August 19, 2015
Earth in Space
• Population density- populations tend to form along coast lines
because easy to make a living and transport goods, etc.
• Lights at night show that there are differences in comparing
populations and energy usage because although in US and Europe
the populations are less dense, however we use more energy and
density reflects energy and affluence, not just population.
• Earth is one the 4 relatively small planets. All planets travel in the
same direction and most rotate in the same direction. They orbit
close to the ecliptic, meaning they rotate close to the sun.
• Dust-rich disks are common in the universe, which provides
evidence for a model. (Andromeda galaxy)
• The “terrestrial” planets are the four inner planets
o Mercury: Density of 5.4 gm/ cm -3. Doesn’t have an
atmosphere. Surface is densely cratered because of what is
thought to be done by impacting bodies. Such surfaces
represent the oldest surfaces in the solar system. We don’t
have any samples from mercury so estimated age.
o Venus: 96% Co2 atmosphere. You can’t see any features on
the surface with regular camera/light because of clouds. If
you have the photographic machine that can penetrate the
surface using radiation you can then see the surface. Not a
ton on craters, which makes us think that Venus isn’t super
old. Using Magellan measurements to create topographic
map of Venus. Similar in size and density to earth. Surface
atmosphere P = 100 x that of earth. Surface T= 475 C and
water boils at 100 C
o Mars: 95% CO2 in the atmosphere. Surface pressure= .006 x
Earth. Average surface temperate = -60 C and water freezes
at 0 C. Surface of Mars varies from relatively young to
relatively old because some places with nothing and some
places with many craters. Clear evidence for the existence of
water because flood paths. And there are layered
sedimentary rocks that look like those on earth created by
wind and water. Mars has 2 rovers working on it now.
Curiosity is currently working there after landing August 2012.
It landed on the equator because weather is milder and the
rover is solar powered and there was the most sun there. o Our Moon: No atmosphere. Surface has a lot of impact
craters including very large craters. Filled with lava flows. In
the center of the largest impacts, a mountain range forms.
o Craters on Earth: Present but not common. Only about 200
known craters on Earth. Many of the craters have eroded and
because of the active surface (plate tectonics) they have been
o Earth: 78% N2, 21% O2, <4% H2O, and .035% CO2.
Oxygen is produced from living things and is not a constant.
Note that CO2 is a trace constituent in spite of its important
effect on climate. Coal, fossils, and the ocean have a lot of
CO2 saturated in them. Surface T= 20 C. Atmosphere is O2
rich and CO2 poor because earth has a mechanism to remove
CO2. The atmosphere reflects Plant production of oxygen August 21, 2015
Previous review points:
• Relentless population growth contributing cause of environmental
• Solar system: Planets orbit sun in same direction + about the same
plane consistent with nebula model of rotating cloud of dust
planets around proto sun
• Terrestrial (rocky planets): Mercury, Venus, Earth (moon), Mars
• Mercury, Moon: old, densely cratered surface, no atmosphere
• Venus: Young surface, surface temperature is about 475 C
• Mars: Young to old surface, evidence for water (floods, rivers),
Surface temperature is about -60 C
• Earth get oxygen from photosynthesis: 6 CO2 + 6H2O + Light
Sugar + 6 CO2
• C-Banks: Carbonate rocks, coal, petroleum, natural gas, plants
Pressure CO2 N2 O2 SO2 H2O Ar
Venus 100x Earth 96% 4 - .015 - -
Earth .035 78 21 Traces <4 Trace
Mars .006 x Earth 95 3 .13 ? - 2
What current additions to the atmosphere exist?
• Main addition are volcanic gases with the two common being water
• Volcanoes are critical evidence that the interior of the earth is quite
• Hot springs also reflect internal heat of the earth
• Earth scientists have the “Geothermal gradient” which is the change
in temperature with depth.
• Temperature increases all the way to the center of the earth
• Surface temperature of the sun is about 5500 C
• Average depth of the oceans: 2.3 miles
• Average height of the continents: 800 ft
• The continental shelf is considered to be part of the continent.
Therefore, the actual edge of a continent is called the continental
• Mid-ocean ridges (ocean mountain ranges) are one of the more
distinct topographic features.
• Terrestrial ranges tend to grow long and narrow.
• A trench is on the convex (outside of the curve) side of the arc in a
volcanic island arc and deep-sea trench relationship. Earth’s Topography
• Continent/ocean dichotomy, i.e. bimodal distribution of elevations
• Mid-Ocean ridge system: 80,000 km long, 1500-2,500 km wide, 2-3
km above abyssal plain
• Long, narrow continental mountain ranges
• Deep-sea trenches adjacent to arcs of volcanic islands.
• Is like an avocado
• Divided into crust, mantle, and core (inner and outer core)
• The densest material is at the center
• The mantle is softer and flows more than the core (like the avocado
vs. the seed)
• Earth’s core is thought to be similar to the material that makes up
iron meteorites: 90% metallic iron (Fe) and 10% metallic nickel (Ni)
• The densest crust underlies the ocean basins August 24, 2015
• Current addition to atmosphere: Volcanic gases H2O and CO2
• Earth’s interior is hot as indicated by volcanoes and hot springs
• Geothermal gradient is about 20-25 C/km
• Center of Earth at about 5500 C (Same as sun’s surface)
• Earth’s key topographic features are:
o Continents: average elevation of 500 m
o Ocean Basins: Average depth of 4.5 km
o Mid ocean ridges: 2-3 km above the ocean floor, circles the
o Volcanic arcs: the deep sea trench is always on the outside
o Deep sea trenches ^
o Continental mountain ranges are long and narrow
• Bimodal distribution of elevations is unique to Earth
Chapter 2: Mineralogy and Petrology (Study of rocks)
Element vs. mineral vs. rock
• Element: found on the periodic table (number= atomic number =
number of protons)
o Proton, neutron, and electron
o Most elements do not occur as a pure substance in nature
o All atoms of material have the same number of protons
• Mineral: Can be identified on the basis of crystal shape, density,
chemical composition, atomic structure, hardness, and many other
physical properties. To be a mineral, it has to be natural, solid, and
crystalline (Atoms are arranged in a regular, repeating order). In
most minerals the atoms are bonded ionically, meaning by attraction
between + and – charges. Positive ions are cations and negatives
are anions. Most minerals are made up of some combination of
elements in rows 2, 3, and 4 of the periodic table. The overall
structure of the mineral is electrically neutral.
o *Know the elements Main mineral groups: Oxides, Sulfides,
Halides, Carbonates, Hydroxides, Native Elements (Gold,
silver, graphite, diamond), and Sulphates
o Minerals to know!
▪ Quartz: SiO2- A silicate, very common, rock-forming
mineral. Persists in the surface environment.
▪ Feldspar: (Na, K) AlS3O 8- Pink to white grains in rock in
picture. A Silicate, most abundant mineral in Earth
crust. Weathers away rapidly to form soils and clays. ▪ Fe-MG silicates: (Mg,Fe) 2SiO4-Dark-colored minerals of
common rocks, weather rapidly
▪ Pyrite: FeS 2– A sulfide, various sulfides are common
ore minerals, commonly known as fools gold, weathers
readily, the culprit in acid rain and acid mine drainage,
produced sulfuric acid when weathered or burned.
▪ Calcite and aragonite: CaCO 3– carbonates, with same
chemical formula there is a different atom arrangement.
Will slowly dissolve in fresh water but precipitates from
shallow, warm seas (Bahamas) and shells & corals are
made of these carbonates- are carbon sinks or “banks.”
▪ Table salt or Halite: NaCl- Generally forms from
evaporation of sea water.
▪ Magnetite: Fe 3O 4– Oxide, naturally magnetic, crucial to
plate tectonic theory August 26, 2015
• Earth segregated by density:
Core Fe-Ni Metal 12 gm/cm^3
Mantle Fe-Mg Silicates 4 gm/cm^3
Ocean Crust Fe-Mg Silicates > feldspar 3 gm/cm^3
Continental Crust Feldspar + quartz > Fe-Mg 2.7 gm/cm^3
• Earth materials:
o Minerals: natural, solid, crystalline (repeating, 3 dimensional
o Cations: Positive charges ions
o Anions: Negative charged ions
o Both ^ Free ions common in fluids, e.g. ocean water. They
balance charges in minerals- electrically neutral
• Minerals classified by anions:
Silicates SiO 4 Most common minerals
Carbonates CO3 -2 Contain C
Sulfides S Common metal ores
Halides Cl or F - Salt (halite) is one
Oxides O Rust is an example
Hydroxides OH - Contain water
Sulfates SO 4 Gypsum is one
Native elements Pure Au, Pt, diamond, graphite
• Quartz- is stable, persists in the Earth’s environment
• Feldspar- Most abundant in crust, unstable on Earth’s surface
(reacts with weather)
• Fe-Mg Silicates: Unstable, black
• Calcite: One of the big carbon banks!
• Magnetite: Magnetic
• Halite: Salt
• Pyrite: Sulfide, Unstable, when it weathers it gets oxidized and end
up with sulfuric acid.
Mineral Stabilities • Where is ice stable, or where does it form in terms of pressure and
temperature? Does ice form at the same T in Athens and Denver?
• As pressure increases, water will freeze at a slightly higher
temperate (aka 33 instead of 32). As Pressure increases, water will
boil at a slightly lower temperature (for example, 98 degrees vs.
• Diamond is not stable on Earth’s surface- yet we still have it and
they persist of many life times. They are stable however in the earth
interior- still doesn’t answer how we can have them on the exterior
• Pressure in the earth increases at a constant rate around the globe
with dept. P=Density x gravity x depth
• Deepest mine on earth: 3.5 km and T of 55 C and P of 920
atmospheres. Temperature is over 100 degrees, which limits a
workers time to about 10 minutes in the cave.
• Measurement in deep mines and drill holes indicate that T typically
increases at a rate of 25 C/km. This is called the geotherm.
• If pressure and temperature drop rapidly, a “metastable” mineral can
be preserved because at low temperature, atoms have trouble
rearranging themselves. So if volcanism brings diamonds rapidly to
the surface and cooling is quick, diamonds are preserved. Even
when we think it’s hot, to an atom it’s typically cold and therefore
doesn’t feel like moving around and changing it’s arrangements.
What is a rock?
• Composed of numerous grains of one or more minerals cemented
together or having an interlocking texture like a jigsaw puzzle.
• Igneous rocks preserve minerals and textures formed at high T, and
sometimes P August 28, 2015
• Stable: Mineral will remain as in indefinitely (quartz is the only
common mineral that approaches this state)
• Metastable: Mineral will react with water, O2.. to form new minerals
but this process may take more than 1,000,000,000 years. An
example is a diamond
• Temperature: Increases at a rate of 20-25 C/km in most areas of
continents (Athens is about 18 C/km
• Pressure: increases at a rate of .1 Gigapascals/km
• Hurricanes rotate counterclockwise
Rocks come in 3 flavors
• Igneous: crystallized or frozen from a very high temperature viscous
o Two kinds- Volcanic crystalize on the Earth’s surface and
Plutonic freeze in the Earth’s surface
o If freezing occurs very quickly, a black glassy matrix forms
o Volcanic rocks give us a “snapshot” of magmas which consists
of a viscous liquid (melt) + crystals + gas (which may or may
not be dissolved in the melt).
o The freezing process is analogous to the freezing of water or
the growth of a snowflake
▪ Except the number of crystalizing forces is 3 or 4 vs. 1
• Sedimentary: formed at or near the earth’s surface by accumulation
of sediments or chemical precipitates
o Come in 3 flavors-
▪ Clastic sediments: form by the accumulation of the
sediment (sand, mud, gravel) transported by water,
wind, and ice. Example is sandstone formed by the
accumulation and lithification (cementation) of the sand
grains. The grains are held together by cement,
generally calcite (CaCO3) or silica (SiO2). The cement
is precipitated by groundwater after the sediments are
buried by younger sediment. Recognizable features
such as ripple marks and layering. Mars has layered
marks but we do not know what from
▪ Biochemical sediments: include the peat (organic
matter) that accumulates in swamps and ultimately is
changes to coal. Limestone, made of CaCO3, can be
biogenic if made up of shell fragments. ▪ Evaporates or chemical precipitates: salts. Form from
water evaporation. Include limestones but also halite
(salts) and gypsum (CaSO4)
• Metamorphic: Formed at higher temperate and pressure in Earth’s
crust with no magma involved (no melting)
o Banded gneiss: Squeezed at high pressure and temperature
within the Earth’s interior (looks like how fudge is “layered” into
ice cream). Glacial ice is a good low temperature material
analogous to metamorphic rocks. The snowflakes are the
base but then as more builds up so does pressure then the
flakes change to more of a grain shape that becomes more
solid of a state (this change is metamorphism)
• Igneous, metamorphic, and sedimentary rocks form under distinct P
and T conditions
o Lithification and diagenesis= Cementation of sedimentary
o Low, medium, and high grades refer to relative conditions or
o Igneous processes require a high temperature, viscous liquid -
“melt” August 31, 2015
• Rocks: Composed of numerous grains of one or more minerals
cemented together or held together by interlocking texture
• Igneous: preserve textures formed at high T and P in presence of
melted crystallized (frozen) from a high T (700-1000 C) riscous melt,
over several hundred degrees, to a mix of solids.
o Volcanic: formed on surface, plutonic, formed with Earth
o Grain size depends on the rate of cooling (fine/glassy=fast,
o Gas (H2o, CO2, minor SO2,H2S) present as bubbles or
dissolved in melt
o Magmas: mix of melt, solids, and gas
• Sedimentary: Form at surface by accumulation of
o Clastic: formed by accumulation of sand, gravel, silt;
transported by wind, water, or ice; held together by cement
(CaCO3 or SiO2) precipitated by ground water; commonly
formed in layers
o Biochemical: mediated or created by organisms (peat, coal,
o Evaporate: chemical precipitates; commonly from seawater
(ex: salt, gypsum)
• Metamorphic: recrystallized at high P and T; no melting; preserve
metastable minerals (how did they get to surface?); banded or
• Low Tanalogue: Snow glacial ice
• Campus bedrock: Athens Gneiss
• Absolute key constraint for earth evolution
• Relative time: rock A is older than Rock B
• Absolute time via geochronology
o Are very needed
o Based on natural radiological activity
o Superposition: In a set of layers, the lowermost is the older.
Layers build up over time; superb exposure of layered
sedimentary rocks in Grand Canyon and other parks.
• Correlation of unique fossils between locations constrain time
o If you find the same kind of animal fossil in two different
locations you can assume that the layers are the same age.
Think of dinosaurs- they were only around for a short time and therefore, and layers with the fossils are the same age. By
building up the context we built a geological time scale.
o Correlations in US Southwest: Same age, age sequences
extended based on correlations.
o Why do layers of same age end up “tilted (at different heights)”
▪ Deposition of tilted layers as originally horizontal layers
▪ Tilting of layers
▪ Deposition of upper, horizontal layers
▪ Had to occur during the intercal between deposition of
the uppermost tilter layer, and the lowermost horizontal
• James Hutton, father of modern geology, Scotland. Spent years
trying to understand how the rocks on earth were made. Sicker Point
was the place that he discovered the earth was incredible old (the
church said that it was only 6,000 years old).
• Thought that the earth was formed from Meteorites colliding and the
entire earth was molten lava. Kelvin believed that the Earth is
cooling down and used thermodynamics to guestimate a new age
for the planet. Wrong, but held the keys to unlocking the true age of
• 1911, Arthur Holmes, used radiation to date how old the earth is.
Radio active uranium turns to lead. Collecting sample and data
allowed him to accurately date the earth. 4.5 Billion years (still today
the accepted time), Known as Deep Time
Glacial Lake Sediments
• One can count the dark and light layers (=1 year) and absolute
• The same thing can be done with snow layers in the polar ice caps
• Problem: record only goes back a few 100,000 years.
• Isotopes: same element but different numbers of neutrons, and thus
a different atomic mass; Uranium 238 vs. Uranium 235. Some
isotopes undergo spontaneous decay to a new element. Decay
involves ejection of particle from nucleus or capture of electron by
nucleus. Also change in number of protons and in some cases
• Radioactive Decay generates heat and is part of the reason why
Earths inner parts are hot and why we have volcanoes. • 4 radioactive elements present in significant amounts: U238, U235,
• Is analogous to an hour glass Sand empties from top to bottom- it
takes a fixed amount of time. Each decayed parent (Top) becomes
a daughter (bottom). It takes the same amount of time each time for
the sand to empty. This is the same for radioactive elements: they
each have a distinct half-life. Half-life is not changeable, each
element has a different half-life. Half-life= the time it takes for ½ the
parent atoms to decay to the daughter.
o Rule of thumb: after 7 half-lives, radioactive clock no longer
works- effectively no parent left.
▪ 14C has a half-life of 5,730 so why is it still around?
• It’s currently being generated. Cosmic rays from
the sun come into the top of our atmosphere and
mixes with 14N, which causes 14C and 1H to
• Our atmosphere is well mixed so the 14C is
evenly distrusted close to equal in the air.
• Living things have 14C in them while alive,
including humans. However, after death the 14C
begins to decay. It decays at a fixed rate and
time since death and can be calculated from
14C/14Co= e^-(Lambda)t where Lambda is the
decay constant for 14C; 14 Co is the standard
o K40 decays to Ar40
▪ K is 93% K39, .012 K40, and 6.7% K41
▪ Half-life is 1.25 billion years, which is helpful because
useful for a long period of time
▪ Daughter is a gas, Ar40
▪ Particularly used to measure argon (gas) because it
only accumulates after magma crystalized and cooled.
Therefore, the older the rock, the more Ar40 it has
• Therefore, No Ar40 has been gained or lost,
which means that no K40 has been gained or lost
(like the sand timer thing, you can’t take any sand
out, it’s all still there) = Closed system.
How old is the Earth?
• As you go to the coast of continents the age of rocks gets younger.
They grow outward • Where does the 4.55 Billion years of age come from?
o We look out to our nearest neighbor, the moon. So how old
are the oldest moon rocks? About 4.5 billion years, and are
from the highlands (aka the light colored areas od the moon)
o Another way is to look at meteorites. They peak in the
meteorite ages at 4.5 billion years. It’s not derived from the
materials on the Earth’s surface but rather from meteorites.
(and the moon backs this up)
• Model for the origin of solar system: all of the planets, moons, the
sun and asteroids formed at the same time from a dust cloud around
the “proto sun.” In some cases later events disturbed the
geochronology- so the oldest ages date the age of the solar system.
Thought that the Earth formed at the same time as the oldest rocks
in the solar system. September 2, 2015
• Time: Relative ages
o Lowest layer is the oldest
o Correlation: key fossils can indicate 2 rocks are the same age
o Cross cutting: igneous rocks that “intrude” (=cross cut) are
younger than host rocks.
• Siccar Point:
o Inclined layers tilted
o Incline layers deposited
o Vertical layers tilted
o Vertical layers deposited (oldes