BIO/ENV 220: Intro to Earth Science Exam 3 Flashcards

The outermost portion of Earth’s crust is referred to as the _____ zone. Rocks in this portion of the Earth respond to stress by cracking and/or moving in a process known as ______ _________.

brittle; brittle deformation

Deeper in Earth’s crust, in a region referred to as the _____ zone, rocks respond to stress by undergoing changes in size, shape, and mineralogy known as _________.

ductile; metamorphism

Where do deeper earthquakes happen? What process drives this?

Convergent boundaries; Subduction

Sketch 3 Types of Faults (label them, use arrows to indicate direction of slip, and indicate the stress associated with each fault type)

3 Types of Faults and Stress Associated with Each Type

Normal → Tension at divergent boundaries

Reverse → Compression at convergent boundaries

Strike-slip → Shearing at transform boundaries

Describe OR sketch the concept of stick-slip behavior as it applies to earthquakes

Stick-slip behavior describes fault motion that results in an earthquake. Friction along the fault causes them to “stick” and build up stress, causing deformation of the rock. Eventually enough stress builds up to overcome the friction resulting in fault movement (slip)

What is the primary factor used to assess a region’s earthquake risk?

History of earthquake severity in an area

3 Main Types of Seismic Waves and a Note About Each

P-waves → Travel through interior; fastest; arrive 1st; horizontal vibration (spring)

S-waves → Travel through Earth’s interior; arrive 2nd; vertical vibration (rope)

Surface waves → Travel through Earth’s surface; arrive last

Difference between earthquake epicenter and focus

Focus → Focal point of split, considering depth

Epicenter → Location of earthquake on 2D map

What does the gap between P- and S- waves in a seismogram determine?

Distance between seismic station and epicenter of the earthquake

How is magnitude reflected in seismograph recording?

Amplitude

What 2 aspects of an earthquake determine its magnitude?

• Amount of slip along a fault

• Length of fault

Reasons why earthquakes are essentially impossible to predict (5)

1. No reliable precursor

2. No reliable way to measure stress/how much stress a fault can handle

3. No way to observe directly

4. Earthquake magnitudes varies along faults

5. Faults do not have clearly definable periodic behavior

Difference Between Magnitude and Intensity

Magnitude → standard measure of energy released (1-10)

Intensity → measure of effects on people and buildings (I-XII)

Why might two earthquakes with similar magnitudes have different intensities? (6)

• Weak v. Strong Sediment and Bedrock

• Water content of soil/sediment

• Landslides, tsunamis (secondary effects)

• Depth of earthquake (LARGE FACTOR)

• Citizen awareness and preparedness

• Quality of building construction

Largest Factor Differentiating Magnitude and Intensity

Earthquake Depth

What kind of faults most commonly produce tsunamis?

Reverse (compression)

What factors make tsunamis so destructive?

• Volume and Depth

• Speed and Strength

• Water Recession and Flooding

In a stack of rock layers, those at the bottom of the stack are ____ than those at the top of the stack. This is explained by the rule of stratigraphy known as ______.

older; superposition

If you observe a series of rock layers that are ______, this usually means tectonic activity has taken place in this area. This is explained by the rule of stratigraphy known as ________.

tilted; original horizontality

If you observe a “vein” of igneous rock running up through a stack of sedimentary rock layers, you can deduce that the igneous rock is ____ the sedimentary rocks. This is explained by the rule of __________

younger; cross-cutting relationships

An unconformity is a(n) _______ that represents a _______ between two rock layers

erosion surface; gap of time

3 Types of Unconformities

Angular → Flat layer deposited on tilted layers

Disconformity → Flat layer deposited on flat layer

Nonconformity → Flat layer deposited on non-sedimentary rock (i.e. granite, basalt, gneiss, schist, slate)

Estimated Age of the Earth and What it is Based on

4.54 billion; radiometric dating of meteorites

__________ isotopes decay to __________ isotopes. Decay occurs when an isotopes loses or gains ______ and/or _________, which changes the _________ or ___________ numbers.

Parent (unstable) ; daughter (stable) ; protons; neutrons; atomic; mass

The timing of radioactive decay is quantified using the concept of a ______

half-life

Half-Life Table

1: 50% P: 50% D

2: 25% P: 75% D

3: 12.5% P: 87.5% D

4: 6.25% P: 93.75% D

5: 3.125% P: 96.875% D

Formula for calculating age of rock

Age of Rock = # of half-lives passed x the length of one half-life

Why isn’t radiometric dating very useful for sedimentary rocks?

They are composed of older, weathered rock fragments cemented together

Mixed age components, no way to “reset” the clock

Basis for Earth’s Geologic Time Scale

Fossils

Major divisions of geologic time + relative lengths

Precambrian → 4.54 bya - 541 mya

Paleozoic → 541 mya - 250 mya

Mesozoic → 250 mya - 66 mya

Cenozoic → 66 mya - now

Supercontinents

3.5 mya partial melting formed continents

1.0 bya to 65 bya snowball earth, supercontinents

Chemical comp of atmosphere

Originally nitrogen and carbon dioxide, early photosynthetic bacteria increased concentration of O2 cause great oxygenation event wiping out many organisms. Single cell bacteria thrived

BIF

Great oxygenation event and oxidization of oxygen in oceans

Cambrian explosion

Beginning of Paleozoic 541 Mya signifies beginning of complex life

Precambrian, Paleozoic, Mesozoic, Cenozoic

Precambrian - Single celled bacteria GOE

Paleozoic - Cambrian explosion much complex life; extinctions

Mesozoic - age of dinosaurs, more reptiles on land, fish, marine organisms

Cenozoic - age of mammals, larger reptiles, angiosperms, grasss