Geology: Physical I Module 5 and 6

Uniformatarianism

- Observe how sediments are deposited in the modern

- Use observations to interpret sedimentary rocks deposited from the past.

Superposition

In undisturbed settings, oldest sedimentary rocks are deposited first at the bottom of the sequence.

Original horizontality

Sedimentary beds are originally deposited horizontally

Lateral Continuity

Sedimentary beds are originally deposited and extend laterally in all directions.

Inclusion

If a rock includes fragments of other rocks, the rock must be younger than the fragments.

Cross-Cutting

Faults, igneous rocks, or unconformities that cut across sedimentary beds are younger than the beds they cut.

Relative Age Dating

The science of determining the sequence in which events occur without absolute numerical ages.

Numerical age dating

Time(numerical) being assigned if possible .

Deposition (Time refrence)

Preserves info about change through time

Erosion of Sediments (Time reference)

Removes info from the geologic record.

Unconformity

- An erosion surface representing a gap in time between the formation of two sections of rock.

- Gap may represent 1000's, millions, or billions of years.

- Look for contrasts in orientation or type of rocks between adjacent rock units.

Three types of unconformity

- Angular unconformity

- disconformity

- nonconformity

Disconformity

Sediments above and below in the same position, but different sediment.

Angular unconformity

- mountains form

- rocks tilted up, exposed, erosion occurs and eventually mountains erode completely.

- difference in orientation below and above.

Nonconformity

- igneous/metamorphic rock with sediment on top.

- forms deep below surface, later uplifted to shallow depths. Weathering a erosion expose rocks.

Correlation

matches rock units to determine the relative ages of rocks between regions or continents.

Fossils

remains of living organisms preserved in rocks.

- used to correlate sedimentary rocks

- used to study evolutions and ecology

Body Fossils

Fossil remains of part or all of a dead organism.

- Cast or mold

- Shells/hard parts

- Bones

- Soft tissue

Trace Fossils

Remains of a living organisms behavior

- Footprints

- Tracks

- Root traces

- Burrows

As you move from the base of a section of rock, to the top, there were changes in and appearance of new _____________. The ___________ closer to the base represent different chunks of time, and show extinct species.

fossils

Index fossil

Species that lived a short time span so gives narrow age range

Biozones

Different types of overlap of fossils

What intervals of earth's history are rocks grouped into

3 Eons --> Eras --> Periods

What are the three big eons?

- Phanerozoic

- Proterozoic

- Archean

Life is bacteria in Archean and proterozoic

What do we call the Archean and Proterozoic and why?

It is commonly called precambrian when grouped together.

- This is because in both of these, there was mostly just bacteria that formed.

Name all Eras in order of oldest to most present:

- Precambrian

- Paleozoic

- Mesozoic

-Cenozoic

Events in Paleozoic

1. First common organisms with hard skeletons

2. First land plants

3. Age of fishes

4. Insects and early reptiles on land

Events in Mesozoic

5. Early dinosaurs and Age of reptiles

6. First birds

7. First grasses and flowering plants

Events in cenozoic

8. Large mammals abundant

Early Paleozoic events

Abundant marine organisms with hard shells like corals, crinoids, trilobites

Middle Paleozoic events

Age of fishes, large coral reefs, primitive land plants like ferns, and first insects

Late paleozoic events

Evergreen trees, amphibians and early reptiles on land, Pangaea

Mesozoic events

Age of Dinosaurs, first birds, first grasses and flowering plants, large marine reptiles, early mammals

Early Cenozoic events

Age of Mammals, first large mammals (elephants, whales), horses, bears common

Late Cenozoic events

Ice age in northern hemisphere, mammoths, first humans, modern organisms

Eras in Phanerozoic

Paleozoic, Mesozoic, Cenozoic

Big five extinction periods:

1. End Ordovician (57%)

2. Late Devonian (50%)

3. End Permian (83%)

4.End Triassic (48%)

5. End Cretaceous (50%)

Mass Extinctions : What is one cause?

- Giant rock hit planet

- "Geologically" sudden global extinction event.

- Strong correlation with rapid climate change (warming or cooling).

What was the basis of dividing the phanerozoic eon into eras?

because of two major extinction events

Arrange the list in the correct chronological order with the oldest at the bottom and the youngest at the top.

Early dinosaurs and Age of reptiles

Insects and early reptiles on land

Age of Fishes

First land plants

First common organisms with hard skeletons

Large mammals abundant

First grasses and flowering plants

First birds

Large mammals abundant

First grasses and flowering plants

First birds

Early dinosaurs and Age of reptiles

Insects and early reptiles on land

Age of Fishes

First land plants

First common organisms with hard skeletons

Match these statements to their corresponding stratigraphic principle.

Folding or uplifting of sedimentary beds must have occurred after the beds were deposited

Broken bits of rock found in another rock must be older than the rock they are inside

Faults, unconformities, and igneous rocks must be younger than the rocks they break through

The sequence of sedimentary rocks on either side of a river valley are likely the same

The oldest sedimentary rocks should be at the bottom

- original horizontality

- inclusion

- cross-cutting relationships

- lateral continuity

- superposition

Absolute (numerical) age dating

How geologists figure out the ages of rocks, and hence the age of Earth.

- age of earth is around 4.55 billion years(4,550 million years)

Numerical Time

How geologists figure out the age of rocks, and age of earth.

Half-Life

time for half the parent isotope to be converted to daughter isotopes.

When rock formed what percentage of parent and daughter isotopes?

100% parent, 0% daughter

As time passes, amount of parent isotope ___________ , daughter ___________.

decreases; increases

If you have 50% parent isotope and 50% daughter, what is the parent daughter ratio?

1:1

The radioactive isotope, X, decays to the stable isotope Y. The half-life for this process is 400 million years. Scientists analyze an igneous rock and find that it has 7-times as much Y as X. Approximately how old is the rock?

1200 million years

1:7 ratio(3 half-lives) so divide 400 by 2, 3 times.

If you have 25% parent isotope and 75% daughter, what is the parent daughter ratio?

1:3

If you have 12.5% parent isotope and 87.5% daughter, what is the parent daughter ratio?

1:7

The half-life of radioactive parent isotope is 400 million years. Scientists testing a rock sample discover that the sample contains three times as many daughter isotopes as parent isotopes. What is the age of the rock?

800 million years

Radioactive decay

- An element is originally formed (cooling of magma- igneous)

- Elements recombine to form new minerals under changing physical conditions (metamorphism)

- Decay has already begun for elements in minerals that form sedimentary rocks.

What are the three principles that are used for sedimentary rocks arranged in relative order?

Original horizontality, superposition, cross-cutting.

What is used to determine ages of metamorphic and igneous rocks?

Radioactive dating

"Understanding geologic processes active in the modern world is crucial to interpreting Earth's past."

What is the name of this concept?

a.Cross- cutting relationships

b.Superposition

c.Uniformitarianism

d.Index fossils

e.Original horizontality

c. Uniformitarianism

Put the following three units of time in order from shortest to longest.

a.

period, era, eon

b.

period, eon, era

c.

era, period, eon

d.

eon, era, period

e.

eon, period, era

a. period, era, eon

Which of the following is interpreted to be the same age as Earth?

a.

Moon

b.

Meteorites

c.

Venus

d.

The Sun

e.

The Universe

b,c,d

The early atmosphere of the Earth had much lower __________ concentrations than today and much higher ____________________ concentrations than today.

oxygen; carbon dioxide

During which Eon did the first multicellular organisms evolve?

Proterozoic

Identify which of the following statements are true.

a.

The divisions between eras in the Phanerozoic are marked by major extinction events

b.

The majority of species that have lived on this planet have gone extinct

c.

Oxygen had become relatively common in Earth's atmosphere during the time of Snowball Earth conditions.

d.

The first evidence of life on Earth is recorded in rocks approximately 3.8 billion years old

e.

The Moon represents a stray asteroid that was captured by Earth's gravity soon after the planet formed.

a,b,c,d

Which processes result in the decrease in the atomic number of an isotope following radioactive decay?

Electron capture

Alpha decay

If radioactive decay began with 600,000 parent isotopes, how many parent isotopes would be left after 3 half lives?

75,000

Approximately what age was determined for the oldest rocks that have been found on Earth?

4 billion years

Isotope X has a half-life of 10 days. If you began an experiment with a 400-gram sample of the isotope, how much isotope X would be left after 30 days?

50 grams

The half life of the isotope Uranium-238 is 4.5 billion years. The oldest rocks on Earth would contain approximately 52-55% of their original store of this isotope.

True

If you find an igneous rock which has 450 radioactive parent isotopes and 3,150 daughter isotopes, how many half-lifes of this isotope have passed since this rock first formed? Type the number in the space provided.

3

Radioactive isotope α decays into daughter isotope Ω with a half-life of 10 years. After 50 years, what should the ratio of parent to daughter isotope be?

1:31

Isotope G is radioactive and decays into daughter isotope H with a half-life of 100 years. You have a rock sample where the ratio of parent to daughter isotope is 1:3. How old is the sample?

200 years

Winds blow because air is pushed from areas of _________ air pressure towards areas of _________ air pressure.

high; low

Warm air rising off the surface of the planet results in areas of _____ air pressure and ____________ weather conditions.

low; cloudy/rainy

Air that is descending to the surface from the upper atmosphere results in areas of ___________ air pressure and _________ weather conditions.

high; dry

How many flow cells are present in the Northern hemisphere?

3

How many flow cells are present in the Southern hemisphere?

3

Due to the curvature of the Earth, sunlight strikes the poles at an oblique angle throughout most of the year. What happens to air at the poles?

It falls

The equator receives __________ direct solar energy throughout the year than the rest of the planet.

more

A "westerly" wind flows ___________

from the west

he "Trade Winds" form because air at the equator is ___________ , which creates a semi-persistent band of __________ air pressure.

rising; low

Air from higher latitudes moves towards the equator to fill that space, but its movement is deflected by ________________

the Earth rotation

Sediments that are directly deposited by a melting glacier are __________ sorted with ________ grains. This sediment is called ________.

poorly; angular; till

The term albedo refers to the proportion of sunlight that reflects off of a surface. The current albedo of the earth is about .3 (meaning roughly 30% of the light from the sun reflects off of the Earth's surface). What should happen to Earth's albedo during an ice age?

The average albedo of Earth's surface would increase

The last 800,000 years of Earth's history has been dominated by shifts between glacial periods (ice ages) and interglacial periods. The figure above shows the changes in average temperature of the planet over the last 450,000 years as interpreted from our ice core record. According to this figure, our last 450,000 years can be divided into ______________________________ and ____________________________.

long cold glacials; short warm interglacials

Match the following impacts to the Earth's energy budget with the Milankovitch cycle that would cause this change in the energy budget.

1. Affects the distance the Earth is away from the sun

2.Affects the seasonal distribution of solar energy

3. Affects the timing of seasonal changes as the Earth rotates around the sun

1. Eccentricity

2. Axis tilt/Obliquity

3. Precession

What changes would you expect to occur if the tilt of our axis were to decrease?

Colder summers, Warmer winters, Increase in the volume of glacial ice on Earth's surface.

What are things that makes Earth unique to sustain life?

- Distance from sun

- Type of star

- Good sized planet

- Magnetic field

- Breathable air

- Life Warming gases

- Liquid water

Average temp of the surface of the Earth?

15 C (59 F)

What do we call the position/zone of Earth from the Sun?

Habitable zone

Earth's size produces sufficient _____________ to hold a _________ atmosphere of ____________ in place.

gravity ;thick ;gases

What is earths magnetic field caused by?

Convection process in outer core due to plate tectonics

What does earths magnetic atmosphere deflect?

Solar winds

* Earth prevents solar winds from stripping away our atmosphere.

What are the 2 most common gases in Earth's atmosphere?

Oxygen and nitrogen

Composition of air

Nitrogen: 0.78%

Oxygen: 21%

Carbon Dioxide: 0.04%

Argon: 0.93%

Methane: 0.00018%

Greenhouse gases

Carbon Dioxide: 0.04%

Argon: 0.93%

Methane: 0.00018%

What is the purpose of greenhouse gases?

maintain temperatures on earth high enough to support life

When CO2 levels are low, temp is __________. And vice versa.

low

How does CO2 warm the planet?

It absorbs earth's outgoing radiation and re-emits it back toward the surface.

Climate

weather trends over extended period

Weather

day to day conditions ;short term state of atmosphere

What does the amount of solar energy (insolation) reaching Earth's surface depend on?

the angle the Sun's rays strike Earth

Rising air is at what degrees?

60 degrees N/S

Falling air is at what degrees?

30 degrees N/S