The "Reading Questions" below refer to portions of the two articles above (provided in class). Respond to each of these questions by highlighting the passage(s) in the corresponding article that address(es) the question and labeling it with the number of the question. (Circle the number label to make it easily visible.) We will have a round-table discussion
of the topic of these articles in class on the due date above and continued at the following class meeting. (Completing this assignment in advance should
help prepare you to participate. Your response to the reading questions is worth 10 pts. Your participation in the discussion is worth 5 pts. [The points establish the value of the item relative to other items in the portion of the class devoted to reading, discussing, and writing about articles from the literature.])
"The Earth's Orbit and the Ice Ages"
How did the earth's climate 18,000 years ago differ from today's climate?
What is the main assertion of the Milankovitch theory?
What data are used to estimate the global volume of ice? What are the two advantages of these data?
Why is the Milankovitch theory more attractive than alternative hypotheses as an explanation for the
Pleistocene ice ages?
What three parameters characterize Earth's orbit around the sun?
What
can cause these parameters to change? How much has each parameter
changed over the last several hundred thousand years, and how rapidly has
each changed?
What effect do changes in obliquity (tilt) have? What effect does precession of the Earth's axis of rotation have, combined with precession of the orbital ellipse around the sun? What effect do changes in orbital eccentricity have? Which of these changes in orbital parameters causes changes in the annual, global average insolation, and how large a planetary temperature change would this by itself produce?
According to the Milankovitch theory, how can small changes in total insolation,
and the redistribution of solar radiation over the course of the year, produce
ice ages? What is the key to understanding how this can happen? Why is the
Northern Hemisphere the most important, according to this hypothesis?
When did evidence sufficient to convince most skeptics finally accumulate? What kinds of evidence did the trick?
Why was the accumulation of relatively recent geologic evidence still not
sufficient to close the case in favor of Milankovitch theory, from the perspective
of scientific argument? How was that shortcoming addressed?
What are some possible explanations for why the 100,000
year cycle of variation in orbital eccentricity is so prominent in the
climate record, given how small
the perturbation it produces in insolation compared to that produced by precession and variations in obliquity?
What features of the Pleistocene climate record can the Milankovitch theory
not explain?
"Unlocking the Mysteries of the Ice Ages"
Hays et al. (1976) found δ18O variations in marine sediments at periods of 41,000 and around 21,000 years, which they expected, but they also found strong variations at 100,000 years, which they didn't expect. Why wouldn't they have expected 100,000 year cycles under Milankovitch theory?
How does the period and pattern of development of individual glacial cycles of the late Pleistocene (the last 1 million years) compare to those of the early Pleistocene and late Pliocene (1-3 million years ago)?
Why is the lack of observational evidence for 19,000 and 23,000 year cycles during
the early Pleistocene and late Pliocene surprising?
This paper summarizes two hypotheses,
one by Peter Huybers and one by Maureen Raymo, for why 41,000 year (nutation) cycles dominate the paleoclimatic evidence in the early Pleistocene and late Pliocene, whereas evidence for the 19,000 and 23,000 year (precession) cycles is lacking. What were their hypotheses?