it fans out = Deep Sea Fan.
They are formed by turbidity currents = underwater avalanches of sediment (large accumulations of sediment collapse).
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Continental Rise
Small slope at the base of the continental slope. Created by landslides that carry sediment to the bottom of the slope.
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The Ocean Basin:
Seafloor
Four Main basins: Pacific, Atlantic, Indian, and Arctic
Composed of basalt rock covered with a thick blanket of sediment.
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Abyssal Plains and Hills
Bottom of the ocean basin
Flat
Formed by sediment from turbidity currents
Spread out on the ocean floor are abyssal hills (3300 ft. high).
Formed by volcanic activity
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Seamounts
Steep sided formation that rises sharply from the bottom.
Formed by underwater volcanoes
Some show us coral reef activity and erosion proving that they may have been above water at one point in time.
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Ridges and Rises
Series of large, underwater volcanic mountains that run through every ocean.
Separates the ocean basins
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Trenches
Most common in the Pacific Ocean
Marianas Trench-> the deepest spot on the Earth is the Challenger Deep and is 6.85 miles deep.
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The Ocean Floor
Continental shelf is very productive because it relatively shallow and provides lots of sunlight and nutrients.
Abundant marine life on the shelf
No sunlight in the abyss.
Limited to chemosynthetic bacteria in vent communities
Ocean floor organisms rely heavily on organisms falling from above.
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Composition of the Seafloor
The entire seafloor is made up of basalt rock with a blanket of sediment on top.
Sediment is made up of:
Living organisms
Land
Atmosphere
Sea that accumulates over time
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Why is the sediment so important to organisms that live on the continental
slope, shelf, or abyssal plains?
Provides a habitat for many organisms and a source of nutrients for others.
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Five types of sediment:
Biogenous
Hydrogenous
Terrigenous
Cosmogenous
Lithogenous
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Hydrogenous Forms when dissolved materials come out of a
solution such as a precipitate.
Precipitation is caused by changes in temperature, pressure, and chemically active fluids.
Types include manganese nodules (ore material in the ocean that comes from terrigenous and volcanic, and also hydrothermal material), phosphates, evaporative salts, metal sulfides, and carbonates (rocks with high amounts of calcium).
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Lithogenous Composed of fragments of pre-existing rock
material
Formed by physical and chemical weathering-> break-up of exposed rock, movement of sediment, and large particles of rock that are deposited near the edges of the continents and it accumulates
Most is made up of quartz
Where is it found? -> neritic zone (near shore), beaches, continental shelves, pelagic zones (deep sea floor).
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Biogenous
Skeletons and shells of dead marine organisms.
Biogenous ooze= made up of 30% of microscopic shells. When it hardens it turns into rock and can make chalk or diatomaceous earth.
Calcareous ooze= calcium carbonate= coccolithophorians and foraminiferans
Silicareous ooze= silica= radiolarians and diatoms
Found in the pelagic zone
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Foraminiferans
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Coccolithophorians
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Radiolarians
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Diatoms
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Terrigenous
Found in the deep sea and is formed by accumulation of turbidites
Turbidites are sea-bottom deposits formed by massive slope failures where rivers have deposited large deltas. These slopes fail in response to earthquake shaking or excessive sedimentation.
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Turbidites
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Cosmogenous
Composed of material from outer space
Space dust and meteor debris
Forms an insignificant amount of ocean sediment