Environmental Geology

What is a porphyry? What are phenocrysts? What does it imply about how the rock cooled?

Occasionally, a melt begins to crystallize slowly at depth, growing some large crystals, and then is subjected to rapid cooling (following a volcanic eruption, for instance). This results in coarse crystals in a fine-grained groundmass, a porphyry -Phenocrysts, of course, indicate a (porphyritic) volcanic rock.

what is carrying capacity?

The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water, and other necessities available in the environment.

What is the difference between regional and contact metamorphism?

When hot magma formed at depth rises to shallower levels in the crust, it heats the adjacent, cooler rocks, and they may be metamorphosed; this is contact metamorphism. Metamorphism can also result from the stresses and heating to which rocks are subject during mountain-building or plate-tectonic movement. Such metamorphism on a large scale, not localized around a magma body, is regional metamorphism.

What does an exponential growth curve look like? What is doubling time (size)?

-Exponential growth produces a J-shaped curve, while logistic growth produces an S-shaped curve. -Doubling time is the amount of time it takes for a given quantity to double in size or value at a constant growth rate

What is the difference between a plutonic and volcanic igneous rock with regard to i) their origin, ii) the size of their mineral grains, and iii) the rate at which they cooled from a liquid?

-The proportions and compositions of these constituent minerals may vary, but all granites show the coarse, interlocking crystals characteristic of a plutonic rock. -Lava is a common product of volcanic eruptions, and the term volcanic is given to an igneous rock formed at or close to the earth's surface. Magmas that crystallize very near the surface cool more rapidly. There is less time during crystallization for large crystals to form from the magma, so volcanic rocks are typically fine-grained, with most crystals too small to be distinguished with the naked eye.

What are the four most common chemical elements in the Earth? What are the four most common elements in the Earth's crust?

-These four are iron, oxygen, silicon and magnesium -Oxygen - 46.6% Oxygen is the most abundant element in the Earth's crust. ... Silicon - 27.7% Silicon is the second most common element present in the crust with an abundance of 276,900 ppm. ... Aluminum - 8.1% At 80,700 ppm, aluminum is the third most abundant element in Earth's crust. ... Iron - 5%

3. If the entirety of Earth's history were laid out in a 24-hour day, when does our species, Homo sapiens, arrive?

6 seconds

ionic bond

A chemical bond resulting from the attraction between oppositely charged ions.

covalent bond

A chemical bond that involves sharing a pair of electrons between atoms in a molecule

What is a fault? what is an earthquake?

A fault is a break in a body of rocks, an earthquake is formed when these faults can no longer retain their energy caused by stress, energy is released in the form of vibrations causing body and surface waves.

What is the definition of a metamorphic rock? (p. 36) What are the conditions under which metamorphism occurs?

A metamorphic rock is one that has formed from another, preexisting rock that was subjected to heat and/or pressure. Heat and pressure commonly cause the minerals in the rock to recrystallize.

What is the difference between a null hypothesis and an alternate hypothesis?

A null hypothesis is a hypothesis that says there is no statistical significance between the two variables. ... An alternative hypothesis is one that states there is a statistically significant relationship between two variables

Why is the age of the seafloor no older than 200 million years old, whereas continental crust has been discovered that is over 4 billion years in age?

Also during the 1950s, researchers learned how to accurately determine the age of certain rock types, such as basalts, by dating radioactive isotopes within the rock (also called radiometric dating, discussed in class and in Appendix A). As geologists examined basalts from the seafloor, they noted that basalts closest to the mid-ocean ridge were younger in age, while those further away from the MOR grew progressively older. To date, the oldest ocean-floor basalts are ~200 Ma.

mid-ocean ridge

An undersea mountain chain where the new ocean floor is produced; a divergent plate boundary. When two plates collide, the denser plate bends and slides under down the overriding plate, usually oceanic.

Isotope

Atoms of the same element that have different numbers of neutrons

Atoms

Building blocks of matter

Who was Alfred Wegener and what was continental drift?

Climatologist Alfred Wegener was struck not only by the matching coastlines but by geologic evidence from the continents. Continental rocks form under a wide range of conditions and yield varied kinds of information. The jigsaw-puzzle fit of South America and Africa suggests that they were once joined together and subsequently separated by continental drift. Montgomery, Carla. Environmental Geology (p. 43). McGraw-Hill Higher Education. Kindle Edition.

In reference to population growth, what is exponential growth?

Exponential growth takes place when a population's per capita growth rate stays the same, regardless of population size, making the population grow faster and faster as it gets larger.

What are ferromagnesian minerals? What are some common (well, common to geologists) examples?

Ferromagnesian is the general term used to describe those silicates—usually dark-colored (black, brown, or green)—that contain iron and/or magnesium, with or without additional elements.

What did Wegener name his supercontinent? About how long ago did it break up? What were the major continents that comprised it and how does that compare with the current continental arrangement of the present day?

He proposed that all the continental landmasses had once formed a single supercontinent, Pangaea (Greek for "all lands"), which had then split apart, the modern continents moving to their present positions via a process called continental drift. South America, Africa, Antartica, India and Australia.

What happens to the growth of a population as it reaches its carrying capacity?

In a population at its carrying capacity, there are as many organisms of that species as the habitat can support. ... If resources are being used faster than they are being replenished, then the species has exceeded its carrying capacity. If this occurs, the population will then decrease in size

What is the difference between a hypothesis and a theory?

In science, a theory is a tested, well-substantiated, unifying explanation for a set of verified, proven factors. A theory is always backed by evidence; a hypothesis is only a suggested possible outcome, and is testable and falsifiable. ... Scientific laws explain things, but they do not describe them.

Dip-Slip fault

Is the sinking and rising of the opposite sides of the fault. In a normal fault the hanging wall sinks, in a reverse fault the hanging wall rises.

What is the difference between magma and lava?

Magma is the name given to naturally occurring hot, molten rock material. A magma that flows out on the earth's surface while still wholly or partly molten is called lava.

What are sheet silicates (micas)?

Micas are sheet silicates, built on an atomic scale of stacked-up sheets of linked silicon and oxygen atoms. Because the bonds between sheets are relatively weak, the sheets can easily be broken apart

What are native elements? Provide an example

Native elements, as shown in table 2.2, are even simpler chemically than the other nonsilicates. Native elements are minerals that consist of a single chemical element, and the minerals' names are usually the same as the corresponding elements. Example: However, some of our most highly prized materials, such as gold, silver, and platinum, often occur as native elements.

Minerals five characteristics

Naturally ocurring, inorganic, chemical composition, solid, crystalline structure

What is the difference between geographic north and magnetic north? What specific layer within the Earth generates the Earth's magnetic field? What is magnetic declination?

Normal polarity: the northern magnetic pole (where a compass points to when pointing "north") lies near the north geographic pole (the axis around which the Earth spins). Rocks that crystallize when the Earth's magnetic field has a normal polarity are said to be normally magnetized. outer core reveal the orientation of the rock in three dimensions: the minerals in the rock point to the magnetic poles (declination)

What is a peridotite and where are they found?

Peridotite is a very dense, coarse-grained, olivine-rich, ultra-mafic intrusive rock. It is noted for its low silica content and contains very little or no feldspar ( orthoclase, plagioclase). It is a common component of the oceanic lithosphere and is derived from the upper mantle.

What is strain? What is the difference between elastic, plastic, and brittle deformation?

Strain is deformation resulting from stress. It may be either temporary or permanent, depending on the amount and type of stress and on the physical properties of the material. If elastic deformation occurs, the amount of deformation is proportional to the stress applied Once the elastic limit of a material is reached, the material may go through a phase of plastic deformation with increased stress In brittle materials, rupture may occur before there is any plastic deformation.

What are carbonate rocks? Provide an example. Where are they typically found / formed?

The carbonates all contain carbon and oxygen combined in the proportions of one atom of carbon to three atoms of oxygen (written CO3). The carbonate minerals all dissolve relatively easily, particularly in acids, and the oceans contain a great deal of dissolved carbonate. Example: Geologically, the most important, most abundant carbonate mineral is calcite, which is calcium carbonate. Precipitation of calcium carbonate from seawater is a major process by which marine rocks are formed

Is carrying capacity a fixed number? Why or why not?

The carrying capacity for any given area is not fixed.

nucleus of atom

The center of an atom that contains the protons and neutrons

What are the three differentiated layers of the Earth?

The core, mantle, and crust

What is the difference between fracture and cleavage

The difference between cleavage and fracture is that cleavage is the break of a crystal face where a new crystal face is formed where the mineral broke, whereas fracture is the "chipping" of a mineral.

The difference between a focus and epicenter

The focus is within the earths crust and is the origin of the earthquake, while the epicenter is the surface origin of the earthquake.

What are feldspars?

The most abundant group of minerals in the crust is a set of chemically similar minerals known collectively as the feldspars. They are composed of silicon, oxygen, aluminum, and either sodium, potassium, or calcium, or some combination of these three.

liquefaction

The process by which an earthquake's violent movement suddenly turns loose soil into liquid mud

Intra-plate earthquakes

These occur in the middle or interior of tectonic plates and are much rarer than boundary earthquakes

What is the concept behind paleomagnetism? What is a magnetic reversal? What is the Curie temperature? What is the mineral that makes rocks magnetic?

They retain their internal magnetic orientation unless they are heated again. This is the basis for the study of paleomagnetism, "fossil magnetism" in rocks. Today, the phenomenon of magnetic reversals is well documented. Rocks crystallizing at times when the earth's field was in the same orientation as it is at present are said to be normally magnetized; rocks crystallizing when the field was oriented the opposite way are described as reversely magnetized. As igneous rocks cool from a molten magma, the rocks cool below a specific temperature called the Curie temperature (named after Pierre Curie, who discovered this property in 1895); the temperature of the Curie point varies depending on the rock: for magnetite, the Curie point is 585°C (1085°F). The melting temperature of the magnetite is 1538°C (2800°F). As the rock cools below its Curie temperature, the rock's iron crystals align with the current orientation of the Earth's magnetic field mineral magnetite

What is the seafloor spreading hypothesis? Who proposed the idea? How does the discovery of magnetic stripes on the ocean floor tie in with support for plate tectonics?

Thus was born the concept of seafloor spreading, the parting of seafloor rocks at the ocean ridges. If the oceanic plates split and move apart, a rift begins to open, and mantle material from below can flow upward. proposed first by American geologist Harry Hess

Was Wegener's idea of continental drift accepted by the geologic community? Why or why not?

To a great many reputable scientists, these were insurmountable obstacles to accepting the idea of continental drift. As it turns out, additional relevant evidence was simply undiscovered or unrecognized at the time. Beginning in the 1960s (thirty years after Wegener's death), data of many different kinds began to accumulate that indicated that the continents have indeed moved. Continental "drift" turned out to be just one consequence of processes encompassed by the broader theory of plate tectonics.

What is a subduction zone?

Where one lithospheric plate is dragged or pushed below another lithospheric plate.

Porphyry

a hard igneous rock containing crystals, usually of feldspar, in a fine-grained, typically reddish groundmass.

strike fault

a type of fault where rocks on either side move past each other sideways with little up or down motion

flood basalt

huge amounts of lava that erupt from fissures

Mineral Properties

luster, streak, color, specific gravity, cleavage/fracture, hardness, magnetism, fluorescence

hot spots

places where molten material from the mantle reaches the lithosphere -hawaii, yellow stone

Ions

positively and negatively charged atoms

magnetic declination

the angle between geographic north and the north to which a compass needle points

thrust fault

the angle go the fault is at 30 degrees or less

atomic number

the number of protons in the nucleus of an atom

What is the asthenosphere? How does it differ from the lithosphere? (

the portion of the upper mantle that flows, this layer behaves "plastically". The asthenosphere liesdirectlyunderthelithosphere,andextendstoadepthof300km(200mi)intothemantle. Whilethe asthenosphere is mostly solid, its high temperatures and pressures allow the rocks within it to flow plastically under stress: grains of rock within the asthenosphere have "partially melted".

Magnitude of earthquake

the total amount of energy released during an earthquake. Richter scale developed by Charles Richter in 1935.

What is a lithospheric plate? What is a plate boundary? What are the three kinds of plate boundaries? What is the difference between the three different kinds of plate boundaries?

-A lithospheric plate are the large tectonic plates that create our oceans, continents, and mountain ranges. -Convergent, divergent, and transform boundaries are where the plates meet. Convergent - the plates come together Ocean-ocean: a plate of oceanic lithosphere collides with another plate of oceanic lithosphere2. Ocean-continent: a plate of oceanic lithosphere collides with a plate of continental lithosphere3. Continent-continent: a plate of continental lithosphere collides with another plate of continental lithosphere When two plates collide, the denser plate bends and slides under down the overriding plate, forming a subduction zone. Keep in mind the following: 1. Oceanic crust is composed of basalt, continental crust is composed of granite2. Basalt is a denser rock than granite (basalt is composed of denser elements than granite) 3. Thus, oceanic crust is denser (less buoyant) than continental crust. divergent - In divergent boundaries, or spreading centers, two plates move apart. Magma rises up from the mantle to fill in the space, often erupting out through volcanoes that form in divergent boundaries (earthquakes are also common here). As the magma cools, it forms new crust (the new crust can be either oceanic or continental, depending on where the spreading center has formed). Divergent boundaries in the ocean form mid-ocean ridges (MORs, described above). MORs line the ocean floor (and some continents) across the entire planet. transform - Mid-ocean ridges are not long, continuous, uninterrupted undersea volcanic mountain chains, but rather short segments that are appear to be offset by fracture zones. It was originally thought that the entire length of the fracture zone - which can extend miles beyond the width of the mid-ocean ridge, was made by a type of fault called a transform fault, but it was later discovered that only the area of the fracture zone within the mid-ocean ridge itself showed any earthquake activity (and hence, movement). The area where the active movement of the fracture zone occurs is called a transform fault: in a transform fault, two plates slide past one another in opposite directions (one plate moves left, the other right), in a shearing motion. As a result of this shearing motion, earthquakes - commonly associated with transform faults - can occur.

What is a rock? What are the three general categories of rock? Be familiar with the rock cycle.

-A rock is a solid, cohesive aggregate of one or more minerals, or mineral materials (for example, volcanic glass, discussed later). This means that a rock consists of many individual mineral grains (crystals)—not necessarily all of the same mineral— or crystals plus glass, which are firmly held together in a solid mass. -The three broad categories of rocks—igneous, sedimentary, and metamorphic—are distinguished by the processes of their formation. -The essence of the concept of the rock cycle, explored more fully at the end of this chapter, is that rocks, far from being the permanent objects we may imagine them to be, are continually being changed by geological processes. Over the vast span of geologic time, billions of years, a given bit of material may have been subject to many, many changes and may have been part of many different rocks.

How do sedimentary rocks form? What is the difference between physical and chemical weathering? What are the two general categories of sedimentary rock? Within each category, how are the rocks organized / classified? Know how the terms apply to sedimentary rock formation: compaction, cementation, and lithification?

-A sedimentary rock is formed from sediment, debris of preexisting rocks deposited at low temperatures at the earth's surface. -Sediments are loose, unconsolidated accumulations of mineral or rock particles that have been transported by wind, water, or ice, or shifted under the influence of gravity, and redeposited. -Clastic sedimentary rocks (from the Greek word klastos, meaning "broken") are formed from the products of the mechanical breakup of other rocks. --Chemical sedimentary rocks form not from mechanical breakup and transport of fragments, but from crystals formed by precipitation or growth from solution. -A common example is limestone, composed mostly of calcite (calcium carbonate). The chemical sediment that makes limestone may be deposited from fresh or saltwater; -When sediments are compacted or cemented together into a solid, cohesive mass, they become sedimentary rocks. -The set of processes by which sediments are transformed into rock is collectively described as lithification

What is the difference between a conglomerate, breccia, sandstone, and shale? (pp. 34-36) What is limestone? What is its chemical formula? How can it form? (List two methods) How does its formation differ from that of coal? (and what is coal?)

-Conglomerate (/kənˈɡlɒmərɪt/) is a coarse-grained clastic sedimentary rock that is composed of a substantial fraction of rounding to subangular gravel-size clasts, e.g., granules, pebbles, cobbles, and boulders, larger than 2 mm -A breccia does have angular fragments, but the fragments in a breccia are typically rock fragments, not individual mineral crystals.

What is the difference between an aphanitic and phaneritic texture? What is a peridotite and where are they found?

-IV. Aphanitic (grains too fine to distinguish easily with the naked eye). -Phaneritic (coarse enough that all grains are visible to the naked eye).

What are silicates? What is the general chemical formula of a silicate mineral? What is the most common silicate and what is its formula?

-Silicate group, all of which are compounds containing silicon and oxygen, and most of which contain other elements as well. -The basic building block of all silicates is a tetrahedral arrangement of four oxygen atoms (anions) around the much smaller silicon cation -Quartz is found in a variety of rocks and soils. Commercially, the most common use of pure quartz is in the manufacture of glass, which also consists mostly of silicon and oxygen.

What is each layer composed of? What is the difference in composition between the outer core and inner core?

-The most abundant elements in the Earth's crust include (listed here by weight percent) oxygen, silicon, aluminum, iron, and calcium. -The mantle is composed of silicate minerals that are similar to ones found in the crust, except with more magnesium and iron and less silicon and aluminum. -Both the inner and outer core is made up of mostly iron and a little bit of nickel

What is the difference between a basalt and a granite? A granite and a rhyolite?

-The most common volcanic rock is basalt, a dark rock rich in ferromagnesian minerals and feldspar (figure 2.11C). The ocean floor consists largely of basalt. Occasionally, a melt begins to crystallize slowly at depth, growing some large crystals, and then is subjected to rapid cooling -Compositionally, a typical granite consists principally of quartz and feldspars, and it usually contains some ferromagnesian minerals or other silicates. The proportions and compositions of these constituent minerals may vary, but all granites show the coarse, interlocking crystals characteristic of plutonic rock. Much of the mass of the continents consists of granite or of rock of granitic composition. -Rhyolite is the fine-grained, volcanic compositional equivalent of granite,

continental fissure eruptions

-pour out of cracks in lithosphere -result in large volume of "flood basalts"

Please be familiar with the following geographic features of the ocean floor (see also lecture notes, Ch. 3, p.2): a. Abyssal plainb. Mid-ocean ridge c. Deep-ocean trench

1. Abyssal plains: deep, wide, flat regions of the ocean floor that lay 4-5 km below sea level. 2. Mid-ocean ridges (MORs): many the abyssal plains were bisected by mid-ocean ridges (MORs): undersea volcanic mountain ranges that stretched for several thousand km, and whose peaks rose 2-2.5 km below sea level. A notable one was discovered running north-south in the middle of the Atlantic Ocean. MORs were noted for being roughly symmetrical: the profile on one side of the ridge was roughly a mirror image of the other. Perhaps most notable about MORs was that they all turned out to be linked across the globe and they were active both volcanically (erupting) and seismically (i.e. produced earthquakes). 3. Deep-ocean trenches: troughs that descended to depths > 8-10 km underwater were found along much of the perimeter of the Pacific Ocean (the deepest of one of these trenches, the Mariana Trench in the western Pacific Ocean near Guam, was found to be nearly 11 km in depth: by comparison, the world's tallest peak, Mt. Everest, is 9 km high). All undersea trenches appeared to run parallel to and near the coasts of land-based regions known for their volcanism. These regions are called volcanic arcs and they form chains of active volcanoes: some arcs form a chain of islands (such as the Aleutian Islands, off the Alaska Coast), while other arcs fringe the edge of continents (e.g., the Andes mountains of South America).

What were five different lines of evidence Wegener provided to show that the continents moved?

1. Coastlines. On appearance of their coastlines alone, many continents look like they could fit back together: e.g., South America and Africa. 2. Glacial activity. Wegener, who was a meteorologist, observed i) glacial striations (scratch marks left on rocks by glaciers) and ii) till deposits (till = rocks carried by the glacier and left behind after the glacier melted)...on sediments from southernmost South America, southern India, and southern Australia that all dated back to the late Paleozoic (~300 million years ago): even though South America, Australia and India currently reside nowhere near one another, nor are they close to the South Pole (from where the glaciers that left the striations would have originated). Wegener also noticed that the striations ran from the sea toward the continents: the opposite way in which modern glaciers move (glaciers form on land and flow to the sea). Wegener plotted the orientation of the striations and realized that i) the pattern would only make sense if the above continents were once all joined together (thus linking the glacier into a single continental ice sheet), and ii) part of Pangaea had to be at polar latitudes for the glacial ice sheet to develop in the first place. 3. Fossil evidence: plants. Wegener mapped the occurrences of three species of fossil plant (the most widely cited is the genus Glossopteris, an extinct fern) from the late Mesozoic (~100 Ma) and found that these fossils appeared over several - currently unconnected - southern continents. Wegener argued that the only way this could occur was if the continents were once all joined together: otherwise how could the plants have migrated across the sea? 4. Fossil evidence: animals. Wegener mapped the occurrences of various fossil animals, including a small, extinct, coastal marine reptile called Mesosaurus, and found a distribution similar to that of the plants mentioned above. 5. Rock assemblages. Wegener found similar assemblages of rock formations across different continents: e.g., he noticed that a band of Precambrian rocks (from 540 Ma) on the east coast of South America matched those on the west coast of Africa, two continents currently separated by an ocean. If the continents had once been together, these matching rock groups would have formed a continuous band of rock. Wegener proposed that not only did the coastlines of these continents match, but so also did their fossil and rock assemblages. An example cited by our textbook notes that the rocks that form the Appalachian Mountains of eastern North America can also be found in Greenland and the British Isles, where they form the Caledonian Range: this suggests that all three land masses (North America, Greenland, Britain) were once united as a single land mass in Earth history until thecontinents drifted apart ("Caledonia" = Latin name for Scotland).

What are convection cells and how do they play a role in plate tectonics? What is the difference between "slab-pull" and "ridge-push"

1. Convection cell model: hot mantle material rises up at spreading centers (MORs), then spreads outward, pulling along the overlying lithosphere with it. Once the mantle material cools, it sinks at subduction zones, pulling the overlying lithosphere with it. The mantle material then rises back up again at the spreading center, creating a circular convection cell (in a typical convection cell, warm fluids rise, cold fluids sink). 2. Slab-pull model: the weight of the dense, down-going slab of lithosphere in the subduction zone pulls the rest of the trailing plate along with it, further opening up the spreading center at the mid-ocean ridge. Recall that older oceanic lithosphere (> 10 Ma, e.g.) sinks due to its density. As it does so, it pulls the rest of the plate along behind it, like an anchor pulling an anchor line. 3. Ridge-push model As new lithosphere is created at mid-ocean ridges, the older material is pushed away from both sides of the mid- ocean ridge axis. MORs have a slope to them, and gravity is thought to play a role in pushing the older basaltic crust further away from the ridge.

What is the lithosphere? Is it the same thing as continental crust? What is the difference between oceanic and continental lithosphere?

1. Lithosphere: the lithosphere incorporates all of the crust and part of the upper mantle. The thickness of the lithosphere varies: a. The lithosphere is thin under the oceans, where it reaches a depth of ~50 km (30 mi). b. The lithosphere is thicker under the continents, where it reaches a depth of ~250 km (150 mi). Continental lithosphere is buoyant: it is too light to subduct.d. Oceanic lithosphere is not as buoyant as continental lithosphere. Oceanic lithosphere will eventually subduct. This is why there is no oceanic lithosphere on the surface of our planet older than ~200 Ma.

What is the difference between a foliated and non-foliated metamorphic rock? (pp. 36-39) What is foliation and how does it occur?

In a rock subjected to directed stress, minerals that form elongated or platy crystals may line up parallel to each other. The resultant texture is described as foliation, from the Latin for "leaf" I. Nonfoliated; compact texture with interlocking grains: identified by predominant mineral(s). Montgomery, Carla. Environmental Geology (p. B-4). McGraw-Hill Higher Education. Kindle Edition.

What is stress? What are the three main types?

is defined as a force acting on an object per unit area (the amount of force acting on a specific area of an object). If the object is deformed as a result of that stress, causing a change in the object's shape, the resulting deformation is called strain. Below are some of the ways that stress can act on a rock: 1. Compressive stress: when a rock is squeezed (like the walls of the Death Star trash compactor closing in on Luke, Leia, Han, and Chewbacca in Star Wars, Episode IV (1977), the rock shortens (or flattens) as a result. Geologically, this occurs when two tectonic plates collide (see below). 2. Tensile stress (extension): when a rock is stretched or pulled apart, tension is produced. Geologically, this occurs at mid-ocean ridges (a type of spreading center) as the oceanic crust is pulled apart. 3. Shear stress: when one part of the rock moves sideways past another across a plane, similar to how a deck of cards slide past one another when shuffled. Geologically, this occurs with transform (strike-slip) faults (see below).