Geology Review 12&13

Rhythmic layering

Layering that develops due to seasonal changes in sedimentary accumulations and glacier ice

Fission Track

Line formed by the ejection of an atomic particle during the decay of a radioactive isotope which damages the crystal

Describe two different methods of correlating rock units. How was correlation used to develop the geologic column? What is a stratigraphic formation?

Over broad areas fossil correlation is used, because sources of sediments and depositional environments may change from one location to another. Sediment may look very different, but can still be the same age. Lithologic correlation is where geologists correlate formations between nearby regions based on similarities in rock type. Correlating helped form geologic column by allowing geologists to compare rocks at millions of different places, which helped create the composite stratigraphic column Stratigraphic formation is a sequence of bed of a specific rock type that can be traced over a broad region

What does the process of radioactive decay entail?

Parent isotopes are changing into daughter isotopes.

Uniformitarianism

Physical processes we observe today also operated in the past at roughly the same rate

Salt is a mineral, but the plastic making up an inexpensive pen is not. Why not?

Plastic is man-made, while salt is found in nature

Geologic map

Portrays the spatial distribution of rock units at the Earth's surface

What is the prime characteristic that geologists use separate minerals into classes?

Principal anion or anion group

Isotopic Dating

Process of determining the numerical age of racks

How do Geologists obtain an isotopic date? What are some of the pitfalls in obtaining a reliable one?

Radioactive elements decay at a constant rate over time, and they can be measured by comparing the parent isotope with the daughter isotope. Pitfalls:

Carbon-14

Radioactive isotope of carbon that naturally in the atmosphere when cosmic rays bombard atmospheric nitrogen 14

Craton

Region of old and relatively stable continental crust

Correlation

Relationship between the strata at on locality and strata of another

Compare numerical and and relative age

Relative age is the age of a formation with respect to another formation. Numerical age is actual age of a feature in years.

Fossil

Remnants of once living organisms in sediment

On what basis do mineralogists organize silicate minerals into distinct groups?

The arrangement of the silica tetrahedron

Nonconformity

The boundary between an old sequence of sediment, and new sequence.

What may have caused the flooding during the Cretaceous PEriod

The cretaceous mid-ocean ridges occupied more volume than today due to shallow depth

Phanerozoic Eon

The last 542 Million years of earth's history. Appearance of hard shelled organisms

Why can't we date sedimentary rocks directly

The mineral component of sedimentary rocks are generally older than the rock itself (Inclusion_

How did the atmosphere and tectonic conditions change during the Proterozoic Eon?

The plates went from small and fast moving to large and slow moving. Oxygen become abundant

Geologic time

The span of time since Earth's formation

How are growth rings and ice cores useful in determining the ages of geologic events?

They can help determine how long an organism survived. Ice cores can keep track of what the climate was like, and the temperatures.

Describe the principles that allow us to determine relative ages of geologic events

Uniformitarianism- Physical processes we observe today also happened in the past at roughly the same rate. Original horizontality- Sediments on Earth settle out of a fluid in a gravitational field Superposition- Each layer must be younger than the one below it in a sequence of sedimentary rocks

How does the principle of fossil succession allow us to determine the relative age of strata

We can say one bed is older than another bed based on the fossils found within them

How do you distinguish cleavage surfaces from crystal faces on a mineral?

Cleavage planes tend to be smooth and shiny, while crystal faces are not.

List and define the principal physical properties used to identify a mineral

Color, streak, luster, density, hardness, special properties, breakage(fracture/cleavage),

Geologic Column

Composite stratigraphic column of Earth's history

Pleistocene ice age

Continental glaciers expanded and retreated across northern continents around 20 times during the Quaternary Period

Radioactive decay

Converts isotopes into a different element

Describe the condition of the crust, atmosphere, and oceans during the Hadean Eon

Crust was liquid, atmosphere was composed of dangerous chemicals such as methane, carbon, sulfur

Daughter isotope

Decay product

Isotope

Different versions of an element

Stromatolite

Distinctive mounds of sediment produced by mats of cyanobacteria

Era

Division of Eon

Epoch

Division of Period

Period

Division of era

Why are there no whole rocks on Earth that yield isotopic dates older than 4 Ga?

During Hadean Eon, no rocks were present, Earth's surface was liquid

Hadean Eon

Earth bombarded by planetesimals, very hot, dangerous gases in the amosphere.

Proterozoic Eon

Earth went from small fast moving plates and low oxygen to large, slow moving continents, and huge amounts of oxygen

What are the major organisms that appeared during the Paleozoic?

Eel like organisms, shelled organisms that became more complex, vertebrae animals, plantkton

Why do some minerals occur as euhedral crystals, whereas others occur as anhedral grains?

Euheral crystals have well formed crystal faces(Geodes), Anhedral grains don't have well formed crystal faces

Superplume

Extremely active mantle plumes

Angular unconformity

Formed where rocks were tilted by folding or faulting before being exposed to Earth's surface

Describe srveral ways that mineral crystals can form

Freezing of a liquid, precipitation from a solution, solid-state diffusion(movement of atoms through a solid), interfaces between the physical and biological Earth System though biomineralization, and precipitation directly from gas (volcanic vents, geysers)

Why is glass not a mineral?

Glass is not crystalline in structure

Differentiation

Gravity pulling iron toward the center of the earth

Precambrian

Hadean, Archean, and Proterozoic

Half-life

How long it takes for half of a group of parent isotopes to decay

What major climatic and biologic events happened during the Pleistocene?

Ice age

Cross-cutting relations

If one geologic feature cuts across another, the feature that has been cut is older

Superposition

In a sequence of sedimentary rock layers, each layer must be younger than the one below

Parent isotope

Isotope that undergoes decay

How did the Cambrian explosion of life change the nature of the living world?

It was a huge diversification of life. Earth went from inhabited to habited really quicly by many differetnt organisms

Phanerozoic

Last 542 Million years of Earths history

Proterozoic Eon

2 Ga- 542 Ma

Great oxygenation event

2.4 Ga, photosynthetic organisms thrived, and there was a buildup of oxygen, because the plants had enough oxygen. The oxygen built up in the atmosphere. Created Banded Iron Formations (BIFs)

End Triassic

200 Ma

End Permian

251 Ma

Archean Eon

3.85-2.5 Ga

Late Devonian

375 Ma

What is the age of the oldest rocks on Earth? What is the age of the oldest rocks known? Why is there a difference?

4.03 Ga, 4.57 Ga. They come off of different planets, so they can e older than Earth rocks

End Ordovician

444 Ma

End Cretaceous

66 Ma

Eon

A major division of geologic time

What is a mineral, as geologists understand the term?

A mineral is a naturally occurring solid, formed by geologic processes, that has a crystalline structure and a definable chemical composition

Stratigraphic formation

A sequence of beds of a specific rock type that can be traced over a fairly broad region

Unconformity

A surface that represents a period of non-deposition and possibly erosion

What continents formed as a result of the breakup of Pangaea

Africa, South America, Antarctica, and Australia

Numerical age

Age of a feature in years

Relative age

Age of one feature with respect to another in a sequence

How does an unconformity develop? Describe the differences among the three kids of unconformities.

Angular unconformity- Formed when rocks were tilted by folding or faulting before being exposed at the Earth's surface. Disconformity- Beds of rock parallel to each other, but have a measureable age difference between them Nonconformities- Happens when sedimentary strata \are deposited on top of crystalline (metamorphic or igneous) rock

Disconformity

Beds of the rock sequence above and below the unconformity are parallel to one another, but there is a measurable age difference between the two sequences. The disconformity surface represents a period of nondeposition and/or erosion

Hadean Eon

Birth of Earth-3.85 Ga

Contact

Boundary surface between two formations

Shield

Broad, low lying area in which basement older than about 1 Ga is exposed in abundant surface outcrops

How can you determine the hardness of a mineral? What is the Mohs hardness scale?

By comparing it to other minerals. By using the Mohs hardness scale, you compare the hardness of a mineral to common items.

What evidence do we have that Earth nearly frozeover twice during the proterozoic eon?

By finding glacial sediments in places worldwide in the stratigraphic sequence

Stratigraphic column

Summarization about the sequence of sedimentary strata at a location

What life forms appeared during the Mesozoic?

Swimming reptiles, coral, flying reptiles, dinosaurs

Closure temperature

Temperature where isotopes are no longer free to move

geologic time scale

Numerical ages of periods and eras in the geologic column

Cratonic platform

Occupies the Midwest and high plains of the U.S

Fossil succession

Once a fossil species disappears at a horizon in a sequence of strata it never reappears higher in the sequence. Extinction is forever.

What could have caused the K-T Extinctions?

The 14 km meteorite

Index Fossils

Species' that existed for a short interval of the geologic column, and are found in a specific time interval

Stratigraphic sequence

Strata deposited on the continentduring periods when continents were submerged

Magnetostratigraphy

Study of comparing the pattern of the reversals in a sequence of strata with the pattern of reversals in a reference column. Helps determine age of a sequence

Cambrian Explosion

Major diversification of life

Pangaea

Result of a succession of continental collisions

Growth rings

Rings that form due to seasonal changes. Happens in trees, travertine deposits, and shelly organisms

What major tectonic provinces formed in the western United States during the Cenozoic?

Rocky Mountains

Original Horizontalty

Sediments on Earth settle out of a fluid in a gravitational field

Geochronology

Study of numerical ages

Archean Eon

Substantial amounts of crustal rocks formed

Cambrian Explosion

Sudden diversification of life