SIO 10: Midterm Study Guide

What evidence do we have for understanding Earth's composition and structure?

- asteroids → Earth composition

- lab experiments → properties of Earth material at depth

- seismic waves → density and phase (solid/liquid) of Earth material

- pull of gravity → Earth mass → density → relative amount of dense material (iron)

When H/He supplies get low, what are the different paths a star can take?

- several involve the explosion of the star in a "supernova"

What does a supernova constitute?

- supernova synthesize heavier elements

- most elements heavier than oxygen are made this way

SLIDE 7

chart of abundance of elements in the Milky Way

Where do the elements (different kind of atoms) come from?

** Big Bang = Hydrogen

** Stellar fusion (stars) = Helium, Carbon, Oxygen, Neon, Silicon, Sulphur, Iron

** Supernova = Lead, Uranium, Thorium

Describe the basic steps in the formation of the Solar System according to the nebular theory

1. A nebula forms from H/He left over from the Big Bang, and from heavier elements that were produced by fusion reactions in stars or during explosions of stars

2. Gravity pulls gas and dust to form an accretionary disk; eventually a glowing ball --the proto-Sun-- forms at the center of the disk

3. "Dust" (particles of refractory materials) concentrates in the inner rings, while "ice" (particles of volatile materials) concentrates in the outer rings; eventually, the dense ball of gas at the center of the disk becomes hot enough for fusion reactions to begin; when it ignites, it becomes the Sun

4. Dust and ice particles collide and stick together, forming planetesimals

5. Forming the planets from planetesimals: planetesimals grow by continuous collisions; gradually, an irregularly shaped proto-Earth develops; the interior heats up and gravity reshapes the planet into a sphere

6. Gravity reshapes the proto-Earth into a sphere; the interior of the Earth differentiates into a core and mantle

Which planets in the solar system are the "ice giants", "gas giants", and "terrestrial planets"?

- Ice = Uranus and Neptune

- Gas = Jupiter and Saturn

- Terrestrial = Mercury, Venus, Earth, and Mars

How do ice giants and gas giants differ in their location, size and internal composition from the four "terrestrial" planets?

- ice = Rocky, a lot of water ice, and molecular hydrogen

- gas = Molecular hydrogen, metallic hydrogen, rock, ice

- Mercury: atmosphere (none), temperature (180-430℃), surface water (none)

- Venus: atmosphere (50x thicker than Earth), temperature (470℃/ 864 F → melts lead), surface water (none)

- Earth: atmosphere (Earth-like), temperature (cool/warm), surface water (yes)

- Mars: atmosphere (thin), temperature (cold), surface water (ice)

Which terrestrial planets are considered to be in the "habitable zone" of the solar system?

Earth and Mars

What makes the habitable zone habitable?

- it is at the right temperature to host liquid water (not to hot to boil, not too cool to freeze)

-

Why did Earth differentiate over time into a rocky (silicate) mantle and a nickel-iron core?

- Earth is mostly comprised of just four elements: Oxygen (30%), Silicon (15%), Magnesium (13%), and Iron (35%)

- Iron is heavier stuff, so it sank into the core

What are the principal internal layers of Earth, and how do temperature and pressure change with depth?

1. crust (rocky, cool, solid)

2. mantle (rocky, hot, solid but able to flow)

3. outer core (iron, really hot, liquid)

4. inner core (iron, really hot, solid)

** In the outer core, the temperature (geotherm) is slightly higher than iron's melting point (solidus)... which is why the outer core is liquid.

What aspects of the core (e.g. composition, structure) are responsible for generating Earth's magnetic field?

- The source of Earth's magnetic field is the motion of liquid iron in the outer core

- magnetic field protects life on Earth

What is the "Big Bang"?

- the "Big Bang" (hypothesis for the earliest history of universe); formation of Hydrogen and Helium (the simplest elements)

^ gravity causes the collapse of H/He gas clouds into first stars; nuclear fusion in stars burns light elements to produce (a) energy and (b) heavier elements, up to Iron (Fe)

What are the layers made of?

- Crust: Oxygen, Silicon, Aluminum

- Mantle: Oxygen, Magnesium, Silicon

- Core: iron

What differentiates the oceanic crust from the continental crust?

- Continental = light and thick

- Oceanic = dense and thin

What differentiates the lithosphere from asthenosphere?

- Lithosphere = rigid layer; crust AND mantle

- Asthenosphere = weaker/soft layer; mantle only

**distinction based on physics rather than chemistry

^^ boundary is due to temperature differences within the mantle (rock begins to flow like a very thick liquid)

What is the Moho boundary?

- Moho boundary is due to compositional differences between crust and mantle (different elemental abundances)

What is the "transition zone"?

"transition zone" boundaries are due to rock phase change caused by increasing pressure and temperature within the mantle (same elements change into different combinations)

What is a mountain belt?

What is an abyssal plain?

a broad, relatively flat region of the ocean that lies at least 4.5 km below sea level

What is an ice sheet?

a vast glacier that covers the landscape

What are seamounts?

underwater mountains formed by volcanic activity

What is a trench?

a deep, elongate trough bordering a volcanic arc; defines the trace of a convergent plate boundary

What is a mid-ocean ridge?

a 2 km high submarine mountain belt that forms along a divergent oceanic plate boundary

What is a fracture zone?

a narrow band of vertical fractures in the ocean floor; lie roughly at roughly angles to a mid-ocean ridge, and the actively slipping part of a fracture zone is a transform fault

What is the continental shelf?

- a broad, shallowly submerged fringe of a continent; ocean-water depth over the continental shelf is generally less than 200 meters

- the widest continental shelves occur over. passive margins

What is a plain?

a large area of flat land

What was the continental drift hypothesis proposed by Alfred Wegener in 1912?

- The continents as we know them moved into their present locations very slowly over time, and that they had actually started out as a single huge landmass called "Pangaea" (Pangea)

- He called it "Kontinentalverschiebung" = "continental" "shift" (or drift)

What were the scientific observations which Wegener used as evidence for continental drift?

- Fit of the continents

- Locations of past glaciations

- Distribution of climatic belts

- Distribution of terrestrial fossils

- Matching geological units

Why were geologists initially skeptical of Wegener's new ideas?

** great hypothesis for explaining a diverse set of observations, but it lacked a plausible mechanism by which it could occur

- The scientific community needed more evidence to convince them to reconsider their assumptions about how the Earth worked

- This took decades to materialize, and was the result of new technology

Describe the hypothesis of seafloor spreading and how spreading is supposed to work.

* Harry Hess's theory for seafloor spreading:

- Mid-oceanic ridges are where hot magma rises and forms new crust, pushing the sides of the ridge apart; shallow ridge earthquakes are due to rising magma breaking the crust

- Young oceanic crust ages as it moves away from the ridges -- cooling, sinking (as it becomes more dense), and accumulating sediment

- At the deep-ocean trenches, oceanic crust is "subducted" or recycled back into the mantle, causing deep earthquakes

Why was Hess's theory of seafloor spreading adequate?

- Solves question of why we see ridges and trenches

- Explains increasing sediment thickness away from ridges

- Explains why seismicity is located at ridges and trenches

- Explains observations of high crustal heat flow at ridges

How can marine magnetic anomalies be used to calculate rates of seafloor spreading?

- Earth's magnetic field changes polarity regularly

- Ocean crust is magnetized with the polarity present when it formed

- We can map the resulting "marine magnetic anomalies" from ships

What happens to the dipole during normal polarity vs reversed polarity?

normal polarity = dipole points south

reversed polarity = dipole points north

What is a tectonic plate?

a portion of Earth's lithosphere (rigid crust + rigid part of mantle) that moves as a single unit relative to other plates

Where is global Seismicity (Earthquakes) concentrated and why?

- at plate boundaries

- there must be a lot of stress on the (brittle) lithosphere at plate boundaries.

What are the types of plate boundaries?

divergent, convergent, transform

What is a divergent boundary?

- the place where two plates move apart, or diverge

- mostly occur along mid-ocean ridges and land

- youngest crust is always at the ridge

- mid-ocean ridge width = 1.7 cm/yr

What is a convergent boundary?

- the place where two plates come together, or converge, the result of a collision

- trenches, volcanic arcs, subduction zones

What is a transform boundary?

- a place where two plates slip past each other, moving in opposite directions

-

What happens at divergent margins in the ocean?

- pillow basalts form

- ex) Juan de Fuca Ridge (offshore Pacific NW)

What happens at divergent margins on land?

- rifts

- ex) Afar rift, Ethiopia (East African Rift)

Where is there a convergent plate boundary on Earth?

- Japan (4 intersecting plates, 3 trenches)

** Pacific plate motion

- India-Asia Collision Zone

What is happening at convergent boundaries?

- on lithospheric plate is moving under another (creates an accretionary prism which is the sediments from oceanic plate)

- less dense material "sinks" while denser material "rises"

** sinking lithosphere may go to the core-mantle boundary

What is the San Andreas Fault?

- a transform boundary between the North American and Pacific plates

- it links spreading centers (divergent boundaries) north of San Francisco and south of the Salton Sea.

- The Big Bend (where CA meets Mexico) restricts motion on San Andreas Fault... perhaps encouraging new transform fault inland

What is mantle convection?

- the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat

- Convection in the mantle drives various contributors to plate motion:

^ (subduction pulling the plate with it)

^ (ridge spreading pushing the plate)

^ (mantle dragging the plate from below)

What is a hotspot and hotspot track?

- Hot Spot: region of concentrated volcanic activity; plume of hot material that rises through the mantle and can cause volcanoes

- Hot Spot Track: line of volcanos that show history of crust moving over hot spots

What is an example of a hotspot on Earth?

- Ages of the Hawaii islands show a progression from young to old

^ "Big Island" is oldest (as the plate moves, the hotspot moves and causes new volcanoes to form)

What do Continuous GPS (Global Positioning System) stations do and where are they stationed?

- track current crustal motion

- stationed in Greenland, Mount Soledad, and Nepal

SLIDE 52-54

tectonic plate motions of Western US and the world

What is a rock?

a naturally occurring solid that typically consists of one or more minerals arranged in an irregular pattern

What is a mineral?

a naturally occurring solid that has a crystalline structure (atoms all arranged nicely, like stacked oranges) and a uniform elemental composition

What is an element?

a species of atom with a fixed number of protons in the nucleus (Hydrogen is an element with 1 proton, Carbon is an element with 6 protons)

93% of the WHOLE EARTH is comprised of these 4 elements:

- Iron (33.3%)

- Oxygen (29.8%)

- Silicon (15.6%)

- Magnesium (13.9%)

95% of Earth's CRUST is comprised of these 5 elements:

- Oxygen (46%)

- Silicon (28%)

- Aluminum (11%)

- Iron (6%)

- Magnesium (4%)

What are the 3 basic rock classifications?

metamorphic, igneous, sedimentary

What is igneous rock?

rock made from the freezing (solidification) of melt (molten rock)

What are the typical locations of igneous rock formation?

mid-ocean ridges, hot spots, subduction zones

What igneous rock can we see being created in "real time"?

Pillow lava

What types of igneous rock realms are there?

EXtrusive and INtrusive

What is extrusive igneous rock?

- in the extrusive realm: ash flow, ash fall, ash cloud, lava flow, volcanic debris flow

- EX) Thick Mafic Lava Flow (flood basalts): Basalt Columns

What is intrusive igneous rock?

- magma cooling slowly below Earth's surface in a magma chamber

- EX) Broad Intrusions: Batholiths (Cooling, Crystallization, Erosion)

- EX) Narrow Intrusions: Dikes (cuts across layers) and Sills (pushes between layers)

Difference between A'a and Pahoehoe? (SLIDE 65)

Same lava composition, but different appearance due to flow speed (fast = A'a, slow = Pahoehoe)

What is a sedimentary rock?

rock formed at or near the surface of the Earth in one of several ways, typically at low temperatures.

What are the steps that solid ("fresh") rock undergoes in order to become sedimentary rock?

1. Starts as rock: a naturally occurring solid that consists of an aggregate of minerals

2. Weathering

- Weathered rock: rock that is weakened and/or broken down, but still in place

3. Erosion, mass wasting

- Sediments: loose fragments of rocks or minerals broken off of a host rock → also refers to fragments that are further broken down due to erosion/transport

4a. Either Transport to Lithification

- Depositional environment: palace and/or conditions where sediments collect

4b. Or just straight to lithification

- Lithification: compaction and cementation of sediments to form sedimentary rock

5. Sedimentary Rock

What is the difference between weathering and erosion?

- weathering: if a rock is changed or broken but stays where it is

- erosion: if the pieces of weathered rock are moved away

What is a depositional environment, and where are they typically found?

- Depositional Environment: place and/or conditions where sediments collect

- desert environments = with little water, transport of eroded rock stops at the base of the mountains and sediments build up as an alluvial fan

^ EX) Death Valley and Antelope Canyon

What is lithification?

compaction of sediments + cementation

What are sediments?

loose fragments of rocks or minerals broken off of bedrock, mineral crystals that precipitate directly out of water, and shells or shell fragments

sediment before and after lithification to sedimentary rock

- angular clasts (sediment) -> glacier/mountain -> breccia (sed rock)

- river gravel -> river -> conglomerate

- beach/dune sand -> desert/estuary -> sandstone

- mud -> estuary -> shale/mudstone

SLIDE 76

sedimentary rock formations

Other Sedimentary Rocks

- Corals (shallow marine) → limestone

- Plankton shells (deep marine) → chalk

- Plants (marsh/estuary) → coal

- Sodium chloride → Halite/Table Salt (evaporite)

What is metamorphic rock?

rock that forms when a pre-existing rock undergoes changes due to exposure to high pressures, high temperatures, high shear stresses and/or fluids deep within the Earth

Metamorphism...

... generally occurs at 200 degrees Celsius and hotter, and usually at pressures that are thousands of times atmospheric pressure ... which means it happens deep within Earth's crust

Pressure during metamorphism...

... causes compression in the direction of preferred orientation

SLIDE 82

metamorphism and heat over time

High pressure and heat during metamorphism causes what type of rock to form?

Limestone (protolith) -- (heat + pressure) --> Marble

Why do we use metamorphic rock (marble) for white buildings rather than its protolithic sedimentary rock (limestone)?

better durability

What is a shear?

- flattening of rock

- creates a diagonal/slanted formation

SLIDE 87

Classic metamorphic rock "look" due to shearing and flow under high temperatures/pressures.

rock cycle

the series of processes that change one type of rock into another type of rock

What is a volcano?

- a vent from which melt from inside the Earth spews out onto the planet's surface

- a mountain formed by the accumulation of extrusive volcanic rock

What is a magma chamber?

a space below ground filled with magma

What is a conduit vent?

- the pipe or vent at the heart of a volcano where material wells up from beneath the surface

- the pipe that carries this magma from the magma chamber, up through the crust and through the volcano itself until it reaches the surface

What is a crater?

- a circular depression at the top of a volcanic mound

- a depression formed by the impact of a meteorite

What is a caldera?

a large circular depression with steep walls and a fairly-flat floor, formed after an eruption as the center of the volcano collapses into the drained magma chamber below

What is magma?

Molten rock beneath the earth's surface

What is lava?

Magma that reaches Earth's surface

What comes out of an unplugged conduit?

gas, ash, rock, lava

what are the two eruptive styles?

flow (effusive) and blow(explosive)

what characterizes an effusive eruption?

- Less viscous magma

- Less gas & water

what characterizes an explosive eruption?

- More viscous magma

- More gas & water

What is the Hawaiian Fountain?

- Lava Fountains (small)

- lava

What is the Strombolian?

- Rock Fountains (small)

- rock

What is the Vulcanian?

- Lava/Rock Fountains (medium)

- lava and rock

What is the Plinean?

- Rock/Ash Explosion

- rock, ash, and gas

What types of lava flow are there?

basaltic: has a low viscosity and can flow long distances

andesitic: is too viscous to flow far and tends to break up as it flows

felsic: so viscous that is may pile up in a dome-shaped mass

What happens at a plugged conduit?

- Pressurized magma chamber, partially melted, containing dissolved gas

What are two eruption mechanisms?

- Eruption Mechanism #1: "Lava" etc. squeezed out of the top of the "volcano" by pressure from the "magma chamber" walls

^ Pressure Release: SLOW

^ Eruption Type: Effusive

- Eruption Mechanism #2: "Lava" etc. pushed out top of "volcano" by pressure from expanding by gas (and water vapor). This can be the stronger force by far!

^ Pressure Release: FAST

^ Eruption Type: Explosive