Exam 1 Flashcards
What is geology?
- the study of physical structure and composition of all solid planetary bodies
- the physical processes that act on and within these planets
- geologic history
Why natural science core classes?
- jobs
- science minded voting public
- science is objectively amazing
How many Americans believe the sun revolves around the earth?
26%
How many Americans believe the earth is less than 10,000 years old?
26%
How many Americans reject evolution?
38%
What is scientific literacy?
- science involves ideas, theories, and facts
- behind the facts is a rigorous, repeatable process
- any unbiased/objective method to solve a problem involves the scientific method
Steps of the scientific process
make observations
think of interesting questions
formulate hypotheses
develop testable predictions
(refine, alter, expand, reject hypotheses)
gather data to test predictions
develop general theories
Example of theory = Newton’s theory of gravity:
determines the force of gravity between two objects
developed in 1680s, still used
accurately predicted planet locations in solar system
not perf, failed to account for gravitational force of more than two objects (sun pulls on mercury but so do other planets)
Albert Einstein’s theory relatively took over in 1916
What do geologists do?
- petroleum / coal industry exploration
- water management (hydrogeologist)
- floods (hydrologists / geomorphologists)
- economic geology
- environmental geology (cleaning, testing, etc.)
- earthquakes (seismologists)
- volcanoes (volcanologists)
- paleontologists (dino, fossils)
- ## planetary geologists
When was the origin of our solar system?
4.6 years ago
How did our solar system begin?
from hot gasses and dust, the remnants of a dead star (Nebula - step A)
What is step A in the origin of our solar system?
protoplanetary nebula stage (a collection of gasses)
What occurs in the protoplanetary nebula stage? (A)
the gasses come from a star that recently died, when a star reaches the end stages it can explode or lose its shell of gasses for space, the gasses are weakly attracted to each other by gravity
the composition (elements) of the gas is dependent on the elements that were in the original star (hydrogen&helium most abundant but also could be oxygen, carbon, iron, etc. - these elements are made inside of the star by nuclear fusion
a new star and planets will coalesce from these gasses
What happens to a dying star?
gasses are shed from the exterior, it can no longer hold them, the gasses that escape into space can coalesce again under gravity to form a new star and planetary system
Supernova explosion:
much more massive stars (giants/supergiants) die catastrophically and explode, the nebula of hot gasses can coalesce under gravity to form a new star and planetary system
What is step B of the origin of our solar system?
a protoplanetary disc: gasses collapse under gravity and begin to rotate around a center of mass (our protosun) in a disc
What occurs in the protoplanetary disc stage (B)?
the gasses will begin to attract to each other due to gravity, the sneer of mass of the nebula, in the region of the original star/explosion, has the highest concentration of gas, coalescing the gas here may birth a new star (a protosun) if enough mass can accumulate to initiate nuclear fusion
the protosun is the hot center of the disc, the gravitational attraction of the protosun controls/holds remaining gasses and a disc of gas develops, they are still very hot (hundreds of degrees)
What is step C in the origin of our solar system?
accretionary disc, gas cools and metals begin to solidify (Fe, Al, Mg, K, Ca, Si) larger objects attract to each other by gravitational attraction
What occurs in the accretionary disc stage (C)?
as the gasses in the protoplanetary disc cool, the gas particles turn to liquid droplets, and then eventually to solid particles, metal elements turn solid first and some gaseous elements never turn solid (like hydrogen) the solid particles in the disc begin as just small grains of dust, as they whip around the sun, they attract each other (by gravity) and collide
Accretion
the process where solid particles attract each other due to gravity, collide, and make larger objects (this process is responsible for making larger mass objects in our solar system like the sun and other planets)
Accretion in depth:
the “seed” of a planet begins as nothing more than a slightly larger piece of dust that attracts (by gravity) even smaller pieces of dust to it, as that seed becomes larger, it attracts more and more fragments of material due to gravity (more massive objects have more gravitational force) this makes the seed larger and larger, eventually a larger planetoid emerges and begins to clear out everything in its orbit (pluto is an example of a small planetary body - a dwarf planet that even today, has not cleared out its orbit completely this is why it is no longer considered a planet)
Definition of a planet:
- is in a stable elliptical orbit around the sun (can’t find colliding w sun for example)
- has sufficient mass reach hydrostatic equilibrium (round) [outward pressure=gravitational pressure]
- has cleared the neighborhood of other objects in the same orbit around the sun (where pluto fails) [can’t share orbit w another]
Hydrostatic equilibrium
state of balance by which the internal pressure of body exactly balances its gravitational pressure [self gravity=internal pressure] (gravity pulls the planet inward, exerting inward directed pressure, internal heat is trying to escape outwards {space}, exerting outward pressure, thus creating a balance –> h.e.
Asteroids
(few cm to 10 km in size) rocky bodies (sometimes icy) that are not large enough to be considered planets
may not have coalesced into large planets (accumulated enough debris via accretion) or are remnants of failed planets (planets that exploded due to large collisions during accretion phase
(ex. our moon formed from a large collision between earth and a mars sized object (thea) early on in the accretion disc
Protoplanets
(100s of km in size)
small planetary bodies that did not form into a full planet, they are almost round (ex. vesta is the largest still in our solar system, in the asteroid belt, never managed to coalesce because there wasn’t enough debris in its neighborhood)
Dwarf planets
(about 1000 km in size)
not full grown planets, relatively small, spherical bodies that look almost just as full planets, these never cleared out of their orbit the debris (other large bodies in their orbital path)
(ex. pluto in the outer solar system, ceres is the largest in the asteroid belt - between mars and jupiter)
Size of full planets
1000s to 10000s km in size
Why did the earth have a magma ocean phase?
around 4.5 billion years ago, heat collisions of objects (the formation of the moon) and radioactive elements within earth during and immediately after accretion phase leaves the early earth partially to mostly molten
What are the sources of heat from earth’s magma?
collision with other objects: even while this is still technically in accretion phase, large objects that are in unstable orbits collide with the earth (and all planets) some could completely melt
radioactive elements: this generates heat energy, radioactive elements decay over time, early earth had a lot that are now gone, the heat generated from those early elements kept the interior hot, today its a little cooler
Moon formation hypothesis:
Giant Impact Hypothesis: our moon formed from the debris ejected from earth due to impact of a mars sized body (thea) the moon is 4.56 billion years old - some of the ejected material recoalesced in orbit around earth as our moon
Heavy bombardment
the moon has large impact craters (now filled with old lava) they 100s of 1000s of km in size in diameter and represent heavy bombardment phase of our solar system that continues even after the formation of moon (ending ~3.9 billion years ago)
Why are earth’s interior parts separated?
elements in our molten planet begin the separate based on their relative density, dense elements sink in the magma ocean, less dense floats
differentiation
Differentiation
process of density settling of elements in the hot earth that leads to formation of core, mantle, and crust (each layer has a different composition- chemistry)
What are the most common risk forming elements on earth?
Fe - iron
O - oxygen
Si - silicon
Al - aluminum
Na - sodium
Ca - calcium
K - potassium
Mg - Magnesium
What are the two most abundant elements in our crust?
Silicon (Si) and Oxygen (O)
Is there more iron (along with nickel) towards the crust or the core?
core
How do we know how the earth is separated?
rocks are brought up from our mantle
upper mantle rocks may get incorporated into magma (liquid rock)
Differentiation:
density settling (sink towards core, lighter in density floats up)
crust, mantle, and core is compositional zonation
Plate tectonics:
how plates move and interact w each other
when plates collide, the lower crust and sometimes the upper mantle are uplifted to the surface
brings deep materials to the surface
controversial until 1960s
Xenolith
a piece of rock that is foreign to the rock surrounding it
ex. piece black basalt volcanic rock from crust surrounding green chunk from our upper mantle
Xenolith
a piece of rock that is foreign to the rock surrounding it
ex. piece of black basalt volcanic rock from crust surrounding green chunk from our upper mantle
Two ways to classify core, mantle, and crust:
- composition
- phase of matter
Lithosphere
solid outer shell of Earth, contains the crust and part of the upper mantle, ridged, broken up into plates, brittle, directly above asthenosphere, biggest plate on planet, movement of this is what causes earthquakes
Asthenosphere
a more plastic-like sphere of the Earth, mostly solid, but is partially molten in parts, is ductile (a solid that can bend and flow) we call a solid that expresses that kind of ductile behavior a plastic solid (not actually a plastic like you think of plastic) this is a portion of the uppermost mantle of Earth
Mesosphere
the solid portion of the mantle (the rest of the mantle) this material is still hot enough that it can flow (a bit) and some ways does behave like a plastic, but its still completely solid and does not flow as easily as the asthenosphere
Outer core
the only entirely liquid interior sphere of the earth, the outer core is Fe and Ni in composition, but it is entirely molten
Inner core
also made of Fe and Ni, but it is under too much pressure to turn liquid, it is plenty hot enough to be liquid, but the confining pressure of the entire planet prevents the atoms from phase changing to liquid
Is there magma (liquid rock) beneath us?
not until you get to the core, around 3000 km down, magma/lava comes from crust/upper mantle and requires specific circumstances to stay, the mantle is almost all solid but behaves like plastic
How do we know the phases of matter inside the Earth?
earthquakes
Summary of earth’s internal structure
crust, mantle, and core is a compositional classification scheme (based on differences in elemental composition)
the lithosphere, asthenosphere, etc. is a classification scheme based on the phase of matter (solid, liquid, etc.).
How/when did plate tectonics become an accepted theory?
Continental Drift:
German meteorologist Alfred Wegener:
The Origins of Oceans and Continents published in 1915.
Pangaea supercontinent = “Fit” of the continents.
Developed hypothesis of continental drift.
Paleoclimatic Evidence (for Pangea)
~250 Myr old Glacial deposits (evidence of thick sheets of ice) near the equator today.
~250 Myr old tropical swamp deposits (coal) in present day eastern US.
~250 Myr old tropical coral reefs in present day midwest/southern US.
Subtropical deserts across North America and Europe (~250 Myr).
Fossil Evidence (for Pangea)
Fossils - lithified remains of tracks, traces, or body parts of organisms.
Similar land fossils of similar age (300 to 250 Myr) that span 5 continents that are now separated.
Southern part of Pangaea super-continent in picture below called Gondwanaland/Laurasia (South America, Africa, India, Antarctica, Australia).
These animals could not have possibly crossed the Atlantic Ocean. The best explanation is that the Atlantic Ocean didn’t exist when these animals were alive. Instead, South America and Africa must have been together.
Matching geology (for Pangea)
Geologic structures & mountain belts.
Rock types & ages.
(ex. Appalachians vs Atlas Mountains, Scottish Highlands
Ocean Floor Mapping: Post WW2 (for Pangea evidence)
In the 1950s, ocean bathymetry was measured (seafloor elevation) sound waves
Discovered…
An elevated ridge near center of every ocean basin.
Also found deep ocean trenches adjacent to large mountain ranges that stick up out of the water (Bathymetric profile of the Atlantic Ocean showing a Mid-Ocean Ridge, Bathymetric profile of the east Pacific Ocean showing an oceanic trench)
Magnetic rocks
- Fe-rich, silicate rocks found on the ocean floor (basalt)
- Contain magnetic minerals (magnetite)
- These rocks were formed by volcanism (lava)
- Magnetites aligned with Earth’s magnetic dipole (think of a bar magnet with a north and south magnetic pole)
- detected by magnetometers on ships
(ex. magnetite, basalt)
Magnetite/magnetization
- (Fe3O4) cools and crystallizes from magma/lava
- When magnetite cools to its Curie temperature (~570° C) it aligns with Earth’s magnetic dipole (north aligns to north, south to south)
Curie temperature:
the temperature below which magnetism sets in (with Fe-bearing magnetic minerals)
What do magnets have to do with plate tectonics?
When the magnetites formed in lava, they lined up with Earth’s magnetic field
Magnetic Anomalies on Seafloor
Magnetometers towed behind ships…they discovered =
- Magnetism in the rocks oscillates from north polarity (+) to south (-) as you move away from a Mid-Ocean Ridge.
- Linear belts (“stripes”) of + and - magnetization that parallel the Mid-Ocean Ridge.
Magnetism & Plate Tectonics
our magnetic field flips repeatedly but that the seafloor was/is spreading from the center of the ridge
Magnetic Field Reversals
Time average of reversals is ~450,000 years but it is highly variable
illustrates the switch of Earth’s polarity, normal (or positive) polarity is when Earth’s magnetic pole is pointing north, reverse polarity (or negative) is when the north magnetic pole points south
What movements occurred in the breakup of Pangea?
- spreading ridge offset by transform faults
- subduction zone
- motion of plate
Modern Evidence that Plates Move:
- earthquakes and volcanoes occur along specific boundaries – these correspond to the plate boundaries
- age of rocks on seafloor: Warm tones = young rocks/Cool tones = oldest rocks (The seafloor rocks also have “age stripes”. The youngest rocks are being erupted as lava from the crack at the Mid Ocean Ridge. As the plates spread out, the young rocks get pushed away from the central crack)
How can we measure plate motion?
Precision Global Positioning Systems (GPS) can be used to measure plate motion today - Average = 2 cm/yr
set up on top of crust, detects subtle movements
What formed due to plate tectonics?
ocean basins and continents
Why is there crust that rests above sea level and crust that rests below sea level? (large basins vs continents)
Isostasy & plate tectonics
Isostasy
a state of balance (equilibrium) in how the lithosphere is supported by the squishy/plastic upper mantle (asthenosphere)
easily demonstrated by floating anything on a fluid or plastic substance, iceberg is 10% above water and 90% below, lithosphere is iceberg and asthenosphere is water
Crust/Lithosphere Types
plates are made up of both oceanic crust/lithosphere and continental crust/lithosphere (sometimes both) + have different thicknesses and are made of different rocks (have different density) – this is similar to the wood analogy
Earth’s Crust:
Continental Crust – thick and less dense
Oceanic Crust – thin and more dense
Why is oceanic crust thinner than continental?
plate tectonics, it’s made where the plates spread across from each other, crust will thin where it spreads apart → the opposite is where the plates collide, crust will thicken, compresses and squishes together
What do oceanic crust plates do?
diverge - spread apart
the crust thins where plates spread apart – making ocean basins
What do continental crust plates do?
converge - collide
the crust thickens where plates collide – making continents
Why is oceanic crust denser?
- made of heavier things
- Granite (very common) it contains silicon and oxygen which is silicate, granite has aluminum in it (important metal in the rock) - Basalt, dominant metal is iron - Both of these are cooled magma, our crust is made from magma *these share silicates but their metals are different
The heavier things are here also due to plate tectonics!
What makes the crust/lithosphere?
cooled magma/lava by volcanism
magmas/lavas have a different elemental composition because they come from different parts of the Earth (crust vs. mantle)
Examples of new crust being made by volcanism:
- Iceland = oceanic crust
- Mt. St. Helens (Washington state) = continental crust
Why is the ocean crust made of Fe-rich silicates and continental Al-rich silicates?
- New crust is made by the cooling of magma/lava (volcanism).
- Note that magma is made at both divergent and convergent plate boundaries (more on this later).
- But, notice that the magma comes from a deeper mantle source where plates spread apart (divergence). More Fe in these lava rocks.
Which crust is more dense?
oceanic crust (resting lower in asthenosphere due to basins), continental is less (rests higher than asthenosphere, land we live on)
Lithosphere/Crust Type Classification:
Oceanic – Oceanic
Continental – Oceanic
Continental – Continental
Relative Motion Classifications:
Convergent
Divergent
Transform
Plate boundary combinations for divergent
Continent – Continent Divergent
Ocean – Ocean Divergent
Plate boundary combinations for convergent
Continent – Ocean Convergent
Ocean – Ocean Convergent
Continent – Continent Convergent
Plate boundary combinations for transform
Ocean – Ocean Transform
Continent – Continent Transform
Continent - continent divergent margin
Divergence in a continent generates a rift valley (thinning of crust)
The rift is bounded on either side by faults, where quakes occur
Center of the crust collapses along the faults as plates move apart
(ex. East African rift valley (in cross section), forming because the African continent is splitting apart, the valley in the middle (now filled with lakes and some volcanoes) is an expression of this divergence)
Which boundary are volcanoes commonly associated with?
divergent
Why is there volcanism at a divergent boundary?
- Remember: The mantle is normally solid (if not plastic) all the way through!
- The mantle is plenty hot enough to melt rock, so why isn’t it completely molten!
- The mantle is under intense pressure from overlying rock…too much pressure for the molecules to move.
- Release of pressure at divergent plate boundaries causes the upper mantle to partially melt (decompression melting).
Decompression melting
you can melt a very hot object by simply reducing the pressure on that object, you don’t have to raise its temperature
Ocean - ocean divergent
new ocean
As continental rifting progresses, a new ocean basin forms
Modern rifting in continental crust leading to new ocean
(ex. Red Sea - a location where the contents have split apart enough that sea water has begun to fill in the rift valley, This is the birth of a new ocean. Not simply because sea water is filling in a rift valley, but because as divergence continues and the crust thins, lava will emerge from the upper mantle and new, Fe-rich oceanic crust (basalt) will be born)
Ocean - ocean divergent margin
As rifting continues, the mantle melts can eventually reach the surface.
This produces thin, Fe-rich oceanic crust (basalt)!
The resultant rift valley/basin starts to fill with water to form an early sea and then an ocean.
Ocean crust is born
(ex. Mid-Atlantic Ridge)
Continent – Ocean Convergent
If new crust is created (divergence), old crust must be destroyed (convergence)
(a thin oceanic plate collides with a thick continental plate - The result of this kind of collision is a process known as subduction)
Ocean - Continent Convergent Plate Boundary
Ocean crust is recycled back into the mantle at *subduction zones
Subduction
process by which lithosphere/crust is destroyed or recycled back into the mantle
