geo 303 exam 3

how to find age of sample

# of half-lives X length of half-life = age of sample

proterozoic

1st life, 2.5-.540 Ga saw the unfamiliar Archean world transition to an Earth like the one we know today. Lasting nearly 2 billion years (2 Ga) the Proterozoic is almost half of Earth history. There were fewer, larger lithospheric plates and larger continental landmasses. An oxygenated atmosphere changed the planet.

Cenozoic

65 ma- present, age of mammals, uplift of earths highest mountain ranges

The source of oil: Plankton

: It may come as a surprise but most of the world's oil and gas is made up of the fossil remains of microscopic marine plants and animals. That's why oil and gas are often referred to as a fossil fuel. One of the most important group of plankton involved in the formation of oil and gas are single-celled marine 'plants' called dinoflagellates, though many types of animal plankton are also important. Some oil and gas may have also originated from the remains of land plants, but we will not discuss these types of deposits in this talk.

Silurian and Devonian

A Late Devonian fossil skeleton of Tiktaalik; this lobe-finned fish was one of the first animals to walk on land. At the end of the Devonian, the first amphibians appeared on land, walking on legs and breathing with lungs. A fossil that was transitional between fish and amphibians was discovered in 1996. Tiktaalik was a lobe-finned fish that could do push-ups and look around on a swivel-jointed neck.

isotope

A chemical element is defined by the number of protons in the nucleus. By definition, hydrogen has 1 proton, helium has 2 protons, and so on through the periodic table of the elements. An isotope of an element refers to a proton-neutron combination. Example: the nucleus of the element lead (Pb) by definition contains 82 protons. If the nucleus contains 124 neutrons, the isotope is 206Pb, pronounced "lead-206." If the nucleus contains 125 neutrons, the isotope is 207Pb.

Disconformity

A disconformity is an unconformity within sedimentary layers due to an interruption in sedimentation. Disconformities are often subtle.

nonconformity

A nonconformity is an unconformity where igneous or metamorphic rocks are capped by sedimentary rocks. Crystalline igneous or metamorphic rocks were exposed by erosion. After a renewed marine invasion, sediment was deposited on this eroded surface.

Drilling the well

A potential oil trap is called a Prospect. Once a prospect has been identified, the next stage is to drill a hole into the top of the trap to see if it contains oil and gas. It is incredibly expensive to a drill hole. On an offshore rig is may cost $10,000 for every metre drilled. So if you are going to drill a hole 5000 metres underground it's going to cost you 20 million pounds/ 25 million dollars! Consequently geologists have to be pretty confident that they going to hit oil. If they drill too many 'dry holes' they will soon lose their jobs!

So... what things do we need to know to date something?

A.The half life (element dependent - known) B.# of half lives decayed t1/2 x # = age

Uncomformities

An unconformity is a time gap in the rock record, from nondeposition or erosion. There are three types of unconformity: an angular unconformity, a nonconformity, and a disconformity.

maturation of black shale

As more sediment accumulates on top, layers of Black Shale become buried more and more deeply in the Earth's crust. As they do so, they slowly heat up because of the geothermal gradient. With progressive heating the organic material in the plankton undergoes chemical and physical changes. It gradually breaks down into smaller and smaller hydrocarbons. At temperatures of around 30°C, a solid, sticky bitumen is produced. Around 90°C liquid oil is formed. As temperatures reach 150°C, natural gases like methane are given off. A Black Shale that is heated and gives off oil and gas is known in the oil industry as a Source Rock.

At the refinery

At the refinery, the crude oil, which also contains a lot of gas, is processed. This involves separating out all the different hydrocarbons in the crude oil. To do this, the crude oil is heated in a furnace and then passed through a cooling tower. The method relies on the fact that different hydrocarbons have different boiling points. Consequently the heavy hydrocarbons like bitumen with high boiling points accumulate at the bottom of the cooling tower. Light hydrocarbons like paraffin with low boiling points accumulate near the top of the top. This process is known as fractional distillation. The different hydrocarbons have different uses. For example, bitumen is used to surface roads while paraffin is mostly used as aviation fuel.

Evolution of atmospheric Oxygen

Atmospheric O2 accelerated the diversification of life by permitting aerobic respiration. Eukaryotic (nucleated) cells evolved by at least 1.0 Ga—a big step on the way to multicellular life. O2 buildup resulted in the formation of the ozone layer, which blocked deadly ultraviolet (UV) radiation. Prior to the ozone layer, exposed land was bathed in UV.

Evidence of free oxygen

Atmospheric oxygen (O2) skyrocketed between 2.4 to 2.2 Ga as a result of cyanobacteria (blue-green algae). Evidence of oxygen buildup is preserved in banded iron formations (BIFs), which are red because of oxidized iron (Fe). BIFs, which occurred worldwide during this time, are major iron ores today.

what causes decay

Atomic nuclei are held together by an attraction between the protons and neutrons (called the "strong nuclear force"), which has to be greater than the electrostatic repulsion between the positively-charged protons within the nucleus for the nucleus to remain stable. In general, the number of neutrons in an atomic nucleus must at least equal the number of protons because electrostatic repulsion prohibits denser packing of protons. If there are too many (or too few) neutrons, the nucleus has the potential to become unstable. Decay happens spontaneously at any time when the electrostatic repulsion is greater than the nuclear force that holds the nucleus together.

Mesozoic

By the end of the Triassic, the first true dinosaurs evolved. Dinosaurs differed from other reptiles by having their legs beneath their bodies (instead of to the side). Some bear evidence of warm-bloodedness. In the Jurassic, giant sauropods were present. Oddly enough, Tyrannosaurus rex was NOT a Jurassic dinosaur.

Uniformitarianism

Charles Lyell's idea that geologic processes have not changed throughout Earth's history.

super continents

Continental collision created Proterozoic supercontinents. Rodinia was a supercontinent that formed ~1 Ga coinciding with the Grenville orogeny in North America. Rodinia rifted apart ~700 Ma. The formation and breakup of several large super continents

properties of radioactive decay 1

Each parent isotope decays at a specific rate and changes of the pressure, temperature or chemistry in typical earth environments do not change that rate. Because radioactive decay takes place in the nucleus of the atom, it is controlled entirely by the micro-scale interaction between the strong nuclear force and electrostatic repulsion, and is not influenced by any external conditions, such as temperature or pressure or the occurrence of chemical reactions (the latter of which is mainly controlled by the electrons). Each clock ticks at the same rate no matter what.

complex cells forming

Eukayotes- multicellular life first appear, 2.1Ga

black shale

However, under certain conditions there may be very little oxygen on the sea floor. This may be because the ocean is deep and stagnant and oxygen has not been mixed down from the surface waters. No animal life can survive where the sea bed is completely lacking oxygen. Without animals to eat the dead plankton, the organic mush builds up on the sea bed. Where ocean sediment contains more than 5% organic mush it eventually forms a rock known as a Black Shale. The black colour comes from the dark organic matter that it contains. As we will see, Black Shale is what makes oil and gas.

where do hydrocarbons come from

In certain parts of the world's oceans, plankton occurs in enormous quantities, or blooms. Exactly where those plankton blooms occur is controlled by ocean currents. The richest sites are where cold, nutrient rich waters rise to the surface from the deepest parts of the ocean. The nutrients found in these 'upwelling zones' feed plankton and allow them to reproduce quickly

closure temperature

In some cases, heating a mineral to a sufficiently high temperature can "open the box", with the usual result being the loss of daughter products. If this happens, our clock will not begin recording time again until the box "closes" by falling to a sufficiently low temperature. We refer to the temperature roughly marking the transition between open and closed behavior as the "closure temperature".

Varves

Light and dark layers of sediments deposited in a yearly cycle

mesozoic shale

Most of the Source Rocks that gave rise to our present day oil and gas fields were formed in the middle of the Mesozoic Era about 150 million years ago. At that time conditions were just right to build up huge thicknesses of Black Shale. On the one hand, the oceans were unusually warm, promoting vast plankton blooms. On the other hand, oxygen was mostly absent on the ocean floors so most of the plankton that settled on the bottom accumulated. There were no animals around to eat it up. The map on the left hand side shows what the Earth looked like 150 million years ago. The red circles show where the world's main oil deposits were formed in warm, shallow, deoxygenated seas.

landscapes beneath sea

Oceans exist because of differences in lithosphere. Continental lithosphere "floats higher" on the mantle. Oceanic lithosphere "floats deeper" in the mantle. Ocean basins collect water because they are lower.

transport

Presenter notes: Once the oil and gas has been extracted from the ground, it must be safely transported from the well to the refinery where it will be processed. Oil is usually transported from the well to the refinery using pipelines. These may stretch over land or be laid over the sea bed. A spectacular example of an oil pipeline is the Trans-Alaskan pipeline which carries oil and gas for 1300 kilometres across Arctic permafrost. Another way that oil and gas are transported is by means of massive oil tankers. These gigantic vessels can carry up to half a million tonnes of oil.

forming streams

Sheet wash erodes the substrate and creates tiny rill channels that coalesce, deepen, and downcut, eventually concentrating flow in a single channel.

zircon crystals

Some durable minerals can be thought of as "boxes" which incorporate some amount of radioactive elements when they form, and hold the daughter products inside as they are generated. We can use the ratios of parents to daughters in these minerals to determine an age.

creatous tertiary boundary effect

Strong evidence indicates that the Cretaceous was closed by a catastrophic impact of a meteorite 13 km across. This impact created a huge crater, created a tsunami 2 km high and set forests ablaze. The impact blasted so much debris into the atmosphere (including sulfate aerosols from vaporized gypsum) that it blotted out the sun and shut down photosynthesis. Analysis of the clay revealed that it is highly enriched in iridium (Ir), an element rare on Earth and abundant in meteorites. Geologists began to find iridium enrichment in K-T boundary clay worldwide. Evidence for an impact includes a thin layer of plankton-free clay that separates plankton-rich chalk at the K-T boundary. This suggests that plankton were shut off for a short time. The clay contained other unusual material including pressure-shocked quartz and tiny glass spheres called microtektites, features found elsewhere associated with impacts.

Archean Eon

The Archean Eon, the time between 4.0 and 2.5 Ga, witnessed the birth of continents and of life on Earth. By ~3.85 Ga, Earth had cooled to form lithosphere, intense meteorite bombardment ceased, and parts of the rock record begin to survive. The volume of continental crust increased dramatically (by the end of the Archean, ~85% of modern continental area was present). This indicates that plate tectonics was in action.

Coriolis effect

The Coriolis effect occurs because the velocity of a point at the equator, in the direction of the Earth's spin, is greater than that of a point near the pole. Due to the Coriolis effect, currents deflect clockwise, relative to the wind in the northern hemisphere. Currents spiral by Coriolis deflection into large gyres.

snowball earth

The Ediacaran fauna arose in conjunction with two events: the assembly and breakup of Pannotia and a global cooling possibly resulting in a "snowball Earth." Life diversified rapidly after snowball conditions waned.

ordovician

The Ordovician saw the first vertebrates (jawless fish), crinoids, green algae, and primitive land plants. The end of the Ordovician witnessed a mass extinction. The seas roiled with diverse life (trilobites, brachiopods, crinoids, gastropods, cephalopods, corals, sponges, bryozoans, algae, etc.). The land, however, was barren.

Phanerozoic Eon

The Phanerozoic is the most recent 541 Ma of Earth history. It began with the first hard-shelled organisms, which greatly increased fossil preservation. Hard parts made a more complete archive of past life possible.

GTS

The composite geologic column is divided into time blocks that are the equivalent of Earth's calendar. This is the geologic time scale. The large time blocks are called eons. They represent hundreds to thousands of Ma. Eras are subdivisions of an eon (65 to hundreds of Ma). Periods are subdivisions of an era (2 to 70 Ma), and epochs are subdivisions of a period (0.011 to 22 Ma).

principle of fossil succession

The fossil range describes the first and last appearance of a species. Each fossil has a unique range. Sometimes the ranges of unique organisms overlap.

half life

The half-life is the time it takes for half of unstable nuclei to decay. The half-life is a unique characteristic of each isotope. As a parent disappears, the daughter "grows in" or increases. After one half-life, one-half of the original parent remains. After three half-lives, one-eighth of the original parent remains.

anthropocene

The land surface of the Earth has been changed radically during the Anthropocene. What was a grassland only a few centuries ago has become a grid of streets and buildings in Chicago.

properties of radioactive decay

The nuclei of some naturally occurring isotopes are unstable.

Eons

The primary defined divisions of time are eons, in sequence the Hadean, the Archean, the Proterozoic and the Phanerozoic. The first three of these can be referred to collectively as the Precambrian supereon. Eons are divided into eras, which are in turn divided into periods, epochs and ages.

baked contacts

The principle of baked contacts observes that an igneous intrusion cooks the invaded country rock. The baked rock must have been there first (it is older). A chill margin is formed within the igneous intrusion at the contact from rapid cooling.

cross cutting relations

The principle of cross-cutting relations holds that younger features truncate (cut across) older features. Faults, dikes, erosion, etc., must be younger than the material that is faulted, intruded, or eroded. (A volcano cannot intrude rocks that aren't there yet).

principle of inclusions

The principle of inclusions explains the occurrence of one rock fragment within another. Inclusions are always older than the enclosing material. Weathering rubble must have come from older rock. Fragments (xenoliths) within an igneous intrusion are older.

Lateral Continuity

The principle of lateral continuity observes that strata often form in laterally extensive horizontal sheets. Subsequent erosion dissects once-continuous layers.

original horizontality

The principle of original horizontality states that, because sediments settle out of a fluid by gravity, they tend to accumulate horizontally. Sediment accumulation is not favored on a slope. Hence, tilted sedimentary rocks must be deformed. Layers are originally placed flat. Exceptions are crossbedded sandstone and volcanic strata

Superposition

The principle of superposition states that in an undeformed sequence of layered rocks, each bed is older than the one above, and younger than the one below. Younger strata are on top; older strata are below.

passive & active

The sea floor exhibits highly varied bathymetry. Passive margins occur on both sides of the Atlantic. Active margins border the Caribbean and the western coast of South America. Continental shelf—shallow

Stream Discharge

The volume of water that passes through an imaginary cross section across a stream. Expressed at some volume per time e.g. meters3/second Increases downstream Controls amount of material a river can carry

angular unconformity

Tilted and/or folded sedimentary rocks, overlain by younger layers that are more flat-lying

formation of reducing atmosphere

Volcanic outgassing created a deadly atmosphere of N2, NH3, CH4, H2O, CO, CO2, and SO2. Meteorites bombarded the surface between 4.0 and 3.9 Ga. Liquid water condensed to form the oceans. First evidence of oceans from marine sediments ~3.85 Ga.

cambrian explosion

We find the ancestors of all major divisions of life present in the Cambrian, leading people to wonder what was so special about that time, to create such diversity seemingly so suddenly. We now know that part of the story starts back in the late Precambrian, with the Ediacaran fauna.

Earliest life

We know that life first appeared during the Archean, based on biomarkers and isotopes. The first chemical evidence of life is ~3.5 Ga, and life may have existed as early as 3.8 Ga. The oldest bacterial cell fossils are ~3.2 Ga. Stromatolites, layered mats of cyanobacteria (blue-green algae), appeared ~3.2 Ga. Cyanobacteria changed Earth's atmosphere forever by converting CO2 and H2O into hydrocarbon food and a catastrophically deadly waste product: free oxygen.

The source of oil: Plankton organic preservation in marine sediments

When plankton dies it slowly settles to the sea bed where it forms an organic mush. (most plankton is respired by bacteria)Usually there are lots of animals living on the sea floor that feed on this material. One important group is the polychaete worms. These are detritivores, which means they eat the dead and decay remains of other organisms and they turn it into CO2

Ekman Effect

Wind drags water Ekman spiral- looking down at currents - they appear to spiral Ekman transport - average flow of water throughout the spiral is ~90° to the right of the surface wind in the northern hemisphere

crude oil

a mixture of longer chain hydrocarbons (several carbon atoms) in soil and liquid phases. Can be separated into components with differing number of carbon atoms based on boiling point (kerosene, gas, tar etc)

Hadean Eon (4.6-3.8 bya)

began with the formation of Earth by planetesimal accretion. Earth was heated by impacts and radioactive decay and was hot enough to partially melt by ~4.5 Ga. The molten Earth underwent chemical differentiation as gravity pulled molten iron into the center. The ultramafic mantle remained as a thick outer shell. After differentiation, Earth was smashed by a Mars-sized protoplanet that blasted a part of Earth's mantle into space. The debris from the collision formed a ring around Earth that coalesced into the Moon. Thus, the Moon has the same composition as Earth's mantle.

alluvial fans

high energy (steep gradient, mountainous terraine) streams carrying coarse loads emerge from canyon to open plain

radioactivity clock

lDuring radioactive decay, the number of protons in the atom changes, and one element transforms into another. lParent isotopes decay into daughter isotopes. l lRadioactive Decay is sort of like popping popcorn. each radioactive parent decays to a specific daughter, and radioactive isotopes decay at a certain rate, once it decays it can not change back

hydrocarbon

large molecules made up of hydrogen atoms attached to a backbone of carbon

Late proterozoic

life became much more complex but still no bones, 640-540 ma, soft bodied animals

varying base levels

nBase-level changes cause stream readjustments. Raising base level results in an increase in deposition. Lowering base level accelerates erosion. Base level is the lowest point to which a stream can erode. Ultimate base level is sea level. A lake serves as a local (or temporary) base level.

headwater erosion

nHeadwater erosion occurs via intense scouring where sheet flow enters uppermost part of channel

thalweg

nThe deepest part of the channel (and usually the highest current velocity) is called the thalweg.

stream velocity

nThe rate of flow (not the amount of water) e.g., meters/second nControls how large material a stream can carry nDischarge and velocity not equivalent - can have high discharge with slower velocity in large rivers

Hypothermophiles - first life?

nrRNA Phylogeny indicates that the hyperthermophiles are the most ancient Hypothermophiles are clustered near the base of the bacterial and archaeal domains nSo the earliest life must have evolved under pretty extreme conditions like the Archean

Competence

nthe maximum particle size that a stream can transport. uDepends on stream velocity

Gas (natural gas or methane

short chain hydrocarbon with 1 carbon atom

geologic time scale (GTS)

system of chronological dating that relates geological strata (stratigraphy) to time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history. The table of geologic time spans, presented here, agree with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS).

base level

the downward limit to which a stream will erode its channel

Deep Time

the immense span of geologic time. Human history is miniscule when compared against deep geologic time.

capacity

the total quantity of sediment that a stream can carry. Depends on velocity and discharge

meanders

where rivers approach base level (flat), velocity decreases (but high order so high discharge and capacity) low gradient means that lateral migration dominates over downcutting Meanders evolve over time, becoming more sinuous (by cut bank erosion and point bar growth) before eventually being chopped off. The highest-velocity water erodes the outside of a bend, which is called the cut bank. The inside of the bend (the point bar) is the site of sediment deposition.

enhanced recovery

• Although oil and gas are less dense than water and naturally rise up a well to the surface, in reality only 40-50% of the total will do so. • To enhance recovery, a hole is drilled adjacent to the well and one of the following: gas, steam or chemical is pumped down. These help to solubilize the oil and push it out of the rock and up into the well.

hydrothermal vents

•Inhospitable environment of early earth (intense UV radiation, repeated bombardment by meteorites, warm temperatures may necessitate evolution in a subsurface hydrothermal environment • •Presence of essential enzymes and nutrients supports this hypothesis

Reservoirs and traps: accumulating oil

•Once produced and migrated from the source rock, hydrocarbons need to accumulate somewhere •Reservoir: a rock with sufficient porosity and permeability to allow for hydrocarbon accumulation •Trap: a structural or stratigraphic feature that allows hydrocarbons to accumulate in the subsurface.

oil migration

•Once produced at depth the byproducts (liquid oil and gas) will buoyantly migrate upwards •Primary migration: movement out of the source rock to a more porous rock •Secondary migration: movement through the carrier rock to a trap.

OPEC

•Organization of the Petroleum Exporting Countries (OPEC) is a group of 13 countries that produce 36% of the world's oil, or 32 million barrels of oil per day. • The biggest producer is Saudi Arabia, but Iran, United Arab Emirates, Kuwait and Venezuela are also major suppliers

Seismic Surveys

•Seismic surveys are used to locate likely rock structures underground in which oil and gas might be found • Shock waves are fired into the ground. These bounce off layers of rock and reveal any structural domes that might contain oil

Sedimentary strata form laterally continuous layers until they:

•abut against older rock •pinch out •are truncated by erosion •are cut by a fault