Download Geology 001 Exam 1 Review – Planet Earth Updated 10/12 Review

Geology 001 Exam 1 Review – Planet Earth
Review all questions discussed in class (see presentation pdfs for review)
Updated 10/12
Earth Systems:
Hydrosphere – water vapor, salt water, fresh water, ice. 97% of water is saltwater. Most
freshwater is found as ice. Largest reservoir of liquid water is groundwater.
Atmosphere – composition of Earth’s atmosphere – Nitrogen, oxygen, greenhouse gases (water
vapor, carbon dioxide, methane). Most gas is located near to the surface in the troposphere.
Greenhouse effect – greenhouse gases trap heat radiated from the surface, prevents heat from
escaping into space, keeping the Earth habitable.
Ozone layer – located in the stratosphere, absorbs deadly UV radiation from the Sun.
Biosphere – life – interacts and affects other systems (examples are provided in the lecture notes)
Geosphere – Earth has distinct continents and oceans basins, extensive mountain systems, lack of
craters, active volcanoes and earthquakes – active planet inside and out, surface constantly being
remade by uplift and erosion.
Solar System: Sun, rocky planets (Mercury, Venus, Earth, Mars), gas giants (Jupiter, Saturn), ice
giants (Uranus, Neptune), minor planets (plutinos, asteroids), comets
Origin of Elements
Elements are made of atoms. The number of protons in an atom determines what element it is.
Hydrogen (a single proton and electron – the simplest and most abundant element) and helium
were created in the Big Bang at the origin of the universe (Big Bang nucleosynthesis). Heavier
elements (lithium – iron) are made by nuclear fusion in the interior of stars (stellar
nucleosynthesis). Most stellar nucleosynthesis occurs via the fusion of helium nuclei, so that
elements with masses that are multiples of four (e.g. carbon, oxygen, silicon) are the most
abundant. The heaviest elements (atomic mass > iron) are produced by neutron bombardment of
iron and other elements when massive stars explode in a supernova.
Planets and stars form from the collapse of interstellar clouds of dust and gas and incorporate the
debris (mix of elements) created by previous generations of stars.
Earth formed from refractory materials that were able to condense to solid form at high
temperatures in the inner solar system. These materials were rich in iron, and oxides of silicon,
iron, and magnesium. Early in the history of the Earth the planet melted and the metallic iron
collected in the center to form a core, separating from the rocky material that formed a mantle.
The lightest rocky compounds rose to the surface to form a crust. The origin of the volatile
materials such as water, carbon dioxide, and nitrogen that make up the Earth is uncertain. Most
of these materials could have been added to the Earth after it formed by impacts from icy
asteroids and comets.
Minerals
Elements are the building blocks of minerals. Minerals combine to form rocks. Silicon and
oxygen are the most abundant mineral-forming elements.
Definition of a mineral (solid, crystalline, naturally occurring, distinct elemental composition,
not organic C-H molecules)
Mineral properties (luster, hardness, cleavage, streak, etc.)
Relation of mineral properties to crystal structure (diamond vs. graphite)
Renewable, non-renewable, and recyclable resources (can you provide examples?)
Ore – a rock containing a useful element in quantities that can be mined economically.
Mineral families: Silicate minerals (silicate tetrahedron) – four atomic bonding sites allows
complex structures such as chains, sheets, and 3-D frameworks. Silicates are the major rockforming minerals and are valuable in bulk as construction materials (sand, gravel, crushed rock,
building stone, glass).
Other minerals families and their uses: Carbonates (calcite – cement, also a rock-forming
minertal), Phosphates (apatite – bones, teeth, useful as fertilizer), Sulfates (gypsum – plaster),
Halides (halite – salt), Oxides and Sulfides (simple compounds – ore minerals), Native elements
(gold, platinum)
Earth’s Interior Structure and Function:
The Earth is heterogeneous and layered – density of the whole planet = 6 gm/cc, density of the
crust = 3 gm/cc, layer boundaries come from monitoring seismic waves as they travel through
the Earth. P waves show boundary layers as discontinuities at depths in the Earth where the P
waves suddenly increase in velocity. P waves show the Earth to have a crust, mantle, outer core,
and inner core. S wave shadow zone indicates that the outer core is liquid because P waves can
pass through it but S waves cannot. Decrease in P wave velocity also shows a weak zone in the
upper mantle (the asthenosphere).
Source of Earth’s internal heat – nuclear fission due to radioactive decay of heavy elements.
Source of Earth’s exterior heat that drives circulation in the atmosphere – the Sun.
Layered structure of the Earth: Inner Core (solid), Outer Core (liquid), Mantle (solid),
Asthenosphere (plastic), Lithosphere (upper Mantle + Crust, solid)
Pressure and temperature both increase from the surface to the core of the Earth
Pressure raises the temperature needed to melt a particular material.
Phenomena arising from the layered structure and composition of the Earth:
Planetary magnetic field – generated by a magnetic dynamo set up by the circulation of the iron
in the liquid outer core around the solid inner core. The magnetic field shields the Earth from the
high energy charged particles of the solar wind, preventing our atmosphere from being eroded
away into space and also preventing life on the surface from being exposed to higher levels of
radiation from space.
Plate tectonics – lithosphere and asthenosphere. Lithosphere is the plates composed of crust and
upper mantle that “floats” on the asthenosphere. Ocean floor crust is mafic (enriched in iron and
magnesium) relative to continental crust (sialic – enriched in silicon and aluminum).
Earth’s mantle behaves like a lava lamp, circulating very slowing to deliver heat to the upper
mantle where plumes of hot mantle are rising. Where heat is rising, magma erupts to form shield
volcanoes at hot spots. Where plates are separating, the asthenosphere wells up between the
plates and melts due to decompression forming new ocean floor lithosphere at mid-ocean ridges
(diverging plate boundary). Older lithosphere moves away from the ridge and eventually sinks
back into the mantle at ocean trenches (converging plate boundary).
Volcanoes at diverging plate boundaries and hot spots erupt hot, fluid lava to form shield
volcanoes. At converging boundaries volcanoes erupt explosively with gassy, sticky magma.
At converging plate boundaries, water is pulled down into the mantle with the old ocean floor
lithosphere. Mixing water with the rock in the upper mantle causes the rock to partially melt at a
lower temperature, releasing cool, viscous, gas-rich magma (flux melting). This magma is also
silica rich and forms continental rock when it cools near the surface of the Earth.
The Earth has continents because of this plate tectonic process, which has been making
continental rock and adding it to the lithosphere for most of the history of the Earth.
Important questions to be able to answer:
Why does the Earth have so few impact craters relative to other planets such as the Moon and
Mars?
Why is the surface of the Earth segregated into continents (elevated regions) and ocean basins
(depressed regions)?
What are some examples of interactions between Earth systems? For example, how does the
biosphere change the atmosphere?
Why did Carl Sagan (famous astronomer) mean when he said that “We are all made of star
stuff.”?
Why are iron and silicate minerals the materials that make up the bulk of the Earth?
Why do graphite and diamond have such different physical properties even though they are both
made out of pure carbon?
Is water a mineral? Why or why not, and under what conditions?
Why are most minerals in the crust of the Earth silicate minerals? What makes silicate minerals
so abundant and diverse?
Why are fossil fuels considered non-renewable resources? What about iron? Should we be
worried about running out of iron? Why or why not?
If fresh water is a renewable resource, how is it that it is often scarce? What does it mean to use a
resource like water sustainably?
How can a body of rock that is currently not considered an ore become an ore later?
Why are most metal ores in the oxide and sulfide mineral families?
What causes some layers in the Earth to be solid, others are liquid or plastic?
Earth’s magnetic field – how is it generated? Why is it important? What is an aurora?
What will happen to the core of the Earth as the Earth continues to cool inside? How will this
impact the Earth’s magnetic field?
Mars has very little atmosphere and no current magnetic field (however, magnetized rocks in the
crust suggests that in the distant past, Mars had a very strong magnetic field). Yet there is
evidence for Mars having been a warmer, wetter world early in the history of the solar system.
What happened to Mars? How might Mars have gone from being a warm, wet world to being a
dry, cold world early in its history?
What causes volcanoes at divergent plate boundaries? What causes volcanoes at convergent
plate boundaries? What happens when water is added to rock in the mantle? How does the
recycling of the Earth’s lithosphere create continental crust? Why don’t Mars and Venus have
true continents like the Earth does?