EARTH / ISP 350 -- PHYSICS OF THE EARTH
Fall Quarter, 2015
Instructor
Emile A. OKAL F-492 TECH, [+1-VIP-49] 1-3194
emile@earth.northwestern.edu
T.A.
Michael Witek
http://www.earth.northwestern.edu/people/emile
Rm. F-481, TECH, [46]7-7819
mwitek@earth.northwestern.edu
Class meets M, We, F at 1:00 p.m.; discussion session Th. at 1:00 p.m., I.S.P. HOUSE
Additional lecture Tu at 11:00 a.m., TECH F-280
NOTE: Discussion section may be moved inside a given week
Topics Covered and Tentative Dates
1.
BASIC FACTS about the Earth: MON 21 SEP
Overview of Plate Tectonics (the ‘‘New View’’ of the Earth): THU, 24 SEP
(in care of T.A. during "discussion" session at 1 p.m.)
2.
GRAVITY: Motion of planets, Shape of the Earth, Tides. Gravity Anomalies, Isostasy:
TUE 22 SEP to MON 28 SEP.
3.
SEISMOLOGY: Continuum Mechanics, Wave Equations, Body and Surface Waves:
TUE 29 SEP to FRI 09 OCT.
Internal structure of the Earth; composition of the Earth:
Earthquakes: location and focal mechanisms:
4.
MON 19 OCT to MON 26 OCT.
GEOTHERMICS: Temperatures in the Earth. Conduction and convection mechanisms:
Lateral heterogeneity in the Earth: TUE 27 OCT to WED 04 NOV.
<<<
5.
MON 12 OCT to FRI 16 OCT.
MID-TERM: FRIDAY 30 OCT 2015 >>>
GEOMAGNETISM and PLATE TECTONICS: Earth’s magnetic field. Paleomagnetism;
marine magnetic anomalies; Kinematic models of Plate Tectonics; Elementary Dynamic
models: FRI 06 NOV to THU 12 NOV.
-26.
RADIOACTIVITY: Principles and absolute dating methods; age of the Earth. Chemical
differentiation of the Planet: FRI 13 NOV to FRI 20 NOV.
7.
SELECTED TOPICS in the SOLAR SYSTEM: A detailed look at topics selected from
ongoing research, an extension of the material covered to other planets in the solar system,
and an overview of the latter’s history in the past 4.6 billion years. MON 23 NOV to WED
25 NOV.
FINAL EXAM
THURSDAY 10 DECEMBER 2015, 09:00 to 11:00 a.m.
• Note that problem sets are due ON TIME, and will not be accepted late except in documented
emergency or with prior consent of T.A. and/or instructor.
•
EAO does not keep formal ‘‘office hours’’, but rather welcomes students any time.
I am usually around the Geology Department from 8:00 a.m. (occasionally earlier) to 8:30 p.m.,
occasionally much later; also more than I would like to think during week-ends. Walk in any time
the door to F-492 TECH is open (note that there is an inner office in which I may be concealed
from direct view; students have missed me in the past). When not in his office, EAO often hangs
out in the Lab next door (F-491), or in the Seismological Archive Facility in Seabury Hall
([46]7−2619).
You are welcome any time I am present, except when teaching my other class (EARTH 103 –
TuTh 12:30) and during Friday afternoon Departmental Seminar (3:00 to 4:00 p.m.; to which you
are also, of course, welcome).
Messages can be left with the Geology Department Secretaries ([+1-VIP-49]1-3238), FAXed to
[49]1-8060, or sent by electronic mail to EAO or T.A.
Book and Notes
This book is not required; but is recommended as a reference to the class; in other words as
"another version of the Gospel..."
W. Lowrie: Fundamentals of Geophysics, Cambridge University Press 2nd Edition,
ISBN-13 978-0-521-67596-3
Class Notes will be handed out regularly, and will eventually constitute a 200+ page volume. The
notes will be regularly deposited on a class website at
www.earth.northwestern.edu/people/emile/350.Fall15
Additional reading may be taken from various texts which will be put on reserve.
Class Grade will be an average of Problem Sets (25%), Midterm (25%), and Final (50%).
Special projects for extra credit (involving substantial analytical or computer calculations) may
become available and will be announced in due time.
-3Units used by Earth Scientists
Only metric units are permitted in this class (SI or cgs). ‘‘British’’ units, such as inches,
furlongs, tablespoons, ounces (both troy and avoir-du-poids), BTUs, or °F are prohibited.
However, the following units are widely used in the Earth sciences and will be used extensively in this class:
Length:
One Earth radius a = 6371 km
One ‘‘degree’’ (°): the length of Earth circumference subtended by a 1°-angle at the
Earth’s center 1° = π a/180 ≈ 111. 20 km
One nautical mile (nau. mi.) = 1°/60 ≈ 1.853 km
Time:
One year (yr or ‘‘a’’, for Latin ‘‘annum’’) ≈ 3. 15 × 107 s
One million years (Ma); one billion years (Ga), occasionally (incorrectly) written as
m.y. or b.y.
Note that the correct symbol for ‘‘second’’ is s, not sec.
Mass:
No special unit; mass of Earth is 6 × 1024 kg
Note that the correct symbol for ‘‘gram’’ is g, not gm.
Pressure: One bar = 106 baryes (or dyn/cm2 ; cgs) = 105 Pa (Pascal or N/m2 ; SI). This unit is
convenient since the average atmospheric pressure at sea level is 1.013 bar.
Kilobars (kbar) and Megabars (Mbar) are widely used; 1 bar = 100 kPa; 1 kbar =
100 MPa; 1 Mbar = 100 GPa.
Velocity:
Seismic waves measured mostly in km/s = 103 m/s.
Plate motions measured mostly in cm/yr = 3. 3 × 10−10 m/s.
Note problems arising from such formulæ as
µ = ρα 2 , where ρ = 3 g/cm3 ;
α = 6 km/s.
Result (108) is in GPa or tens of kbar !
Energy:
The calorie (1 cal = 4.182 J) is still used. As a result, heat flow is occasionally measured in µcal/(cm2 s) called Heat Flow Unit (HFU); 1 HFU = 42 mW/m2 . This unit is convenient,
because it is close to the average flux of heat escaping the planet from the oceanic floor.
IMPORTANT
Note that it is incorrect to give an answer for a numerical result with more significant digits than
given in the question. For example, such answers as ‘‘4.5578264702342 Ga’’ for the age of the
Earth are WRONG if computed from a radioactive life-time given with only three significant digits. The correct answer is ‘‘4.56 Ga’’ or ‘‘1. 44 × 1017 s’’. Repeat offenders of this point of scientific common sense† will LOSE points from grades; you have been warned.
† If you are not convinced, note that the last digit (2) in the example above corresponds to 50 mn.
Do you really want to measure the age of the Earth to a precision of 50 minutes?
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