GES 1101

Geo (Earth) ology (Study of)

• Uniformitarianism - processes that we see today are the same as in the past

  • The present is the key to the past

  • The past is the key to the future

• We can’t make future predictions without knowledge of geology and Earth’s history

Human History and the Origins of the Solar System

• “Earthrise”

  • Williams Anders, 12/2/1968

  • Taken 7 months before the moon landing

• Early astronomers started recognizing patterns in the night sky

  • Stars stay relatively fixed in relation to other stars

  • Planets move faster relative to stars

The Western World had two schools of thought

• Geocentric - Earth is the center, everything revolves around us

  • Ptolemy (100-170 CE), Egyptian mathematician

• Heliocentric - …

From there:

• Johannes Kepler determined the orbit of the earth around the sun is not a circular path but an elliptical one

Issac Newton explained:

• gravity is the attractive force one mass exerts on another, the magnitude is determined by the size of the objects and the distance between them

• This explains the movements that celestial bodies follow

County of the Day: Mecklenburg

• Epidote: ¾ mile east of exit 21 on 1-85 found in granite outcrops on the banks of Irvin Creek

• Epidote [Ca2(Fe,Al)3(SiO4)3(OH)]

  • Green to yellow to brown mineral that is often found filling vesicles in rocks such as basalt

  • Forms during hydrothermal alteration

Doppler Effect

• Change in frequency of a wave in relation to an observer who is moving relative to the source of the wave

Red Shift

• Galaxies with Red Shift must be moving away from the Earth at high velocity

1964: Discovery of Cosmic Background Radiation

Big Bang

• 13.8 Ga

• 13,800,000,000 years ago

Singularity

• Everything in the universe was packed in a single point

End of Inflationary Epoch

• The universe has cooled enough that hydrogen atoms formed

Temps cooled below 1 billion C

• Diameter of universe = 53 million km across

Big Bang Nucleosynthesis

• 10 sec - 20 min past Big Bang

• Elements: 

  • Helium 2

  • Lithium 3

  • Beryllium 4

  • Boron 5

• Next, elemental atoms began to combine (bond) to form molecules - molecular hydrogen (H2)

Covalent bond (sharing an electron) -> Universe continued to cool & expand - molecules slowed and accumulated into patchy clouds -> Nebulae

Nebulae

• Cloud of gas & dust in space visible in the night sky as an indistinct bright patch

• Gravity causes molecules to stick together

  • Specks of ice (not H2O ice)

• Now we have a swirly cloud of H & He ice + a few other molecules

  • This cloud’s gravity is increasing as mass is added

    • Nebulae become denser as the matter in them compress inward

• The denser the nebula becomes the more matter it attracts

• Nebula changes from a cloud to a disk

• More matter is added as the disk

• Eventually - gravity collapses the inner portion of then nebula into a ball

  • Temperature increases

    • Gas particles squeeze together

    • Center ball becomes hot enough to glow

• Protostar grows

  • Core is extremely dense

  • Temperature = 10,000,000 C

• Hydrogen nuclei create more He

  • Via fusion

  • This reaction creates energy (electro magnetic radiation)

• Proto star becomes a furnace

  • 1st rxn like this made the first true star (800 million years post Big Bang)

(True) Star

• Luminous spheroid of plasma that is held together by gravity

• This process continues to create the first generation of stars

  • 100x the mass of our sun

Larger = Hotter = Faster the star runs out of fuel & dies

Lifespan = few to few 10s of millions of years

1st Gen Star EXPLODES

Supernova

• Stars create increasingly heavier elements over their lifetimes

  • Emitted from stars via steller wind

• Most larger atoms are created when a star explodes

  • A functioning star cannot produce elements with an atomic number over 26

Our Sun currently

• 70% H

• 28% He

• 1.5% C, N, O, Ne, Si, Mg, S

  • Sequence Star

Death of a Star (Sequence Star):

1. Core runs out of hydrogen to convert into helium

   1. Energy produced by fusion creates pressure

      1. Pressure keeps the star from collapsing

2. Star continues to expand sub-giant giant star

3. Star makes Carbon (6) from He (2)

4. Star becomes unstable

5. Outer layers of star start blowing away

   1. Creates and expanding cloud of dust and gas

6. Star becomes a planetary nebula

7. Only the core is left

   1. Earth sized cinder

   2. Cools over several billion years

High Mass Star

• Core runs out of hydrogen to convert into helium

  • Oxygen 8

  • Neon 10

  • Magnesium 12

• Next step is fusing iron into a heavier element

  • Requires more energy than it produces

  • Instead of releasing it like the other reactions

• Iron core collapses and then rebounds

  • Creates a shock wave

• Supernova!

  • Neutron Star OR Black Hole!

But how do planets form?

Nebular Theory or Condensation Theory

Q: Why doesn’t the stuff in the disk fall into the center?

A: It’s moving fast enough to stay in orbit.

• Protoplanetary Disk in our solar system contained all 92 elements

Volatile Materials

• Substances that easily vaporize

  • Hydrogen

  • Helium

  • Methane (CH4)

  • Ammonia (NH3)

  • Water (H2O)

  • Carbon Dioxide (CO2)

Refractory Materials

• Only melt @ high temperatures

• Starts as fairly homogenous

• Sun begins to burn hotter

  • evaporates volatiles

Things that Orbit the Sun

1. Inner Planets

2. Other Planets

   1. far from the sun

3. Outer Bodies

   1. Comets

      1. Dust + Ice clumps

         1. “dirty, stinky snowball”

         2. Hale-Bopp Comet

            1. tail from outgassing

   2. Asteroids

      1. clumps of rock/metal material that never formed a planet

         1. leftovers from formation of solar system

         2. Vesta

         3. Most found between Mars & Jupiter

         4. mass of all asteroids in the solar system is less than the mass of our moon

4. Dwarf Planets

What defines a planet?

• International Astronomical Union

  1. Must orbit the sun

     • Not another object

  2. Must have gravity to become round

  3. Must have its own orbit

Things to consider (arguments from planetary scientists)

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County of the Day: Catawba

• Beryl:

• Soapstone:

• Graphite:

• Corundum:

• According to the county government: At the turn of the century, gold mining was a successful industry in Catawba County. Catawba County was a part of one of the largest gold producing areas in the entire country. North Carolina maintained its leadership in gold production until 1848 when it was eclipsed in importance by the great rush to California

Formation of Earth

1. Start with the protoplanetary disk

2. Clear the orbit

3. Chunks in the orbit collide, forming planetesimals

4. Planetesimals continue to collide and grow bigger through amalgamation

5. Irregularly shaped proto-Earth forms

6. Interior of Proto-Earth heats up

• Causes the interior to become soft

• 300-500 km diameter area

7. Gravity reshapes proto-Earth into a homogeneous sphere

8. The now spherical Earth continues to rotate and revolve around the sun

9. The interior of the earth differentiates into layers

10.  Another protoplanet collides with Earth

    1. Mars sized

    2. 4.5 billion years ago

    3. Collision blasts earth material into orbit around the sun

11. Moon forms from the orbiting debris

    1. Same process as planet formation in protoplanetary disk

    2. The moon clears the debris orbit

    3. Gravity reshapes the moon from a lump to spherical

Artemis III

1. First manned moon mission since 1972

2. Set to launch no earlier than mid-2027

3. Landing and collecting samples at the lunar south pole

Radioactive Decay Law

• To actually get the age of the earth we have to measure both Earth’s rocks and meteorites from the asteroid belt and in our nearby orbit plus Mars and the Moon to best constrain the age of the earth

• We don’t just measure 238U and 206Pb

  • There are many sets of half-lives to check and re-check the results

Early Earth

• 4.54 Ga

• Extremely hot

• Volcanoes erupting constantly

  • Volcanic gases formed the early atmosphere

• Tons of impacts from asteroids and protoplanets up until ~3.85 Ga

• Melting and remelting of the surface due to impacts

  • Impact energy turns into heat

• At high heat, heavy and light elements separate

• Forms the Core, mantle, crust, hydrosphere, and atmosphere

  • Water? From comets? Chemical reactions in minerals? Volcanoes?

• Water present by 3.85 billion years ago

  • Comets may have provided additional gases

Atmospheric Composition

• Earth cooled enough for water to condense

  • Rain

  • Oceans accumulated water

• CO2 from the atmosphere dissolved into the oceans

  • Precipitated into solids

  • Some settled out of the oceans

  • Trapped in the crust in rocks

• Oceans were full of dissolved iron (Fe)

Oxygen

• O2 only entered the atmosphere after organisms that photosynthesize evolved

  • O2 in the atmosphere by 1.8 Ga

  • Significant O2 by about 600 Ma

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County of the Day: McDowell

• Diamond: Dysartsville area in SE McDowell County. Placer mined pre-Civil War until a few years after the war ended

  • Historic reports of three (3) diamonds found

• Zircon:

• Corundum:

• Graphite

• Quartz

• Kyanite

• Beryl

• Garnet

Extra Credit Opportunity

Earth’s Magnetic Field

• Magnetosphere - region of space surrounding Earth that serves as a shield against solar wind

Earth’s magnetic field is generated by the convection of the outer core

Earth’s Structure

• Earth is made up of 92 naturally occurring elements but only 13 are common

  • C

  • N

  • Fe

  • Ni

  • Si

  • O

  • Mg

  • S

  • Al

  • H

  • Na

  • Ca

  • K

Structure of the Earth is based on chemistry and physics

• Driving principles: Pressure, temperature, and gravity

Composition of Earth’s Layers

How do we know the inner structure of the Earth?

• Earthquakes act like ultrasounds of the earth

• Earthquakes produce P-waves and S-waves

• P-waves - Primary waves, compression waves

  • P-waves move fast - first to arrive at seismic stations

S-Waves

• Secondary waves or shear waves

  • Think wiggling a string

  • S-waves move slower than P-waves

    • Arrive second at seismic stations

• Both P and S waves move through solids

  • Only P-waves move through liquids

  • Both can distort when they pass through materials of different densities.

    • Reflection and refraction

• Two other types of waves from earthquakes - surface waves

  • Love Waves - horizontal shearing

  • Rayleigh Waves - rolling waves

Mohorovicic Discontinuity (“Moho”)

• ~35 km below continents

• ~7 km below ocean crust

• Boundary between crust and mantle

• Defined by the change in velocity of seismic waves speeding up

  • There must be a change in properties of rocks here

Alfred Wegener

• German Climatologist and Geographer

• 1880 - 1930

• From a map view, it looks like the continents fit together like a jigsaw puzzle

Wegener began to investigate:

1. Analyzed rocks from both sides of the Atlantic Ocean

   1. Similarities between rock type, geologic structures, and fossils

   2. Hypothesis: all continents were once joined in a single landmass and had since drifted apart.

   3. Named the supercontinent “Urkcontinent” (Primal Continent) or “Pangaea” (All Lands)

Continental Drift!

Evidence for Continental Drift

1. Fit of the Continents

   1. Modern coastlines looks like they could fit together

   2. Very few gaps and overlaps

2. Locations of Past Glaciers

   1. Glacier - a river or sheet of ice that slowly flows across the land surface and lasts all year

      1. Not the same as icebergs

      2. Glaciers carry sediment

         1. Small chunks of rocks and minerals not attached to the subsurface geology. Includes clay, sand, silt, pebbles, and boulders

      3. The movement of ice carrying sediment leaves evidence

         1. Striations

         2. Glacial polish

         3. U-shaped valleys

         4. Hanging Valley Waterfalls

   2. By looking at evidence of past glaciers, geologists can figure out when past ice ages occurred

   3. Paleozoic Era Ice Age = 280-260 Ma

   4. Reconstructing the overall orientations of evidence + using the jigsaw method puts these areas together in the past

   5. Southern Pangaea around Earth’s South Pole

3. Climate Belts

   1. Rock records can tell you about the climate and physical geography of the area at the time of rock formation

   2. Coal = past swamp or jungle

   3. Limestone and Coral = Shallow, tropical ocean

   4. Sandstone with large dune structures = Deserts

4. Fossil Distribution

   1. If we find fossils from the same species on two continents that are now very far apart, it’s possible those land masses were once connected

   2. Darwin’s Theory of Evolution tells us that isolated species will evolve differently

   3. It’s not possible to have two species evolve identically across the ocean

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County of the Day: Rockingham

5. Matching Geologic Units

   1. Wegener found the same distinct pre-Cambrian (very old! At least 540 Ma) rocks in Eastern South America and Western Africa

   2. The Appalachian Mountains extend into Greenland, Europe, and Africa!

   3. Coast lines match!

   4. Inland rock units match!

The problem: How did the continents move?

• Did they float like rafts?

• Did they plow through the ocean flow?

• Did the centrifugal force of the Earth spinning, fling them apart?

• “What force could possibly be great enough to move a continent?”

Revisiting the magnetic field

• Convection in the outer core generates an electric current that drives our magnetic field

• This field can reverse

  • 12 times in 4 million years

  • 171 times in 76 million years

Magnetic Declination

• Angle between magnetic north and geographic (true) north

• Boone = 7.62 W

Magnetic Signal is recorded in the rock record

1. Sediments

   1. Depositional remanent magnetization

2. Cooled Lavas

   1. Thermoremanent magnetization

Paleopoles - previous position of Earth’s Magnetic Poles

• If we assume the continents are stationary, we should see the path of polar wander stay in the geographic North Pole region

Something is very wrong… if plates are stationary, what should paths do?

Magnetic Anomaly

• The difference between the expected strength of the Earth’s Magnetic Field at a certain location and the actual measured strength of the field at that location

Bathymetry

• The study of underwater topography of water bodies (oceans, rivers, lakes)

• In World War 2, the military used SONAR to locate enemy vessels and image the sea floor

  • S Sound

  • O

  • N Navigation

  • A And

  • R Ranging

Mid Ocean Ridge

• A submarine mountain belt that forms along a divergent oceanic plate boundary

• MOR

• Area of extension

• Mantle is very close to the surface

Earthquakes coincide with MORs

If new crust forms at mid-ocean ridges -> Old crust must be consumed elsewhere

How do we know that the seafloor is spreading over time?

• Apply magnetism to the seafloor

Seafloor Spreading

• Gradual widening of an ocean basic as new oceanic crust forms at a mid-range ridge axis and the moves away from the axis

Evidence for seafloor spreading

1. Sediments got older away from the ridge axis

2. Sediment on top of the crust gets thicker, further away from the ridge

3. Oldest oceanic crust is only about 200 Ma

This was the key evidence needed for Wegener’s Continental Drift Theory (new name needed though!)

• Spreading Rate:

  • Atlantic = 2 cm per year

  • Pacific = 10 cm per year

Think back to the structure of the Earth:

• Crust = <1%

Buoyancy - an object will float when the mass of the fluid displaced is equal to the mass of the object

It’s the same for continental crust

• Isostasy - buoyancy force pushing the lithosphere equals the gravitational force pulling lithosphere down

• Dense asthenosphere is displaced by lithosphere/crust above it

Recap

• Now we know about:

  • The idea of continental drift

  • Seafloor spreading

  • Two types of crust

Plate Boundaries

• The border between two adjacent lithospheric plates

• There are three types of plate boundaries that are defined by the way one plate moves relative to another

1. Divergent

   1. Two plates move apart from one another

      1. Mid-ocean ridge

      2. Continental rifting

   2. Divergent Plate Boundaries always create new crust.

      1. What rocks make up this new crust?

         1. Basalt

            1. Pillow Basalt

   3. As the seafloor ages, the lithospheric mantle thickens

      1. The seafloor surface gets deeper

   4. Continental Rifting

      1. Divergent plate boundaries involving only continental crust at the beginning of the extensional process

         1. Examples:

            1. Basin and Range (Nevada)

            2. East African Rift

            3. Red Sea

            4. Rio Grande (New Mexico)

2. Convergent

   1. Two plates move towards each other

      1. Continent/continent

      2. Continent/oceanic

      3. Oceanic/oceanic

   2. Sometimes consume old crust

   3. Usually creates mountain ranges

      1. Continent/continent collisions form mountain ranges like the Appalachians

      2. Continental/oceanic

         1. Results in a subduction zone where one plate slides under the other

         2. Creates a volcanic arc

         3. Subducted crust melts at depth and creates new crust via volcanic mountain range

         4. Examples:

            1. Sierra Nevada

            2. Andes

            3. Sierra Madres de Chiapas

      3. Oceanic/oceanic

         1. One oceanic crust plate will subduct under the other oceanic plate

         2. The plate that subducts is:

            1. Older

            2. Colder

            3. Denser

            4. Deeper

         3. Examples: Japan, Alaskan SW Peninsula

   4. Features of Convergent Plate Boundaries

      1. Earthquakes - Wadati Benioff Zone

         1. Band of earthquakes in a downgoing plate

         2. Surface to depth of 660km at the lower mantle boundary

         3. Plates can go deeper than 660 km

      2. Accretionary Prism - wedge-shaped mass of sediment and rock scraped off the top of the downgoing plate and accreted onto the overriding plate at a convergent plate boundary

      3. Basins

         1. Back-Arc Basin - (marginal sea) form between an island arc and main continent due to localized extension

         2. Fore-Arc Basin - area between trench and associated volcanic arc

         3. Trench - deep elongate trough bordering a volcanic arc. Defines the trace of a convergent plate boundary

            1. Examples: Mariana Trench

               1. Challenger Deep - Deepest place on earth

               2. 10.984 km deep!

                  1. 6.8 miles

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County of the Day: Rutherford

• Garnet - mineral that can be many different colors (red and green are common)

• Very hard (6.5-7.5), used as an industrial abrasive like diamond

• Found in granitic gneiss on Marlin’s Knob

3. Transform Boundaries

   1. Two plates slide past each other

   2. Motion is predominantly horizontal

   3. Fracture Zones - a narrow band of vertical fractures in the ocean floor

      1. Fracture zones lie roughly perpendicular (@ right angles) to a mid-ocean ridge

      2. The actively slipping part of a fracture zone is a transform fault

   4. Special Cases

      1. Triple Junctions - Three plates intersect

         1. Examples: Indian Ocean, San Francisco

      2. Hot Spots - isolated volcano not caused by movement at a plate boundary, but by melting at a point locality (top of a mantle plume)

Margins - where continental crust meets oceanic crust

Active Margin

• Margin coincides with a plate boundary

  • Example: Coast of California

Passive Margin

• Margin does not coincide with a plate boundary

  • Example: East Coast of US

Convergent plate boundaries + two continental crust plate = Orogeny - mountain building, the process of forming a mountain belt

With orogenies, we are going to think about:

• Uplift - raising of the surface of the crust

• And

• Deformation - process by which rocks bend, break, or flow in response to stress

Deformation produces:

• Joints

• Faults

• Folds

• Foliation

  • All geologic structures

2 types of deformation

1. Brittle Deformation - cracking and fracturing of a material subjected to stress

   1. Think glass shattering

   2. Breaking a plate

2. Plastic Deformation - (ductile deformation) the bending and flowing of a material subjected to stress (without cracking or breaking)

   1. Think squishing dough

   2. Shaping clay

   3. Stretching rubber bands

2/4

Mechanisms of Deformation: #1 Bending

• Bending is a type of plastic deformation

Law of Original Horizontality

Geologic Structure Produced: Folds

• Fold - a bend or wrinkle of rock layers

• Caused by a compressive force

Anticline - a fold with an arch-like shape in which the limbs dip away from the hinge or fold axis

Syncline - a trough shaped fold whose limbs dip toward the hinge

Synclines and Anticlines can occur together

Other fold types:

• Monocline - fold in which one limb is much steeper than the other. Monoclines resemble a carpet draped down over a stair step.

• Dome - folded or arched layers with the shape of an overturned bowl

• Basin - fold shaped like a right-side-up bowl

  • Opposite of a dome

• Plunging fold - fold with a tilted hinge

  • Any type of fold can plunge

Mechanisms of Deformation: #2 Breaking

• Breaking is a type of brittle deformation

Joints - naturally formed cracks in rocks

Columnar Jointing - type of fracturing that yields roughly hexagonal columns of basalt. Columnar joints form when a dike, sill, or lava flow cools

Fault - a fracture on which one body of rock slides past another

• The direction of motion depends on the tectonic forces on the rocks

Dip-Slip Fault - a fault where sliding occurs up or down the slope (dip) of the fault

• Two pieces of rock on either side of the fault

• Hanging Wall

• Footwall

Normal Fault

• Footwall is up relative to the hanging wall.

• Formed in extensional regimes

• Think:

  • Divergent Plate Boundaries

  • Two rocks pulling apart

Reverse Fault

• The hanging wall is up relative to the footwall

• Formed in compressive regimes

• Think:

  • Convergent plate boundaries

  • Mountain building

Thrust Fault

• Similar to a reverse fault but the angle of the fault is low

  • Around 15 degrees

• Hanging wall is up relative to footwall

• Formed in compressive regimes

• Think:

  • Convergent plate boundary

  • Mountain building

F.U.N H.U.R.T.

Footwall Up Normal Hanging (Wall) Up Reverse (or) Thrust

• All three faults are types of dip-slip faults

Strike Slip Faults

• Strike-slip fault - a fault where one block slides horizontally past another with no vertical motion

Oblique-Slip Fault

• Oblique Faults - a fault where blocks move diagonally relative to each other with both vertical and horizontal movement along the fault plane

• Can occur in compressive or extensional regimes!

Other brittle geologic structures

• Veins - a seam of minerals that forms when dissolved ions carried by water solutions precipitate in rocks

• Form in open joints and fractures

• Under 10 cm in width

• Veins can intersect

• Most veins in WNC are quartz

• Other minerals in veins include calcite and galena

Veins can form in multiple generations

#3 Shortening

• Compression - a push or squeeze felt by a body

• Plastic deformation

• Compressional forces

#4 Stretching

• Tension - a stress that pulls on a material and could lead to stretching

• Plastic deformation

• Extensional forces

#5 Shearing

• Shear stress - a stress that moves one part of a material sideways past another part

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County of the Day: Moore

Massive and radiating pyrophyllite- Al2Si4O10(OH)2

Pyrophyllite is a micaceous mineral formed as the result of the relatively low grade metamorphism of aluminum-rich rocks. It can also form as a hydrothermal replacement of aluminous materials such as feldspars. The mineral may be in fine-grained aggregate and is easily mistaken for other phyllosilicates. - Wisconsin Geological Survey

Locality in Moore Co. accompanied by pyrite

Two Extra Credit Opportunities!

Showing of Apollo 11 in RSW 293 tonight at 7pm. Fill out the form on asulearn for extra credit movie

Foliation- layering formed as the consequence of the alignment of mineral grains or a compositional banding in a metamorphic rock

• Type of plastic deformation

• Stretching + shear stress

Requirements for foliation:

• 1. Differential pressure

• 2. Minerals with a preferred orientation

  • Think ovular, bladed, and tabular shapes

Mountains related to subduction

• Oceanic crust plate will subduct under a continental crust plate

Mountains related to collision

Continental crust plate converges with another continental crust plate

Combination of subduction and collision? Subduction -> collision?

• Sometimes, collisions begin as subduction zones. As oceans and seas close, that brings other pieces of continental crust to the convergent plate boundary

• The attachment of volcanic island arcs and other “microcontinents” is called accretion

Mountains related to continental rifting?

What types of rocks do we make during orogenies?

Structural Geology on Maps!

We look at rocks in place in two ways:

1. Geologic Maps- a map showing the distribution of rock units across a region

   1. Can be a small area or large

      1. Full globe

      2. Town of Boone

2. Cross Sections- depiction of contacts in the subsurface as represented by their traces on an imaginary vertical slice into the earth

   1. Show much smaller areas

USA Geologic Map from the Library of Congress

Published circa 1870

How do geologists make geologic maps and cross sections?

By measuring real rocks!

1. Find Bedding

2. Measure Strike

3. Measure Dip

4. Draw on a map!