Geology 001 Exam 2 Review Spring 2013 – Rock Cycle and Isostasy, Carbon Cycle, and
Climate Change
Review all questions discussed in class (see presentation pdfs for review)
Rock Cycle:
Three main origins of magma: eruption of mantle magma at hot spots and mid-ocean ridges to form dense, silica-poor rock of the seafloor (basalt, gabbro), eruption of silica-enriched magma formed at subduction zones from the melting of the upper mantle mixed with water – forms continental rock (andesite, diorite), magma derived from remelted continental rock to form very light, silica-rich continental rock (rhyolite, granite).
Weathering of igneous rock to sediments and ions – mechanical weathering and chemical weathering. Breakdown of silicate minerals such as feldspar into clay and bicarbonate ions by reaction with carbonic acid in rainwater.
Formation of sedimentary rock by deposition. Main types of sedimentary rock: detrital
(conglomerate, sandstone, mudstone), carbonate (limestone, dolostone), evaporite (rock salt, rock gypsum), and organic (coal). Fossils are preserved in sedimentary rock. Fossil fuels derive from organic material trapped in sedimentary rock - plants = coal, algae = tar, oil, natural gas
Burial of sedimentary rock to form metamorphic rock. Foliated metamorphic rock (slate, phylite, schist, gneiss) vs. nonfoliated metamorphic rock (marble, quartzite). Progressive metamorphism with increasing pressure and temperature - 3 Rs: regrowth, recrystallization, reorientation. Metamorphism converts minerals that are stable at surface temperature and pressure to new minerals that are stable at high T and P.
Paths through the rock cycle: uplift of metamorphic rock, weathering and erosion, deposition of sedimentary rock. Other paths through the rock cycle (e.g. melting of metamorphic rock to make magma and igneous rock.)
Mechanisms of uplift and subsidence – related to isostasy (lithosphere floating in balance on the asthenosphere) – changes in density of the crust (heating / cooling), changes in thickness of the crust (plate collisions – thicken crust, erosion – thins crust). Erosion of mountain range from above causes rebound of rock in deep roots back toward the surface.
Earth’s Climate
Greenhouse Effect
Water, CO
2
, and methane are gases that are transparent to visible light but absorb infrared radiation. Sunlight passes through the transparent atmosphere and heats the surface of the Earth.
Heat (infrared energy) that is radiated by the surface of the Earth would escape back into space if not for the presence of greenhouse gases. These gases absorb escaping heat and warm the atmosphere and surface. The more greenhouse gases there are, the more heat is retained and the warmer the climate of the Earth is.
Carbon Cycle

Carbon in various Earth systems reservoirs – CO
2
in atmosphere, organic carbon in animals, plants, soils, fossil fuels, bicarbonate ion in oceans, carbonate rock in the lithosphere.
Organic carbon cycle - exchange of carbon from atmosphere to organic matter via photosynthesis and exchange of carbon from organics to atmosphere via oxidation and methanogenesis (methane production by bacteria).
Imbalance of exchanges due to burning of fossil carbon (coal, oil, natural gas) and changes in land use (deforestation) – fossil carbon removed from the atmosphere and stored in biomass, soil, and fossil hydrocarbon over hundreds of millions of years is being returned to the atmosphere by human activities in less than 200 years.
Inorganic carbon cycle – long-term storage of carbon in the lithosphere.
CO
2
in the atmosphere dissolves in the oceans as bicarbonate ion (solubility pump). Chemical weathering removes CO
2
by reacting carbonic acid with minerals to produce bicarbonate ion.
In the oceans, bicarbonate ion reacts with calcium ion to produce limestone, which stores carbon in rock form. If limestone is metamorphosed deep in the Earth CO mantle. Volcanic eruptions release CO
2
2
is released into the
back into the atmosphere, completing the cycle.
Inorganic cycle is a negative feedback loop – tends to maintain the level of CO
2
in the atmosphere needed to keep climate away from extremes of hot and cold.
Global Warming
Evidence for rising levels of CO
2
in the atmosphere: pre-1959 – samples of air from ice cores drilled in Antarctica and Greenland. Post 1959 – direct measurement of atmosphere (e.g. station on top of Mona Loa).
CO
2
is a greenhouse gas – traps heat radiated from the surface of the Earth, preventing it from being lost to space.
Current CO
2
levels double highest level of past 400,000 years.
CO
2
is correlated with global temperature for the past 400,000 years.
Uptake of 30% of human-produced CO
2
is acidifying the oceans (dissolved in water, CO converted to carbonic acid).
2
is
Evidence that the global climate is warming due to CO
2
:
Temperature records show increasing average global temp.
Climate zones are shifting north – growing seasons are changing.
Weather patterns and precipitation patterns are changing.
Lower atmosphere (troposphere) is heating up while the upper atmosphere (stratosphere) is cooling.
Computer models show close fit between predicted and actual change in temperature when CO
2
is incorporated as a greenhouse gas.
Some evidence for increasing intensity of hurricanes and other storm events.
Observation that glaciers, ice shelves, and sea ice are melting at unprecedented rates.
Why global warming and climate change is a problem:
Change is expensive to deal with – infrastructure is based on past conditions.
Agricultural regions and fisheries depend on climate remaining stable.

Melting ice causes rising sea level – coastal flooding.
More extreme weather and storms – droughts and floods.
Poor nations and poor people at greater risk.
Adapting to climate change will be very costly.
Ways to prevent or moderate CO
2
emissions and associated climate change:
Increase efficiency of energy use – less waste = less fuel burned.
Switch to non-carbon-producing energy sources – solar, wind, nuclear, geothermal.
Carbon sequestration – bury CO
2
emissions from fossil fuels.
Carbon tax – put a tax on CO
2
emissions to create an incentive to reduce them.
Cap and Trade – put a limit on CO
2
emissions and allow companies to sell unused emissions credits at a profit.
Carbon offsets – do something (e.g. plant trees) to uptake CO
2
to balance CO burning of fuels.
2
emitted by
Ways that YOU can reduce your personal carbon emissions? (Think about it!)