Geology Final Exam (The Complete Collection)

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Everything. 924 Terms

ATMOSPHERE

a layer consisting of a mixture of gases called air, surrounds our planet. Balloons rise because the gas in them is less dense than air.

wind

the flow of air from one place to another.

weather

the physical conditions (the temperature, pressure, moisture content, and wind velocity and direction) of the atmosphere at a given time and location.

climate

the average weather conditions during the year.

components of air

completely dry air consists of 78% nitrogen and 21% oxygen. The remaining 1% includes several gases in trace amounts: carbon dioxide and methane - greenhouse gases which allow solar radiation from the Sun to pass through, but trap infrared radiation from the Earth's surface.

aerosols

in addition to gases, the air contains trace amounts of ___. These tiny particles of liquid or solid material are so small that they remain suspended in the air. Include tiny droplets of water and acid and microscopic particles of sea salt, volcanic ash, clay, soot, and pollen.

acid rain

Pollutants within the air include sulfate and nitrate molecules, which react with water to make a weak acid that then falls from the sky as ___ ___.

air pressure

the push that air can exert on its surroundings, and air density therefore increase toward the surface of the Earth.

adiabatic cooling

when air moves from a region of higher pressure to a region of lower pressure, without adding or subtracting heat, it expands. When this happens, the air temperature decreases. Such a process is called ____ ____; air cools at 6 to 10 degrees C per kilometer that it rises.

adiabatic heating

if air moves from a region of lower pressure to a region of higher pressure, without adding or subtracting heat, it contracts, and the air temperature increases.

relative humidity

ratio between the measured water content and the maximum possible amount of water the air could hold, expresses as a percentage. Warmer air can hold more water than colder air. Water content in the air makes it either saturated or unsaturated.

dewpoint temperature

the temperature at which air becomes saturated is called the ___ _____; dew forms when under-saturated air cools at night and becomes saturated, so that water condenses on surfaces.

pauses

elevations where temperatures stop decreasing and start increasing or vice versa are called ___. These separate the Earth's atmosphere into four layers: troposphere, stratosphere, mesosphere, and the thermosphere.

troposphere

the layer closest to Earth, where almost all weather occurs; the thinnest layer; the air in this layer is constantly under convection.

stratosphere

the layer of the atmosphere that contains the ozone layer; temperature increases as you go up; air within this layer does not convect and thus remains stable and stratified, heating in this layer happens because ozone absorbs solar radiation.

mesosphere

the layer of the atmosphere between the stratosphere and the thermosphere and in which temperature decreases as altitude increases; this layer does not absorb much solar energy and thus cools with increasing distance from the hotter stratosphere below.

thermosphere

The uppermost layer of the atmosphere, in which temperature increases as altitude increases because gases of the thermosphere absorb short-wavelength solar energy; contains very little of the atmosphere's gas (less than 1%).

ionosphere

the layer of the atmosphere between 60 and 400 km, thus includes most of the mesosphere and the lower part of the thermosphere. In this layer, short-wavelength solar energy strips nitrogen molecules and oxygen atoms of their electrons and transforms them into positive ions. Plays an important role in modern communication.

isobar

a line on a map along which the air has a specified pressure is called an ___. In other words, the pressure is the same all along an these.

insolation

because the Earth is a sphere, not all areas receive the same amount of incoming solar energy, or ____: portions of the Earth's surface hit by direct rays of the Sun receive more energy per square meter than portions hit by oblique rays.

divergence zone

when the sinking air reaches low elevations, it divides, some moving back toward the equator near the surface and some moving north near the surface. A place where sinking air separates into flows moving in opposite directions is a ____ ___.

convergence zone

a place where two surface air flows meet so that air has to rise is called a _____ ___. This zone at latitude 60 deg. is called the 'polar front'

polar cells

where polar air sinks and flows away from the poles downward meeting the mid-latitude 'ferrel' cells at 60 degrees latitude.

prevailing winds

winds that blow in the same direction over large areas of Earth.

trade winds

Prevailing winds that blow northeast from 30 degrees north latitude to the equator and that blow southeast from 30 degrees south latitude to the equator.

doldrums

a belt of calms and light winds between the northern and southern trade winds of the Atlantic and Pacific, because air is mostly rising winds along the equator are very slow.

jet streams

because of the steepness of the gradient, high-altitude westerlies flow particularly fast. These zones of rapid movement, where winds typically flow at speeds of between 200 and 400 km per hour, are called __ ___.

weather system

a specific set of weather conditions, reflecting the configuration of air movement in the atmosphere, that affects a region for a period of time is called a ___ ___. They can move across the surface of the Earth, carried by prevailing winds.

air mass

a body of air, at least 1500 km across, that has recognizable physical characteristics is called an __ __. They move within the overall global circulation of the atmosphere, and their paths are controlled by prevailing winds.

front

the boundary between two air masses is called a ___. Three kinds: "cold", "warm", and "occluded".

wave cyclone

traveling cyclone of midlatitudes involving interaction of cold and warm air masses along sharply defined fronts.

fog

clouds that form at ground level make up __. Because clouds reflect and scatter incoming sunlight, they keep the ground cooler during the day, but at night they prevent infrared radiation from escaping, and thus keep the ground warmer.

condensation nuclei

droplets or ice grains clouds from by condensation or precipitation, respectively, when the air becomes saturated with water vapor. During cloud formation, water condenses on ______ ____, preexisting solid or liquid aerosols. Air can become saturated when evaporation provides additional water or when the air cools so that its capacity to hold water decreases.

lifting mechanisms

meteorologists recognize several conditions that cause air to rise: convective lifting, frontal lifting, covergence lifting, and orthographic lifting.

collision and coalescence

rain, snow, and sleet precipitate from clouds in two ways, depending on the temperature of the cloud. In warm clouds, rain develops by this process, during which the tiny droplets that compose the cloud collide and stick together to create a larger drop.

Bergeron process

precipitation involving the growth of ice crystals in a cloud at the expense of water droplets, is called the ___ ___.

cloud shapes

cumulus - puffy, cotton-ball-shaped; stratus - occur in relatively thin, stable layers, have a sheet/layered shape; cirrus - wispy shape, tapered feather-like curls.

storm

an episode of severe weather, when winds, rainfall, snowfall, and lightning become strong enough to be bothersome and/or dangerous. Form where large pressure gradients develop, producing strong winds.

hail

if updrafts in the cloud are strong enough, ice crystallizes in the higher levels of the cloud, where temperatures are below freezing, building into ice balls known as __.

lightning flash

air is a good insulator, so the charge separation can become very large until a giant spark or pulse of current jumps across the gap. We hear thunder that accompanies lightning because the immense energy of a flash almost instantaneously heats the surrounding air causing an explosion-like effect.

tornado and hurricane

a localized and violently destructive windstorm occurring over land characterized by a funnel-shaped cloud extending toward the ground; a huge, rotating storm, resembling a giant spiral in which sustained winds are greater than 119 km. Within these formations, air pressure becomes much lower because of the upward flow of air.

isotherms

lines that connect points that have the same temperature.

orographic barrier

a landform (such as a mountain range) that diverts airflow upward or laterally. This diversion affects the amount of precipitation and wind a region receives.

monsoon

a major reversal in the wind direction that causes a shift from a very dry season to a very rainy season. In southern Asia, people depend on these rains to bring moisture for their crops.

El Nino

(oceanography) a warm ocean current that flows along the equator from the date line and south off the coast of Ecuador at Christmas time.

southern oscillation

the atmospheric pressure conditions corresponding to the periodic warming of El Nino and cooling of La Nina.

DESERT

a region that is so arid (dry) that it contains no permanent streams, except for rivers that bring water in from temperate regions elsewhere, and supports vegetation on no more than 15% of its surface. In general, desert conditions exist where less than 25 cm of rain falls per year, on average.

subtropical deserts

types of deserts; from because of the pattern of convection cells in the atmosphere. Low latitude deserts, in the vicinities of the Tropics of Cancer and Capricorn, areas of high pressure and sinking air that is compressed and warmed.

rain shadow deserts

types of deserts; as air flows over the sea toward a coastal mountain range, the air must rise, expand and cool. The water it contains condenses and falls as rain on the seaward flank of the mountains, nourishing a coastal rain forest. As a consequence, this shadow forms, and the land beneath it becomes a desert.

desert varnish

a dark, rusty brown coating of iron oxide, manganese oxide, and clay covering the surface of many rock varieties in deserts.

arroyos (dry washes)

flash floods carve steep-sided channels into the ground. Scouring of bedrock walls by sand-laden water may polish the walls and create grooves. Dry stream channels in desert regions of the Western United States are called ____, and in the Middle East/North Africa they are called wadis.

suspended load

wind, just like flowing water, can carry sediment both as suspended load and as bed load; this load, with fine-grained sediment such as dust and silt held in suspension, floats in the air and moves with it.

saltation

moderate to strong winds can roll and bounce sand grains along the ground, a process called ____. This constitutes the wind's surface load, process begins when turbulence caused by wind shearing along the ground surface lifts sand grains.

lag deposit

in some cases, wind carries away so much fine sediment that pebbles and cobbles become concentrated at the ground surface. An accumulation of coarser sediment left behind when fine-grained sediment blows away is called __ ____.

desert pavement

in many locations, the desert surface resembles a tile mosaic in that it consists of separate stones that fit together tightly, forming a fairly smooth surface layer above a soil composed of silt and clay. Such natural mosaics constitute ___ ____.

ventifacts

rocks whose surface has been faceted by the wind are faceted rocks, or ____. Wind abrasion also gradually polishes and bevels down irregularities on a desert pavement and polishes the surfaces of desert-varnished outcrops, giving them a reflective sheen.

yardangs

in places where a resistant layer of rock overlies a softer layer of rock, wind abrasion may create a formation consisting of a resistant block perched on an eroding mushroom-like column of softer rock. These unusual features are called ____.

deflation

the process of lowering the land surface by wind erosion is called ____.

talus apron

under the influence of gravity, the resulting debris tumbles downslope and accumulates as a ___ ___ at the base of a hill. Typically see them fringing the bases of cliffs in deserts.

alluvial fan

the fan of distributaries spreads sediment, or alluvium, out into a broad ___ __, a wedge-shaped pile of sediment. These emerging from adjacent valleys may merge and overlap along the front of a mountain range, creating an elongate wedge of sediment called a bajada.

interior basin

where sufficient water flows into a desert basin, it creates a permanent lake. If the basin is an ___ ___, with no outlet to the sea, the lake becomes very salty, because although its water escapes by evaporation in the desert sun, its salt cannot.

playa

during drier times, desert lakes evaporate entirely, leaving behind a dry, flat lake bed known as a ___. Over time, a smooth crust of clay and various salts accumulates on the surface of these.

loess

much of the dust carried by desert wind is take out of the desert to accumulate elsewhere, forming layers of fine-grained sediment called ___.

dunes

sand being carried by desert wind, cannot travel far, and accumulates within the desert in piles called ___.

cliff retreat

in hilly regions, the lack of soil exposes rocky ridges and cliffs, cliffs erode when rocks split away along vertical joints. When this happens, the cliff face retreats but retains roughly the same form, the process, referred to as ___ ___, occurs in fits and starts.

cuestas

in places where bedding dips at an angle to horizontal, flat-topped mesas and buttes don't form; rather, asymmetrical ridges called ___ develop.

inselberg

with progressive cliff retreat on all sides of a hill, finally all that remains of the hill is this relatively small island of rock, surrounded by alluvium-filled basins.

pediments

bedrock surfaces extended outward like ramps from the steep cliffs of a mountain range on one side, to alluvium-filled valleys on the other. These are consequences of erosion, left behind as a mountain front gradually retreats.

sand dune

a pile of sand deposited by a moving current, form because of the wind in the desert. They start to form where sand becomes trapped on the windward side of an obstacle, such as a rock or a shrub. Types: barchan, transverse, longitudinal, parabolic, and star.

succulents

many desert plants have thick, fleshy stems and leaves. These plants are known as ____, can store water for long periods of time. Develop threatening needles or spines

desertification

the process of transforming nondesert areas to desert, has accelerated in modern times.

GLACIERS

slowly flowing masses of ice that survive the summer melt.

erratics

large boulders that have been transported into an area by a glacier.

ice age

Period of time when huge sheets of ice covered much of the earth's land, formed from ocean water, leaving ocean levels lower than they are now which exposed dry land that connected the continents.

mountain glaciers

accumulated snow at colder HIGHER elevations, snow turns to ice and flows to lower elevations where it melts.

cirques

bowl-shaped depressions on the flank of a mountain; valley glaciers, rivers of ice that flow down valleys.

continental glaciers

vast ice sheets that spread over thousands of square kilometers of continental crust.

temperate glaciers

glaciers occurring in regions where atmospheric temperatures become high enough during a substantial portion of the year for the glacial ice to be at or near its melting temperature throughout much of the year.

polar glaciers

occur in regions where atmospheric temperatures stay so low all year long that the glacial ice remains well below melting temperature throughout the entire year.

formation of glaciers

in order for glacial ice to form - the local climate must be sufficiently cold, must be sufficient snowfall for a large amount to accumulate, and the slope of the surface on which the snow accumulates must be gentle enough that the snow does not slide away in avalanches.

sublimate

the process of snow flakes evaporating directly into vapor, packs the snow more tightly as a result. As snow becomes buried, the weight of the overlying snow increases pressure, which causes remaining points of contact between snowflakes to melt. This process of melting at points of contact where the pressure is greatest is another example of pressure solution. Gradually, the snow transforms into a packed granular material called firn.

wet-bottom glaciers

glaciers move when meltwater accumulates at their bases, so that the mass of the glacier slides partially on a layer of water or on a slurry of water and sediment. Known as basal sliding, the water or wet slurry holds the glacier above the underlying rock and reduces friction between the glacier and its substrate. Is the dominant style of movement for these glaciers.

ice quakes

basal sliding motions of glaciers occur episodically - the ice stays fixed for a while until stress builds up sufficiently to cause the ice to lurch forward suddenly. This "stick-slip" generates __ ___.

dry-bottom glaciers

glaciers which move by means of internal flow, during which the mass of ice slowly changes shape internally without breaking apart or completely melting. Ice deforms plastically and the crystals slide past each other. These glaciers are so cold that their base remains frozen to their substrate.

crevasse

a large crack that develops by brittle deformation in a glacier is called a ___.

surge

if water builds up beneath a valley glacier to the point where if lifts the glacier off its substrate, the glacier undergoes a ___ and flows much faster for a limited time, until the water escapes.

ablation

the removal of ice by sublimation (the evaporation of ice into water vapor), melting, and calving (the breaking off of chunks of ice at the edge of the glacier) - subtracts from the account.

zone of accumulation and ablation

snowfall adds to the glacier in the zone of ___, whereas ablation subtracts in the zone of ___; the boundary between these two zones is the equilibrium line.

glacial advance

the leading edge or margin of a glacier is called its toe, or terminus. If the rate at which ice builds up in the zone of accumulation exceeds the rate at which ablation occurs below the equilibrium line, then the toe moves forward into previously unglaciated regions. Such a change is called a ___ ___.

glacial retreat

if the rate of ablation exceeds the rate of accumulation, then the position of the toe moves back toward the origin of the glacier; such a change is called a ___ ___. The position of the toe moves upslope.

ice shelves

continental glaciers entering the sea become broad, flat sheets called __ ____.

iceberg

if a free-floating chunk rises 6 m above the water and is at least 15 m long, it is formally called an ___.

drop stones

larger rocks that drop from the ice to the sea floor are called __ ___. In ancient glacial deposits, these appear as isolated blocks surrounded by mud.

glacially polished surfaces

a polished rock surface created by the glacial abrasion of the underlying substrate.

glacial striations

scratches and grooves on bedrock caused by glacial abrasion.

hanging valleys

shallow glacial valleys that met up with deep valleys.

fjords

the floors of valleys cut by coastal glaciers during the last ice age were cut much deeper than present sea level.

moraine

A ridge formed by the till deposited at the edge of a glacier. Unsorted material deposited along the sides of a valley glacier. If flowing water runs along the edge of the glacier and sorts the sediment of a lateral ____, a stratified sequence of sediment, called a kame, forms.

glacial drift

several different types of sediment can be deposited in glacial environments; types: glacial till, erratics, glacial marine, glacial outwash, glacial lake-bed sediment, loess.

loess

a fine-grained unstratified accumulation of clay and silt deposited by the wind.

glacial subsidence

the sinking of the surface of a continent caused by the weight of an overlying glacial ice sheet.

glacial rebound

the process by which the surface of a continent rises back up after an overlying continental ice sheet melts away and the weight of the ice is removed.

pluvial lakes

lakes that occur due to runoff accumulation from rainfall that does not evaporate.

permafrost

layer of permanently frozen subsoil in the tundra.

patterned ground

as a consequence of the freeze-thaw process, the ground splits into pentagonal or hexagonal shapes, creating a landscape called ___ ___. Water fills the gaps between the cracks and freezes to create wedge-shaped walls of ice.

glaciations

times during which the glaciers grew and covered substantial areas of the continents are called glacial periods, or ____, and times between glacial periods are called interglacial periods, or interglacials.

tillites

within the stratigraphic record, there are glacial deposits that have hardened into the rock. These deposits, called ____, consist of larger clasts distributed throughout a matrix of sandstone and mudstone. In many cases, these are deposited on glacially polished surfaces.

GLOBAL CHANGE

the transformations or modifications of both physical and biological components of the Earth System over time. There is gradual change over geologic time and catastrophic change which takes place relatively quickly. Unidirectional change involves transformations that never repeat, and cyclic change repeats the same steps over and over, though not necessarily with the same results.

biogeochemical cycle

the exchange of chemicals among living and nonliving reservoirs; some kinds of global change are due to changes in the proportions of chemical held in different reservoirs through time. Nonliving reservoirs include: the atmosphere, crust, and the ocean. Living reservoirs include: plants, animals, and microbes. The main two chemicals that are involved in this cycle are water and carbon.

global climate change

the transformations or modifications in Earth's climate over time, as well as the anthropogenic (human-caused) contributions over to global change.

supercontinent cycle

the process of change during which supercontinents form and later break apart. Geologists have found evidence that at least three or four times during the past 3 billion years of Earth history, supercontinents existed.

sedimentary sequence

throughout geologic time, when sea level rises the shoreline migrates inland and low-lying plains in the continents become submerged. During periods of particularly high sea level, more than half of the Earth's continental area can be covered by shallow seas; at such times, sediment buries continental regions, thereby changing their surface. When sea level falls, the continents become dry again, and regional unconformities develop - this blanket of sediment is called a ____ ____.

steady-state condition

for certain intervals of time, biogeochemical cycles attain a ___-___ _____, meaning that the proportions of a chemical in different reservoirs remain fairly constant even though there is a constant flux (flow) of the chemical among reservoirs.

global warming

if the average atmospheric and sea-surface temperature rises, we have ____ ____. Some changes are great enough to cause oceanic islands and large regions of continents to be submerged by shallow seas or to be covered by ice, whereas others are subtle, creating only a slight latitudinal shift in vegetation belts and a sea-level change measured in meters or less.

climate-change models

these provide insight into when and why climate changes took place in the past and whether they will happen in the future. Two basic approaches: researchers measure past climate change, indicated by the stratigraphic record, to document the magnitude of change that is possible and the rate at which such change occurred; also researchers develop computer programs to calculate how factors such as atmospheric composition, topography, ocean currents, and Earth's orbit affect the climate.

paleo-climate

past climate; these features can help to define these past climates: the stratigraphic record, paleontological evidence, oxygen-isotope ratios, bubbles in ice, growth rings, and human history.

greenhouse periods

geologists have reconstructed an approximate record of global climate, represented by mean temperature and rainfall, for geologic time. The record shows that at some times in the past, Earth's atmosphere was significantly warmer than it is today (____ ___); whereas at other times it was significantly cooler (ice ages).

causes of global climate change

What caused long-term global climate change? The answer probably lies in the complex relationships among the various geologic and biogeochemical cycles of the Earth system: positions of continents, volcanic activity, the uplift of land surfaces, formation of coal, oil, or organic shale, and life evolution.

runaway greenhouse effect

-occurs on Venus
-Venus is too close to the Sun to have liquid water oceans. Without water to dissolve CO2, it just gathers in the atmosphere.

factors of short-term climate change

fluctuations in solar radiation and cosmic rays - the amount of energy produced by the Sun varies with the sunspot cycle, changes in Earth's orbit and tilt, changes in volcanic emissions, changes in ocean currents, changes in surface albedo (reflectivity), and abrupt changes in concentrations of greenhouse gases.

mass-extinction events

the stratigraphic record shows that Earth history includes several of these - when large numbers of species abruptly vanish.

ecosystem

an interconnected network of organisms and the physical envrionment in which they live, is a product of evolution for an extended period of time.

ozone hole

an area of the ozone layer (near the poles) that is seasonally depleted of ozone. When emitted into the atmosphere, human-produced chemicals, most notably chlorofluorocarbons (CFCs), react with ozone in the stratosphere.

sustainable growth

an ability to prosper within the constraints of the Earth system - Economic growth and development that meets present needs without harming the needs of future generations.

ENERGY

provides the capacity to do work, to cause something to happen, or to cause change in a system.

energy resources

any item that can be employed for a useful purpose, more specifically something that can be used to produce heat, power muscles, produce electricity, or move vehicles.

fossil fuels (fuel)

(oil, gas, and coal) - combustible materials derived from organisms that lived in the past. Specifically they are matter that stores energy in a readily usable form.

sources of energy on Earth

(1) energy generated by nuclear fusion in the Sun and transported to Earth via electromagnetic radiation; (2) energy generated by the pull of gravity; (3) energy generated by nuclear fission reaction; (4) energy that has been stored in the interior of the Earth since the planet's beginning; (5) energy stored in the chemical bonds of compounds.

energy from the Sun

source of energy on Earth; (solar energy) can be converted directly to electricity, using solar panels, or it may used as heat water or to warm a house.

energy from gravity

source of energy on Earth; the gravitational attraction of the Moon, and the Sun, causes ocean tides of the sea surface. The flow of water in and out of channels during tidal changes can drive turbines.

both solar energy and gravity

source of energy on Earth; solar radiation heats the air, which becomes buoyant and rises. Thus, gravity causes cooler air to sink, the resulting air movement, wind, can power sails and windmills. When water condenses, it rains and falls on the land, where it accumulates in streams that flow downhill in response to gravity. This moving water powers waterwheels and turbines.

energy via photosynthesis

source of energy on Earth; green plants absorb some of the solar energy that reaches Earth's surface. With the aid of chlorophyll, plants produce sugar through a chemical reaction called photosynthesis. Burning plant matter in a fire releases potential energy stored in the chemical bonds of organic chemicals. Wood burning produces energy, and recently plant material (biomass) from crops such as corn and sugar cane has been used to produce ethanol, a flammable alcohol.

energy from chemical reactions

source of energy on Earth; a number of inorganic chemicals can burn to produce light and energy, energy resulting from exothermic reactions. Researchers have been studying electrochemical devices, such as hydrogen fuel cells, that produce electricity directly from these reactions.

energy from fossil fuels

source of energy on Earth; oil, gas, and coal come from organisms that lived long ago, and thus store solar energy that reached the Earth long ago. Burning these fuels produces energy in the same way that burning plant matter does.

energy from nuclear fission

source of energy on Earth; atoms of radioactive elements can split into smaller pieces. During this process, a tiny amount of mass is transformed into a large amount of energy, called nuclear energy. This type of energy runs nuclear power plants and nuclear submarines.

energy from Earth's internal heat

source of energy on Earth; Earth's internal energy dating back to the birth of the planet, while some is produced by radioactive decay in minerals. This internal energy heats water underground, the resulting hot water when transformed to steam, provides geothermal energy that can drive turbines.

hydrocarbons

oil and natural gas consist of these chainlike or ringlike molecules made of carbon and hydrogen atoms. These are considered to be a type of organic chemical, so named because similar chemicals make up living organisms. Products composed of short chains of molecules tend to be less viscous (they can flow more easily) and more volatile (they evaporate more easily) than products composed of long chains. Thus, short-chain molecules occur in gaseous form at room temperature, moderate-length-chain molecules as liquids, and long-chain molecules occur in solid form as tar.

oil and gas formations

the primary sources of the organic chemicals in oil and gas are dead algae and plankton. When algae and plankton die, they settle to the bottom of a lake or sea. Because their cells are so tiny, they can be deposited only in quiet-water environments in which clay also settles, so typically the cells mix with clay to create an organic-rich, muddy ooze; to be preserved it must be deposited in oxygen-poor water. Eventually, the resulting ooze lithifies and becomes black organic shale which contains raw materials from which hydrocarbons eventually form.

source rock

organic shale is referred to as ____ ___. Contains the raw materials from which hydrocarbons eventually form. These rocks are always sedimentary.

kerogen

if organic shale is buried deep enough (2 to 4 km), it becomes warmer, since temperature increases with depth in the Earth. Chemical reactions slowly transform the organic material in the shale into these waxy molecules called ___. Shale containing this is called oil shale.

oil window

if oil shale warms to temperatures of greater than about 90C, the kerogen molecules break down to form oil and natural gas molecules. At temperatures over 160C, any remaining oil breaks down to from natural gas, and at temperatures over 250C, organic matter transforms into graphite. Thus, oil itself forms only in this narrow range of temperatures. For regions with a geothermal gradient of 25C/km, this window lies at depths of about 3.5 km to 6.5 km, whereas gas can survive down to 9 km. Thus, hydrocarbon reserves can only exist in the topmost 15 to 25% of the crust.

hydrocarbon reserve

a known supply of oil and gas held underground. Currently countries bordering the Persian Gulf contain the world's largest reserves.

hydrocarbon system

a particular association of - source rock, reservoir rock, migratory pathway, and a trap - along with the processes of hydrocarbon generation, migration, and accumulation that ultimately produce a reserve from a given source, a system called the ____ ___.

hydrocarbon generation

geologists refer to the organic-rich shale as a source rock because it is the source for the organic chemicals that ultimately become oil and gas. If black shale resides in the oil window, the organic material within transforms into kerogen, and then into soil and gas. This process is ..

reservoir rocks

any organic matter in an oil shale remains trapped among the grains and can't move easily. Thus to obtain oil, companies drill into these rocks which contain (or could contain) an abundant amount of easily accessible oil and gas, meaning hydrocarbons that can be extracted out of the ground. Rocks with high porosity and permeability are the best.

pores

to be a reservoir rock, a body of rock must have space in which the oil or gas can reside, and must have channels through which the oil or gas can move. The space can be in the form of open spaces, or ___, between clastic grains or in the form of cracks and fractures that developed after the rock formed.

porosity

in some cases, groundwater passing through rock dissolves minerals and creates space, this refers to the amount of open space in a rock.

permeability

refers to the degree to which pore spaces connect to each other. In a permeable rock, the holes and cracks (pores) are linked, so a fluid is able to flow slowly through the rock, following a tortuous pathway.

migration pathway

to fill the pores of a reservoir rock, oil and gas must first migrate (move) from the source rock into a reservoir rock, which they will do over millions of years of geologic time. Hydrocarbons migrate because oil and gas are less dense than water, so they try to rise toward the Earth's surface to get above groundwater. Natural gas, being less dense, ends up floating above oil, thus buoyancy drives oil and gas upward. Typically, a hydrocarbon system must have a good ___ ___, such as a set of permeable fractures, in order for large volumes of hydrocarbons to move.

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