EESC 1000 Exam 1

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Geocentric model

Earth-centered model of the universe; associated with Ptolemy (85–165 CE); all planets/stars were thought

Heliocentric model

Sun-centered model; proposed by Nicolaus Copernicus (1473–1543) in De revolutionibus orbium coelestium; this is the correct model.

Key figures after Copernicus

Galileo Galilei, Johannes Kepler, and Sir Isaac Newton provided observational and mathematical support confirming the heliocentric model.

Fuel of the Sun

Hydrogen fusion, occurring in the Sun’s core at ~10 million K, converts H into He and releases energy.

Sun’s core vs. surface temperature

Core: ~10 × 10⁶ K (site of fusion); Photosphere (surface): ~5,800 K — the core is far hotter because that’s where fusion occurs.

Star vs. galaxy

A star is a single self-luminous ball of plasma (like the Sun); a galaxy is a massive, gravitationally bound

collection of billions of stars (e.g., the Milky Way)

Location of our Sun

The Sun is one of >300 billion stars in the Milky Way, a spiral galaxy; the Sun sits near the outer edge of

one spiral arm.

Scale of the universe

The visible universe may contain up to ~1 trillion (10¹²) galaxies.

Star classification variables

Stars are grouped by (1) effective/surface temperature and (2) luminosity (usually normalized to

the Sun’s luminosity, L☉).

Three groups of planets

(1) Terrestrial (inner) planets, (2) Gas giants, (3) Ice giants (outer/Jovian planets).

Terrestrial planets

Mercury, Venus, Earth, Mars; rocky shells with solid cores; no rings.

Gas giants

Jupiter, Saturn; composed mostly of hydrogen and helium; primarily gaseous/liquid but with solid cores; many

moons and rings.

Ice giants

Uranus, Neptune; consist mostly of frozen water, CO₂, and methane; have moons and rings.

Definition of a planet

(1) Roughly spherical, (2) orbits a star, (3) has cleared/incorporated most other objects in its orbital

neighborhood.

Orbital plane

All planetary orbits lie approximately in the same plane around the Sun; orbits are elliptical, not circular.

Habitable zone

The distance range from a star (for our Sun,

~0.8–2.5 AU) where conditions could allow liquid water to exist.

Moon (as a general term)

A rocky/icy satellite that orbits a planet (e.g., Io and Ganymede orbit Jupiter).

Asteroid

Relatively small rocky or metallic object (1 cm–~1000 km) that orbits the Sun; most occur in the asteroid belt

between Mars and Jupiter.

Trans-Neptunian Objects (TNOs)

Icy bodies orbiting the Sun beyond Neptune; debris of frozen H₂O, CH₄, NH₃; includes dwarf

planets (Pluto, Eris) and comets.

Comet

“Snowball” of frozen gases, rock, and dust; short-period comets come from the Kuiper Belt, long-period comets come

from the Oort Cloud.

Kuiper Belt

Region beyond Neptune containing icy debris and dwarf planets (including Pluto); source of most short-period

comets.

Oort Cloud

Roughly spherical cloud of icy debris far beyond the Kuiper Belt; source of long-period comets.

Meteoroid

A small “space rock” (fragment of an asteroid or comet) still floating through space.

Meteor

A “space rock” that has entered Earth’s atmosphere and burns up (“shooting star”).

Meteorite

A “space rock” that survives entry and hits a planet’s surface (did not burn up entirely); can form a meteorite crater.

Doppler effect (general)

the change in observed wavelength/frequency of a wave caused by relative motion between source

and observer.

Doppler effect for light — blue shift

Object moving toward observer → wavelength shortens, frequency increases.

Doppler effect for light — red shift

Object moving away from observer → wavelength lengthens, frequency decreases

What red shift tells us about the universe

Edwin Hubble discovered that virtually all distant galaxies show red shift,

meaning they are moving away from us at great velocity → the universe is expanding.

Big Bang theory

The idea that the universe began ~13.8 billion years ago (Ga) from an infinitesimally small, extremely

hot/dense point that exploded and has been expanding ever since.

Nucleosynthesis

The formation of chemical elements inside stars; first-generation stars fused H into He; heavier elements

form during later stages of stellar life cycles.

How elements are released into space

Via stellar wind (e.g., solar wind) during a star’s life, or catastrophically during a

supernova explosion (death of a massive star).

Planetary nebula

A cloud containing all chemical elements (younger material than a supernova); tiny ice/dust particles

condense and grow, eventually becoming large enough for gravity to pull them together.

Formation of the solar system (order of events)

Nebula → protoplanetary disk → planetesimals → protoplanets → planets

(~4.57 Ga) → Moon formed by a giant collision (~4.5 Ga) → cooling.

Frost line

The boundary in the protoplanetary disk separating refractory (rocky, closer to Sun) material from volatile (icy,

farther from Sun) material — explains why terrestrial planets formed inside and gas/ice giants formed outside.

Earth’s layered structure (by composition)

Crust (thin, silicate rock) → Mantle (thick, silicate rock) → Outer Core (liquid Fe)

→ Inner Core (solid Fe); Earth’s radius ≈ 6,371 km

Compositional layer boundaries

Crust/mantle boundary ~7–70 km depth; mantle/outer core (core-mantle boundary) ~2,900

km; outer core/inner core ~5,150 km

Layers by composition vs. by properties

Composition (chemistry): crust, mantle, outer core, inner core. Properties

(mechanical behavior): lithosphere (rigid) and asthenosphere (plastic) — these cut across compositional boundaries.

Lithosphere (definition)

Rigid outer shell = crust + the rigid (uppermost) part of the mantle.

Asthenosphere (definition)

“Soft”/plastic mantle layer below the lithosphere; can deform over long time periods without

breaking, because it is close to its melting point.

Geothermal gradient (geotherm)

The rate of change of temperature (T) with depth in the Earth.

Melting curve vs. geothermal gradient

The melting curve shows the T at which Earth materials begin to melt at a given depth. If actual

T (geotherm) > melting T, material is liquid (this is why the outer core is liquid). In the asthenosphere, T ≈ melting T (nearly

melting, hence “plastic”).

Sources of Earth’s internal heat #1: Planetary accretion

Kinetic + gravitational energy from accreting material produced

primordial heat; caused internal melting and differentiation (separation into core/mantle by density).

Sources of Earth’s internal heat #2: Natural radioactivity

Heat-producing radioactive isotopes, concentrated in the crust,

are responsible for ~50% of surface heat flow; this is why the geothermal gradient is much steeper in the crust than in the

mantle.

Crust composition (dominant elements)

Oxygen (46%) and Silicon (28%) dominate by weight; also Al, Fe, Ca, Mg, Na, K.

Dominant crustal rock types

Granite (continental crust) and Basalt (oceanic crust).

Dominant mantle rock type

Peridotite — accounts for most of Earth’s volume; compositionally similar to stony meteorites.

Continental crust thickness

25–70 km; thicker beneath mountain belts, thinner below continental rifts.

Oceanic crust thickness

7–10 km; composed of basalt.

Why Earth has a magnetic field

The liquid, electrically conductive outer core (moving iron) generates the magnetic field via

a moving-electric-conductor (geodynamo) effect, producing a magnetic dipole.

Consequences of Earth’s magnetic field

Creates the magnetosphere, which deflects the solar wind (charged particles from

the Sun); Van Allen belts trap charged particles; protects life on Earth from dangerous radiation.

Aurora (Borealis/Australis)

Charged particles that get past the Van Allen belts are funneled along magnetic field lines toward

the poles, collide with atmospheric O₂/N₂ molecules, and release energy as light

Stony meteorites

Fragments of asteroids that were too small to ever differentiate into a core + mantle; give indirect evidence

about mantle (peridotite) composition.

Iron meteorites

Fragments of larger, differentiated planetesimals/asteroids that did separate into a metallic core and rocky

mantle; give indirect evidence about the core’s (iron) composition.

Alfred Wegener

German meteorologist (1880–1930) who proposed continental drift in 1912 based on the matching fit of

continental coastlines (like a jigsaw puzzle); met strong opposition; published book in 1920; vanished on a Greenland expedition.

Pangaea (“Urkontinent”)

The single supercontinent Wegener proposed once existed, surrounded by the global ocean

Panthalassa; existed near the end of the Paleozoic era (~280–260 Ma).

Five lines of evidence for Pangaea

(1) Shape/fit of continents, (2) location of past glaciations, (3) distribution of past climate

belts, (4) distribution of fossils, (5) location of matching geologic units (mountain belts).

Glacial till & striations as evidence

Poorly sorted glacial sediments (till) and scratch marks (striations) from Late Paleozoic

glaciation occur on continents now far from the poles and even near the equator — only makes sense if those continents were

once joined together near the pole.

Past climate belts as evidence

Coal deposits (tropical forests), desert/salt-flat deposits, and fossil reefs (subtropical) are

found in patterns that only make geographic sense if the continents were arranged differently (as Pangaea).

Fossil evidence for Pangaea

Land-dwelling/coastal species (e.g., Mesosaurus, Cynognathus, the plant Glossopteris) are

found on continents now separated by oceans they could not have crossed → those continents must once have been joined.

Geologic units as evidence

Matching mountain belts (e.g., the Appalachians) line up across continents that are now

separated, showing they were once continuous.

Bathymetry

The measurement/mapping of ocean-floor depth and topography (originally via sonar/echo-sounding: a sound

pulse is sent from a ship, bounces off the seafloor, and returns).

Topography of the ocean floor (key features)

Continental shelf → continental slope/margin → abyssal plain → mid-ocean

ridge (MOR, the highest topography, running through ocean basins) with associated fracture zones.

Evidence ocean floor is younger than continents

Sediment on the seafloor is far too thin to represent Earth’s whole

history, and sediment gets thicker and older with distance from the mid-ocean ridge → ocean floor must be actively forming

(younger than continents) and heat flow is higher near the ridge

Declination (D)

The angle between a longitude line (geographic north) and the direction a compass needle points (magnetic

north) — because magnetic north ≠ geographic north.

Inclination (I)

The angle between a magnetic field line and Earth’s surface; I = 0° at the magnetic equator, I = 90° at the

magnetic pole; tells you the latitude (distance from magnetic pole) at which a rock formed.

Magnetic dipole of a rock

When a rock forms, its magnetic minerals align with Earth’s magnetic field at that time and place,

“freezing in” a record of that field’s declination and inclination.

Paleopole

The apparent position of the magnetic pole at the time a rock formed, determined from that rock’s magnetic dipole

(D and I) — the basis of paleomagnetic studies.

Apparent polar wandering

Each continent’s rocks show their own apparent path of the magnetic pole moving over time.

Since the pole doesn’t actually move differently for each continent, the different apparent paths mean the continents themselves

moved relative to one another — direct proof of continental drift.

Reversed polarity

Periodic flips in Earth’s magnetic field, where magnetic north and south swap; the Earth itself does not turn

upside down, only the field polarity reverses.

Magnetic anomaly

A local deviation (stronger or weaker) in measured magnetic field strength compared to today’s field,

caused by the magnetization of the underlying rock.

Positive vs. negative magnetic anomaly

Positive anomaly = seafloor rock has the same polarity as today’s field (field

strengths add → stronger signal). Negative anomaly = seafloor rock has the opposite (reversed) polarity (fields subtract → weaker

signal).

Magnetic stripes on the seafloor

Seafloor spreading produces alternating parallel bands of normal/reversed polarity rock

that are symmetric on either side of the mid-ocean ridge axis; stripe width is proportional to how long that polarity lasted — this

pattern proved seafloor spreading.

Continental vs. oceanic crust

Continental: thick (25–70 km), granitic, relatively low density. Oceanic: thin (7–10 km),

basaltic, relatively high density.

Continental vs. oceanic lithosphere thickness

Continental lithosphere: 150–200 km thick. Oceanic lithosphere: <100 km

thick.

Crust/Mantle boundary (“Moho”)

The Mohorovičić discontinuity; a sharp material (compositional) boundary between crust

and mantle rock (density of mantle rock > density of crustal rock); the Moho mirrors Earth’s surface topography (deeper under

mountains).

Lithosphere/Asthenosphere boundary

A gradational boundary based on rigidity/temperature (not composition — both are

made of the same mantle rock, peridotite). Roughly defined by the ~1280°C isotherm: below this T, rock is rigid (lithosphere);

above it, rock is plastic (asthenosphere).

Key difference: Moho vs. lithosphere-asthenosphere boundary

Moho = sharp compositional (crust vs. mantle) boundary.

Lithosphere/asthenosphere boundary = gradational mechanical (rigid vs. plastic) boundary within the mantle.

Buoyancy

The upward force on an object caused by displacement of a denser surrounding medium; a floating object (e.g., an

iceberg) sinks until the mass of the entire object equals the mass of the fluid it displaces (Archimedes, 212 BCE).

Isostatic equilibrium (isostasy)

The balance reached when a less dense lithosphere “floats” on the denser, plastic

asthenosphere — analogous to how a ship floats on water; buoyancy depends on both the density and the thickness of the

lithosphere.

Isostasy and elevation

Because continental crust is less dense than oceanic crust, continents sit at higher elevation; young,

warm oceanic lithosphere near a mid-ocean ridge is less dense (higher) than old, cold oceanic lithosphere farther away (lower,

e.g., abyssal plains).

Isostasy and mountain roots

Tall mountain ranges have deep, low-density “roots” that extend down into the mantle to

support/buoy up their weight (like the submerged part of an iceberg).

Isostatic rebound (glacial)

When an ice sheet grows, its weight depresses the crust/lithosphere into the asthenosphere;

when the ice melts/retreats, the crust slowly rebounds (rises) back toward its original position as asthenosphere flows back in

(e.g., Scandinavia, the Alps).

Isostasy and erosion/mountain building

As mountains erode, the removed mass causes uplift (isostatic rebound) at the

mountain while the deposited sediment causes subsidence at the site of deposition — an ongoing feedback.

How plate boundaries are recognized

Earthquake locations define narrow, continuous belts on a map — these belts mark

the boundaries of rigid lithospheric plates.

Plate boundary vs. continental margin

A continental margin is the boundary between continental and oceanic crust within

the same plate; a plate boundary is the edge between two separate tectonic plates. They are not always the same thing.

Active continental margin

A continental margin that is a plate boundary (e.g., subduction zone) — associated with

earthquakes and often volcanism/trenches.

Passive continental margin

A continental margin that is not a plate boundary (e.g., the U.S. East Coast) — no significant

earthquake activity, gently sloping shelf, part of continuous continental + oceanic lithosphere of the same plate.

Three types of plate boundaries

(1) Divergent, (2) Convergent, (3) Transform.

Divergent boundary

Plates move apart; new lithosphere is created; lithosphere thickens away from the axis; occurs at mid-

ocean ridges (oceans) or continental rifts (continents).

Divergent — oceanic (mid-ocean ridge)

Magma rises at the ridge axis, creating new oceanic crust; produces pillow lava and

hydrothermal vents (“black smokers”).

Divergent — continental (rifting)

Continental lithosphere thins/stretches as asthenosphere rises beneath it, forming a rift

valley (e.g., East African Rift); if rifting continues, the continent breaks apart and a new mid-ocean ridge forms.

Convergent boundary

Plates move toward each other; one plate is typically subducted (consumed) beneath the other;

subduction zone = site of consumption; associated with earthquakes and melting.

Convergent — ocean/continent

Denser oceanic lithosphere subducts beneath continental crust, forming a trench and a

continental volcanic arc (e.g., Andes).

Convergent — ocean/ocean

One oceanic plate subducts beneath another, forming a trench and a volcanic island arc (e.g.,

Japan, Aleutians).

Convergent — continent/continent

Since neither continental plate is dense enough to fully subduct, oceanic lithosphere

between them subducts first, then the continents collide, producing a large mountain belt (e.g., Himalayas) without ongoing

subduction beneath it (detached oceanic lithosphere).

Transform boundary

Plates slide horizontally past one another; no new crust is created and no plate is consumed (no

melting); still produces frequent, often large, earthquakes (e.g., San Andreas Fault).

Fracture zones vs. active transform faults

The actively slipping segment between two offset ridge segments is the

transform fault (seismically active); the scars extending beyond it on either side (no longer at the plate boundary, moving

together) are fracture zones (not seismically active).

Hot spot

A relatively stationary source of magma (mantle plume) rising from deep in the mantle (near the core-mantle

boundary), independent of plate boundaries.

Why hot spots trace plate motion

Because the hot spot itself stays fixed while the lithospheric plate moves over it, it leaves

a trail of progressively older volcanoes/islands in the direction the plate has moved (e.g., the Hawaiian-Emperor seamount chain

gets older away from the active hot spot); a bend in the trail records a change in plate motion direction (e.g.,

~40 Ma for the

Pacific plate).