Exam 1
What is the age of Earth?
4.6 billion years old
Describe the sea floor spreading and why it was an important piece of evidence in support of plate tectonics.
A process producing the lithosphere when convective upwelling of magma along the oceanic ridges moves the ocean floor away from the ridge axes at rates between 2 to 12 centimeters (0.8 to 5 inches) per year. the concepts of continental drift and sea floor spreading have been united into a much more encompassing theory known as plate tectonics, which describes the movement of the outermost portion of Earth and the resulting creation of continental and sea floor features.
Describe the differences between transform faults and fracture zones
A transform fault is a seismically active area that offsets the axis of a mid-ocean ridge. A fracture zone, on the other hand, is a seismically inactive area that shows evidence of past transform fault activity. Across a transform fault, two lithospheric plates are moving in opposite directions. Across a fracture zone (which occurs entirely within a plate), there is no relative motion because the parts of the lithospheric plate cut by a fracture zone are moving in the same direction (Figure 3.24). Transform faults are actual plate boundaries, whereas fracture zones are not
Describe the origin, composition, texture, and distribution of biogenous sediment.
iogenous sediment begins as the hard parts (shells, bones, and teeth) of living organisms ranging from minute algae and protozoans to fish and whales. The two most common chemical compounds in biogenous sediment are calcium carbonate (CaCO3, which forms the mineral calcite) and silica (SiO2). The distribution of biogenous sediment on the ocean floor depends on three fundamental processes: (1) productivity, (2) destruction, and (3) dilution.
Describe the origin, composition, texture, and distribution of lithogenous sediment.
is derived from preexisting rock material that originates on the continents or islands from erosion, volcanic eruptions, or blown dust All rocks are composed of discrete crystals of naturally occurring compounds called minerals. One of the most abundant, chemically stable, and durable minerals in Earth's crust is quartz. All rocks are composed of discrete crystals of naturally occurring compounds called minerals. One of the most abundant, chemically stable, and durable minerals in Earth's crust is quartz. Lithogenous sediment is composed of two deposits Neritic deposits (neritos = of the coast) are found on continental shelves and in shallow water near islands; these deposits are generally coarse grained. Alternatively, pelagic deposits (pelagios = of the sea) are found in the deep-ocean basins and are typically fine grained. Moreover, lithogenous sediment in the ocean is ubiquitous: At least a small percentage of lithogenous sediment is found nearly everywhere on the ocean floor.
How was the proto-Earth different from Earth today
its size was larger than today's Earth, and there were neither oceans nor any life on the planet. In addition, the structure of the deep proto-Earth is thought to have been homogenous (homo = alike, genous = producing), which means that it had a uniform composition throughout. The structure of proto-Earth changed, however, as its heavier constituents sank toward the center to form a heavy core.
Describe the process by which abyssal plains are created
Abyssal plains are formed by fine particles of sediment slowly drifting onto the deep-ocean floor.In addition, sediment traveling in turbidity currents from land adds to the sediment load.
Technically, what must a biogenies ooze contain to be classified as ooze? What other component do all oozes contain?
As its name implies, ooze resembles very fine-grained, mushy material. Technically, biogenous ooze must contain at least 30% biogenous test material by weight. What comprises the other part—up to 70%—of an ooze? Commonly, it is fine-grained lithogenous clay that is deposited along with biogenous tests in the deep ocean. By volume, much more microscopic ooze than macroscopic biogenous sediment exists on the ocean floor.
How is the age distribution pattern on the Hawaiian island-Emperor Seamount chain explained by the position of the Hawaiian hotspot? What could have caused the curious bend in the chain?
As the plate moved, it carried the active volcano off the hotspot, and a new volcano began forming, younger in age than the previous one. A chain of extinct volcanoes that is progressively older as one travels away from a hotspot is called a nematath (nema = thread, tath = dung or manure), or a hotspot track (see Figure 2.25). Moreover, recent plate reconstructions suggest that the observed bend in the Hawaiian-Emperor chain was created by a combination of the changing motion of the Pacific Plate (mainly as a result of changes in plate motions near Australia and Antarctica), the subduction of a plate in the northwest Pacific underneath Asia millions of years ago that altered the direction of mantle flow, and the slow movement of Hawaii's mantle plume itself.
What is bathymetry?
Bathymetry (bathos = depth, metry = measurement) is the measurement of ocean depths and the charting of the shape, or topography (topos = place, graphy = description of) of the ocean floor. Determining bathymetry involves measuring the vertical distance from the ocean surface down to the mountains, valleys, and plains of the sea floor.
What are the differences between a mid-ocean ridge and a hotspot?
Because of sea floor spreading, active volcanoes (seamounts) occur along the crest of the mid-ocean ridge. Some may be built up so high that they rise above sea level and become islands, at which point wave erosion becomes important. When sea floor spreading has moved the seamount off its source of magma (whether it is a mid-ocean ridge or a hotspot), the top of the seamount can be flattened by waves in just a few million years.
Describe the origin of Earth's oceans
Because outgassing releases mostly water vapor, this was the primary source of water on Earth, including supplying the oceans with water. Figure 1.25 shows that as Earth cooled, the water vapor released to the atmosphere during outgassing condensed, fell to Earth, and accumulated in low areas .Comets, which are composed of about half water, were once widely held to be the source of Earth's oceans. During Earth's early development, space debris left over from the origin of the solar system bombarded the young planet, and there could have been plenty of water supplied to Earth in this way.
Explain how submarine canyons are created
Canyons confined to the continental slope are straighter and have steeper canyon floor gradients than those that are cut into the continental shelf. These characteristics suggest the canyons are created on the continental slope by some marine process and enlarge into the continental shelf through time.
Describe the origin of hydrogenous sediment
Chemical reactions within seawater cause certain minerals to come out of solution, or precipitate (change from the dissolved to the solid state). Precipitation usually occurs when there is a change in conditions, such as a change in temperature or pressure or the addition of chemically active fluids.
Why is lithogenous sediment the most common neritic deposit? Why are biogenous ooze that most common pelagic deposits?
Coarse-grained lithogenous neritic deposits dominate continental margin areas (dark brown shading), which is not surprising because lithogenous sediment is derived from nearby continents. Pelagic deposits are dominated by biogenous calcareous oozes (blue shading), which are found on the relatively shallow deep-ocean areas along the mid-ocean ridge. Biogenous siliceous oozes are found beneath areas of unusually high biological productivity such as the northernmost North Pacific Ocean, surrounding Antarctica (green shading, where diatomaceous ooze occurs), and the equatorial Pacific (yellow shading, where radiolarian ooze occurs).
Describe the origin of Earth's atmosphere. How is the origin related to the origin of Earth's oceans?
Earth's initial atmosphere consisted of leftover gases from the nebula, but those particles were blown out to space by the Sun's solar wind. After that, a second atmosphere was most likely expelled from inside Earth by a process called outgassing. During the period of density stratification, the lowest-density material contained within Earth was composed of various gases. These gases rose to the surface and were expelled to form Earth's early atmosphere. Origin is related because of outgassing which produces mostly water vapor
What kind of unusual life can be found associated with hydrothermal vents? How do these organisms survive?
In addition, most hydrothermal vents foster unusual deep-ocean ecosystems that include organisms such as giant tubeworms, large clams, beds of mussels, and many other creatures—most of which were new to science when they were first encountered. These organisms are able to survive in the absence of sunlight because the vents discharge hydrogen sulfide gas, which is metabolized by archaeons and bacteria and provides a food source for other organisms in the community.
What is the difference between neritic and pelagic deposits? Give examples of lithogenous sediments found in each.
Lithogenous sediment is derived from rocks on nearby landmasses, consists of coarse-grained deposits, and accumulates rapidly on the continental shelf, slope, and rise. Examples of lithogenous neritic deposits include beach deposits, continental shelf deposits, turbidite deposits, and glacial deposits. Most pelagic deposits are composed of fine-grained material that accumulates slowly on the deep-ocean floor.Pelagic lithogenous sediment includes particles that have come from volcanic eruptions, windblown dust, and fine material that is carried by deep-ocean currents.
Describe what Earth's magnetic field looks like and how it has changed over time.
Magnetic bar that travels across the Earth with opposite polarities on each side of the bar. As time has passed the magnetic north switches to south and vice versa. Earth's rotation causes the electrically conducting liquid iron outer core to generate a self-sustaining magnetic field. Every so often, the flow of liquid iron is disturbed locally and twists part of the magnetic field in the opposite direction
Have the oceans always been salty? Why or why not?
No they have not because acidic rain dissolved minerals and volcanic gases dissolved and washed in the oceans making a chemical mixture that was salty.
What are some differences between a submarine canyon and an ocean trench
Ocean trenches are deep linear scars in the ocean floor, caused by the collision of two plates along convergent plate margins. The continental shelf exhibit submarine canyons, which are narrow but deep submarine valleys that are V-shaped in profile view and have branches or tributaries with steep to overhanging walls.
If siliceous ooze is slowly but constantly dissolving in seawater, how can deposits of siliceous ooze accumulate on the ocean floor?
One way is to accumulate the siliceous tests faster than seawater can dissolve them. For instance, many tests sinking at the same time will create a deposit of siliceous ooze on the sea floor below (Figure 4.13).7 Once buried beneath other siliceous tests, they are no longer exposed to the dissolving effects of seawater. Thus, siliceous ooze is commonly found in areas below surface waters with high biologic productivity of silica-secreting organisms.
How does the presence of oxygen in our atmosphere help reduce the amount of ultraviolet radiation that reaches Earth's surfaces?
Oxygen in the upper atmosphere make up the ozone that protects us from the ultraviolet radiation from the sun
Most lithospheric plates contain both oceanic ridges and oceanic rises. Use plate boundaries to explain why this is true.
Pull-apart faults located along the central rift valley show that the plates are continuously being pulled apart rather than being pushed apart by the upwelling of material beneath the mid-ocean ridge. Upwelling of magma beneath the mid-ocean ridge is simply filling in the void left by the separating plates of lithosphere.
Describe how the half-life of radioactive materials can be used to determine the age of a rock through radiometric age dating.
Radioactive materials have a characteristic half-life, which is the time required for one-half of the atoms in a sample to decay to other atoms. The older the rock is, the more radioactive material will have been converted to decay product. Analytical instruments can accurately measure the amount of radioactive material and the amount of resulting decay product in rocks
Describe characteristics and features of the mid-ocean ridge, including the differences between oceanic ridges and oceanic rises
Segments of the mid-ocean ridge called oceanic ridges have a prominent rift valley and steep, rugged slopes, and oceanic rises have slopes that are gentler and less rugged. As explained in Chapter 2, the differences in overall shape are caused by the fact that oceanic ridges (such as the Mid-Atlantic Ridge) spread more slowly than oceanic rises (such as the East Pacific Rise).
Explain the stages of progression that result in calcareous ooze existing below the CCD.
The mid-ocean ridge is a topographically highfeature that rises above the sea floor. It often pokes up above the CCD, even though the surrounding deep-ocean floor is below the CCD. Thus, calcareous ooze deposited on top of the mid-ocean ridge does not dissolve. However, sea floor spreading causes the newly created sea floor and the calcareous sediment on top of it to move into deeper water away from the ridge, eventually being transported below the CCD. This calcareous sediment will dissolve below the CCD unless it is covered by some deposit that is unaffected by the CCD (such as siliceous ooze or abyssal clay).
Explain what graded bedding is and how it forms
Stratification in which each layer displays a decrease in grain size from bottom to top. As the energy of the turbidity current dissipates, larger pieces settle first, then progressively smaller pieces settle, and eventually even very fine pieces settle out, which may occur weeks or months later.
Where is the deepest part of the ocean? How deep is it, and how does it compare to the height of the tallest mountain on Earth?
The deepest part of the ocean is the Mariana Trench in the Pacific Ocean. It is 11,022 meters (36,161 feet) deep The highest mountain in the world (the mountain with the greatest height above sea level) is Mount Everest in the Himalaya Mountains of Asia, at 8850 meters (29,035 feet). Even so, Mount Everest is a full 2172 meters (7126 feet) shorter than the Mariana Trench is deep
Describe the differences in earthquakes magnitudes that occur between the three types of plate boundaries and explain why these differences occur.
The forces involved in convergent-plate-boundary collisions are enormous. Huge lithospheric slabs of rock are relentlessly pushing against each other, and the subducting plate must actually bend as it dives below the surface. In addition, thick crust associated with convergent boundaries tends to store more energy than the thinner crust at divergent boundaries. Transform boundaries cause offsets which results in transform faults like San Andreas fault line which cuts through continental crust it creates more powerful earthquakes. The amount of energy released by earthquakes along divergent plate boundaries is closely related to the spreading rate. The faster the sea floor spreads, the less energy is released in each earthquake.
Describe the differences between oceanic ridges and rises.
The gently sloping and fast-spreading parts of the mid-ocean ridge are called oceanic rises. Conversely, steeper-sloping and slower-spreading areas of the mid-ocean ridge are called oceanic ridges
What are some differences between the lithosphere and the asthenosphere
The lithosphere is a relatively cool, rigid shell that includes all the crust and the topmost part of the mantle. lithosphere is further subdivided into oceanic crust and continental crust. The asthenosphere is a relatively hot, plastic region beneath the lithosphere. The asthenosphere can deform without fracturing if a force is applied slowly. This means that it has the ability to flow but has high viscosity (viscosus = sticky). Viscosity is a measure of a substance's resistance to flow.12 Studies indicate that the high-viscosity asthenosphere is flowing slowly through time; this has important implications for the movement of lithospheric plates.
Why is it so rare to find a pure marine sediment type? Give some examples of mixtures of sediment.
The ocean is a messy place. Lithogenous and biogenous sediment rarely occur as absolutely pure deposits that do not contain other types of sediment. As a result, most marine sediments occur as mixtures.Most calcareous oozes contain some siliceous material and vice versa. The composition of biogenous ooze includes up to 70% fine-grained lithogenous clays.
List the two major chemical compounds of which most biogenous sediment is composed and two examples of the microscopic organisms that produce them.
The two most common chemical compounds in biogenous sediment are calcium carbonate (CaCO3, which forms the mineral calcite) and silica. Most of the silica in biogenous ooze comes from microscopic algae called diatoms (diatoma = cut in half) and protozoans called radiolarians
How do fecal pellets help explain why the particles found in the ocean surface waters are closely reflected in the particle composition of the sediment directly beneath? Why is this unexpected?
These pellets are full of the remains of algae and protozoans from the surface waters (Figure 4.23) and, though still small, are large enough to sink to the deep-ocean floor in only 10 to 15 days. Once fecal pellets settle onto the ocean floor, the organic material in them is quickly consumed by bacteria and other microbes, releasing the indigestible, inorganic hard parts to the sediment. It is unexpected because the ocean current can carry these tests miles before they reach the deep ocean floor.
Convergent boundaries can be divided into three types, based on the types of crust contained on the two colliding plates. Compare and contrast the different types of convergent boundaries that result from these collisions
When an oceanic plate and a continental plate converge, the denser oceanic plate is subducted (Figure 2.20a). The oceanic plate becomes heated as it is subducted into the asthenosphere and releases superheated gases that partially melt the overlying mantle, which rises to the surface through the overriding continental plate. When two oceanic plates converge, the denser oceanic plate is subducted (Figure 2.20b). Typically, the older oceanic plate is denser because it has had more time to cool and contract.Similar to oceanic-continental convergence, the subducting oceanic plate becomes heated, releases superheated gases, and partially melts the overlying mantle. Continental lithosphere forms differently than oceanic lithosphere, however, and old continental lithosphere is no denser than young continental lithosphere. It turns out that neither subducts because they are both too low in density to be pulled very far down into the mantle. Instead, a tall uplifted mountain range is created by the collision of the two plates
Examine figures 2.31 and 2.33. In which ocean basin would you expect to find the oldest sea floor? Explain your reasoning.
You would find the oldest sea floor in the juvenile stage because that is when the continents are spreading creating divergent boundaries which make up sea floors with matching coasts
Discuss the origin of the solar system using nebular hypothesis
all bodies in the solar system formed from an enormous cloud composed mostly of hydrogen and helium, with only a small percentage of heavip elements. As this huge accumulation of gas and dust revolved around its center, it began to contract under its own gravity, becoming hotter and denser, eventually forming the Sun.
Why is most of lithogenous sediment composed of quartz grains? What is the chemical composition of quartz?
composed of silicon and oxygen in the form of SiO2. Because quartz is resistant to abrasion, it can be transported long distances and deposited far from its source area. The majority of lithogenous deposits—such as beach sands—are composed primarily of quartz
Describe the major features of a passive continental margin: continental shelf, continental slope, continental rise, submarine anyone, and deep seas fans
continental shelf- The continental shelf is defined as a generally flat zone extending from the shore beneath the ocean surface to a point at which a marked increase in slope angle occurs, called the shelf break continental slope- A relatively steeply sloping surface lying seaward of the continental shelf. continental rise- A gently sloping depositional surface at the base of the continental slope. submarine canyon- A steep, V-shaped canyon cut into the continental shelf or slope deep sea fans- A large fan-shaped deposit commonly found on the continental rise seaward of such sediment-laden rivers as the Amazon, Indus, or Ganges-Brahmaputra. Also known as a submarine fan.
Describe the origin of cosmogenous sediment
cosmogenous sediment consists of two main types: microscopic spherules and macroscopic meteor debris. The debris from meteors—called meteorite material—settles out around the impact site and is either composed of silicate rock material (called chondrites) or iron and nickel (called irons). Microscopic spherules are small globular masses. Some spherules are composed of silicate rock material and show evidence of being formed by extraterrestrial impact events on Earth or other planets that eject small molten pieces of crust into space. These tektites (tektos = molten) then rain down on Earth and can form tektite fields. Other spherules are composed mostly of iron and nickel (Figure 4.19), and these form in the asteroid belt between the orbits of Mars and Jupiter when asteroids collide.
Using table 4.1 list and describe the characteristics of the four main types of marine sediment
lithogenous- ediment composed of mineral grains derived from the weathering of rock material and transported to the ocean by various mechanisms of transport, including running water, gravity, the movement of ice, and wind. biogenous- Sediment containing material produced by plants or animals, such as coral reefs, shell fragments, and housings of diatoms, radiolarians, foraminifers, and coccolithophores; components can be either macroscopic or microscopic. hydrogenous- Sediment that forms from precipitation from ocean water or ion exchange between existing sediment and ocean water. Examples are manganese nodules, metal sulfides, and evaporites. cosmogenous- Sediment derived from outer space
Why does a map of worldwide earthquakes closely match the locations of worldwide plate boundaries
most large earthquakes occur along ocean trenches, reflecting the energy released during subduction. occur along the mid-ocean ridge, reflecting the energy released during sea floor spreading. Still others occur along major faults in the sea floor and on land, reflecting the energy released when moving plates contact other plates along their edges. This is because most earthquakes worldwide are created by plates interacting with each other at their margins
What types of past environmental conditions can be inferred by studying cores of sediment?
sea surface temperature, nutrient supply, abundance of marine life, atmospheric winds, ocean current patterns, volcanic eruptions, major extinction events, changes in Earth's climate, and the movement of tectonic plates
Discuss the origin of the various peaks of the abyssal plains: seamounts, table mounts, and abyssal hills
seamounts- An individual volcanic peak extending over 1000 meters (3300 feet) above the surrounding ocean floor. table mounts- A conical volcanic feature on the ocean floor resembling a seamount except that it has had its top truncated to a relatively flat surface. abyssal hills- A volcanic peak rising less than 1 kilometer (0.6 mile) above the ocean floor.
