Midterm Exam #2 Study guide

Be prepared to define, describe, and differentiate
- plate tectonics, subduction, the earth's, mantle, sea floor spreading
- the short and long term organic carbon cycle
- the inorganic carbon cycle
- the carbonate-silicate cycle
- photosynthesis, respiration and decay, fossil fuels
- K-T extinction
- glacial / interglacial
- the 'Younger Dryas' (and where the name comes from); the Holocene
- Medieval Warm Period;  Little Ice Age
- "snowball earth"
- cycles in precession, tilt, ellipticity of the earth's orbit
- sunspot cycle

Be prepared to
- list and briefly describe the more important external influences on the earth's climate over its 4.6 billion year history and for each one, know roughly the range of time scales on which it operates.
- list and describe some of the kinds of evidence that is used to infer what past climates were like.
- summarize what ice cores and sediment cores ice cores tell us about the history of the ice ages.
- summarize the major elements of the Milankovitch theory of the ice ages
- list the major carbon reservoirs in the Earth system and contrast their relative sizes and residence times.
- define and describe the role of processes such as photosynthesis, weathering, limestone formation, and the burning of fossil fuels in moving carbon between the major reservoirs.
-describe the oceanic biological pump and how it operates.
-contrast the composition of the earth's early (pre-life) atmosphere with the present composition of the atmosphere.

Be able to answer the following questions, citing observational evidence as appropriate:  How do we know that
- life on Earth dates back almost 4 billion years?
- oxygen levels in the atmosphere started rising roughly 2 billion years ago?
- the earth was relatively warm during the Mesozoic period (250-50 million years ago)?
- the continents are drifting?
- the Atlantic Ocean is widening?
- a series of major ice ages (the so called Pleistocene epoch) began 1-2 million years ago?
- global sea level was more than 100 meters lower during the peak of the last ice age than it is today?
- carbon dioxide levels in the atmosphere were ~30% lower during the major glaciations of the last million years than during interglacials?

Why do scientists believe that
- the temperature of the Earth has always remained well below 100 C?
- there were periods in the earth's history when it was fully glaciated?
- complete glaciation of the earth would likely be followed by an interval of extreme warmth?
- carbon dioxide levels in the atmosphere have decreased over the lifetime of the Earth?
- oxygen levels in the atmosphere have remained between 13 and 35% during the past 360 million years?
- the burning of fossil fuels does not pose a serious threat in terms
of the loss of atmospheric oxygen?
- the climate system is capable of undergoing sudden climatic changes?
- the melting of Arctic sea ice wouldn't impact global sea level asmuch as the melting of an equivalent amount of ice from the Greenland ice sheet?
- the upper limit that atmospheric carbon dioxide concentrations could reach as a consequence of the burning of fossil fuels is roughly a factor of 6 relative to present concentrations?
- Mars and Venus don't have ozone layers like the earth does?
- continental drift was not an important factor in accounting for the ups and downs in global temperature during the past million years?
 

Some sample questions and answers:

Q.  Where does most of the carbon reside in the Earth system?
A.  Most of carbon is in the form of limestone in sedimentary rocks.

Q.  Describe the role of weathering in the carbonate-silicate cycle. What kind of chemical transformation is involved?  What happens to the products of the reaction?
A. Weathering decomposes calcium silicate rocks formed within the earth's crust into silicon dioxide (quartz) rocks and calcium ions.
The calcium ions are carried by rivers into the sea where they are eventually incorporated into calcium carbonate (limestone) sediments
through the action of marine organisms.  The quartz minerals are eventually subducted into the magma below the earth's crust, where
they react with limestone to form calcium silicate rocks again.

Q.  For each of the following kinds of proxy evidence, indicate the time scale on which it provides useful information on past climate variability.
(a) tree rings,
(b) 'redbeds' containing ferrous oxide
(c) ice cores
(d) magnetic stripes,
(e) fossils.  In answering the
question use the categories A lifetime of the earth, B the past 100
million years, C the past million years, D the past 20,000 years, and
E the past 2000 years.  Note that some kinds of proxy evidence
provide useful information on more than one time scale.

A. (a) tree rings  E, (b) redbeds A, (c) ice cores CDE, (d) magnetic
stripes B, (e) fossils ABCDE.