SCI 141 Earth Science Exam 1

earth science

the study of the earth, the materials it’s made of, it’s surface and interior processes, history, and it’s place in the solar system and universe

James Hutton

• father of modern geology

Uniformity

the earth as we know it today is the very long-term result of processes that are still taking place today (different rates in the past) → the present is the key to the past

Rules of Logic

1. Superposition

2. Original horizontality

3. Cross-cutting relationships

Superposition

in a sequence of layers, the oldest will be on the bottom 

Original horizontality 

most layered rocks are composed of sediment, and layers of sediment start out flat 

Cross-cutting relationships

a layer must exist before it can be cut through

Relative Dating

requires comparisons, so that we can put things in a sequence or order

Fossils

• remains or trace evidence of life preserved from the past 

• bones, shells, whole thing, turns to stone (no DNA), feces 

Correlation with fossils

time interval over which species existed

fanual succession and the geologic time scale

• fossils followed each other through the geological record in a predictable order 

• allowed them to compare the ages different areas based on the groups of fossils found there 

What killed the dinosaurs?

• impact hypothesis

• astroids, volcanos

• block sunlight → plants die 

Absolute dating with radioactive isotopes

• unstable radioactive parent isotopes transform (decay) into stable “daughter” isotopes by giving off energy and/or particles (radioactivity)

Half-life

how long it takes for half of the radioactive sample to turn into the daughter product

t = 1 half life (1/2 P0)t = 2 half lives (1/4 P)

age of the earth

earth has been dated using radiometric dating of meteorites to an age of 4.6 billion years 

Alfred Wegener

early observations:

• shape

• fossils

• rocks

• glaciers

• magnetic

Continental Drift

A hypothesis that the continents used to all be joined together into a single supercontinent called Pangaea, which broke apart, and the continents then moved over/through a passive ocean floor to their current locations (Alfred Wegener)

Later evidence: The Ocean Floor

• topography (bathymetry)

• magnetic evidence/age 

• seafloor spreading (Harry Hess)

Later evidence:

• evidence from earthquake and volcano locations 

• knowledge of the interior of the earth 

Layers of the earth

1. Crust

2. Mantle

3. Core

Crust of the earth

• oceanic: younger, thinner, heavier

• continental: older, thicker, lighter 

Mantle of the earth

• Lithosphere (rigid): crust + uppermost mantle

• Asthenosphere (plastic): portion of mantle below the lithosphere which allows plates to move on top of it 

Core of the earth

• outer core - liquid

• inner core - solid 

Principle of isostasy

weights balance across earth’s surface

Theory of Plate Tectonics

• the entire earth’s surface (both continents and ocean) is broken up into (mostly) rigid sections known as lithosphere plates

• these plates move on top of the ductile asthenosphere

• plates now move over time, and interact with each other along the boundaries where they touch

Tectonic Boundaries 

• continent divergent 

• ocean divergent

• continent transform

• ocean convergent 

• continent convergent

Divergent

• plates move apart, volcanic activity, earthquakes 

• ex: mid-atlantic ridge

Convergent

• plates move together; if one or more parts are oceanic, we get a trench/subduction zone 

  • volcanic activity, earthquakes (could be large)

• ex: west coast of South America

• if both parts are continental, we get a a collision (no more trench) → mountain building, big earthquakes

  • Ex: Himalayan mountains

Transform

• plates grind side by side → earthquakes (large)

  • San Andres Fault 

What drives tectonics?

heat deep within the earth and the force of gravity lead to mantle convection 

Characteristics of Mountain Ranges

• many (not all) are linear

• many (not all) are situated along the edges of current of former boundaries between plates 

• always being weathered and eroded, but will grow taller as long as forces building them up are greater than those breaking them down

• can spread under their own weight 

• deep crystal roots and undergo isostatic adjustment throughout their existence 

Mountains forming

• the process of mountain building is called “orgenesis” or “orogeny”

  • compressional forces

  • extensional forces

  • heat/vertical forces from below 

  • accumulation of volcanic material

  • differential weathering 

compressional forces

convergent

extensional forces

divergent or spreading/stretching (Basin range Nevada) 

Heat and uplift coming from below 

• Adirondacks 

• oldest formation exposed on the surface 

• oceanic ridges - divergent (volcano)

• above subduction zones (convergent with oceanic)

• above mantle hotspots (volcano) 

what is an earthquake?

• a sudden motion of the ground due to the release of energy stored in rock 

• can occur along new or pre-existing faults a

What is a fault?

• a crack in a rock where there has been displacement(movement) across the crack 

• most (but not all) faults where earthquakes occur are along plate boundaries 

Rock behavior

rock stresses can be: 

• compressional, extensional, or shear 

rock responses can be:

• elastic, brittle, plastic 

faults exhibit “stick-slip” behavior 

Seismic waves

• body waves

• P waves 

• S waves

• Surface waves 

• Rayleigh waves

body waves

through the entire earth

P waves “primary”

• arrive first at seismometer, travel the fastest; travel in solid and liquid; moves particles in forward/backward, push/pull, like sound 

• from the location of the shadow zones we can infer the depth to the outer core

S waves “shear/secondary”

• arrive 2nd, travel 2nd fastest, travel in solid only, cause motion in up/down way

• from the location of the shadow zones we can infer the depth of the outer core and that it is liquid

Surface waves

arrive last, do most damage, love waves - horizontal side/side shaking 

Rayleigh waves

rolling motion of the ground

Earthquake locations

• requires 3 circles, one for each location where you have information about the distance to the quake

• where all 3 circles overlap is where the earthquake happened

what can we learn from records or earthquakes?

• data about the earthquakes that generated those records (seismographs)

• information about other events that transmit energy through the earth (such as nuclear tests)

• structure of the interior of the Earth

can we predict earthquakes

no, we do not have the technology

what factors affect earthquake intensity?

• size, distance, and depth 

• type and quality of construction

• type of rock/soil in the area

• population size/density 

• time of day/year

• local economic prosperity

• amount of preparation

• secondary effects: landslide, tsunami, disease outbreaks 

how do we mitigate the effects of earthquakes?

• construction practices

• preparation

• education 

Tsunami Awareness 

can travel about 500 miles an hour, for thousands of miles across the ocean 

Weathering vs. Erosion

weathering - breaking down of material

erosion - movement; moving material from one place to another 

Rocks weather and erode at different rates 

Mechanical weathering 

changes only the size and shape of the pieces, not their composition 

• frost wedging

• pressure release

• plant growth

• temperature contrast

• abrasion

can happen at the same time as chemical

Chemical weathering

changes the composition of the sediment through interactions with the air, water, or other solutions

• oxidation

• carbonation

• hydration/hydrolysis

can happen at the same time as mechanical

Soil

• an important product of weathering is soil

• contains both weathered rock and organic material

agents of erosion

• gravity/mass movement

• wind

• running water

• glaciers

mass movement can occur for many different sizes and types of materials, and ranges from very slow to very fast speeds

Factors that destabilize slopes

• increased steepness

• increased water content

• decreased vegetation

• addition of weight

• triggering events

Wind

• transports small particles of miles

• particles also abrade, and pick up more

Running water

what controls how much erosion running water can do? Speed

the velocity of a stream depends on: 

• the shape and roughness of the channel

• the steepness of the slope (gradient)

• fullness of the streambed

a stream’s discharge is found by multiplying its velocity by the cross-sectional area of the stream

Evolution of stream system

young: relatively straight path, downcutting into a V shape valley, steeper gradient

mature: meanders (curves) develop, erosion is side to side, flood plain develops, flow is slower, flatter gradient

old: very wide flood plain, oxbow lakes develop 

evidence of stream deposition 

• streams sort sediment by size/weight because when the water slows down, it deposits the largest/heaviest particles first

• the smallest particles are deposited in the slowest moving water

Alluvial fans

• water slows down after coming out of mountains when it meets flat valley floor 

• these and deltas are depositional features 

• as sediment is moved, it is also being weathered

  • the farther a rock travels from its source, the more likely it is to become smaller, rounder, and more polished 

glaciers 

• long-lasting masses of ice formed on land from the accumulation of snow 

• they can be continental “ice sheets” or alpine “valley” glaciers 

continental glaciers

form over large are and spread under own weight

alpine (valley) glaciers

form in mountains and flow downhill

Moraine

pile of glacial sediment along front or sides of a glacier 

drumlins

pile of glacial sediment formed into long, parallel, thin hills 

Where is the water on the earth?

• more than 97% of earth’s water is in the oceans

• the next largest reservoir is in glacial ice

The hydrologie cycle

the force of gravity and energy from the sun propel water from place to place around the earth 

the water cycle

1. evaporation

2. condensation: droplets of water forms clouds 

3. precipitation: rain, snow, hail

Plants → evapotranspiration 

groundwater

gravity causes water flow from higher elevations to lower elevations, and from areas at higher pressures to those at lower pressures 

Flooding

• runoff occurs when precipitation exceeds infiltrations

• what factors lead to increased flooding?

  • excess rain fall, concrete, pavement (reduces infiltration) 

water as a resource

do most people in the US treat water as a precious resource?

no