Lab 1 - Dimensions and Structure of Planet Earth

Physical Geology Laboratory Manual Charles Merguerian and J Bret Bennington Geology Department Hofstra University © 2006 PHYSICAL GEOLOGY LABORATORY MANUAL Ninth Edition Professors Charles Merguerian and J Bret Bennington Geology Department Hofstra University i ACKNOWLEDGEMENTS We thank the entire Geology Department faculty and staff and all of our former Geology 001 students for pointing out errors in the text and for helping us develop and improve these laboratory exercises. We dedicate this manual to the memory of Professor John E. Sanders, whose inspiration and input are sorely missed. Physical Geology Laboratory Manual, Ninth Edition Copyright © 2006, 2005, 2004, 2003, 2002, 2001, 2000, 1999, 1998 by Charles Merguerian. All rights reserved. ii Table of Contents Lab Laboratory Topic Page 1 Dimensions and Structure of Planet Earth 1 2 Physical Properties of Minerals 27 3 Mineral Identification 41 4 Mineral Practicum 51 5 Rock Groups and Rock Properties 53 6 Rock Identification 69 Optional Exercise 6.1 – Plutonic and Extrusive Igneous Features 79 7 Rock Practicum 81 8 Introduction to Topographic Maps 83 9 Topographic Contour Maps, Profiles, and Gradients 101 10 Earthquake Location and Isoseismal Maps 115 A Future Earthquake in New York City 131 Appendix A: Geologic History of the New York Region 137 References 159 Mineral and Rock Practicum Test Forms 161 How to Get Help and Find Out More about Geology at Hofstra Email: All Geology professors can be contacted via Email: Full-time Faculty: Dr. J Bret Bennington (geojbb@hofstra.edu), Dr. Christa Farmer (geoecf@hofstra.edu), Dr. Charles Merguerian (geocmm@hofstra.edu), and Dr. Dennis Radcliffe (geodzr@hofstra.edu). Adjunct Faculty: Dr. Nehru Cherukupalli (geoncc@hofstra.edu), John J. Gibbons (geojjg@hofstra.edu), Dr. Lillian Hess Tanguay (geolht@hofstra.edu), Dr. Richard S. Liebling (georsl@hofstra.edu), Steven C. Okulewicz (geosco@hofstra.edu).. Internet: We encourage everyone to visit our internet site at: http://www.hofstra.edu/Academics/HCLAS/Geology Here you will find information and study materials relating to this and all other geology classes offered at Hofstra. Individual faculty websites are helpful as well. Geology Club: If you are interested in doing more exploring on field trips and in learning more about geology and the environment outside of class, we invite you to join the Geology Club! Meetings are held every other Wednesday during common hour in 162 Gittleson Hall. Current events and upcoming trips are listed on our webpage. Geology Department: Pay us a visit! We are located on the first floor of Gittleson Hall, Room 156 (Geology Office, 463-5564). The secretary is available from 9:00 a.m. to 2:00 p.m. to answer questions and schedule appointments but the department facilities are available all day long. Free tutoring is available throughout the semester and lab materials (mineral and rock specimens, testing equipment, maps) are available for additional study in 135 Gittleson. iii iv Lab 1 - Dimensions and Structure of Planet Earth PURPOSE Our first lab is intended to show you how some very basic characteristics of the Earth such as its shape, volume, internal structure, and composition can be discovered using relatively simple observations and measurements (no need for satellites, lasers, and other high-tech tools.) In the first part of this exercise, you will read about how the size and shape of the Earth can be demonstrated from observations made at its surface. You will read an account of how a pioneering genius of mathematical geography, Eratosthenes of Alexandria, put together some significant geometric data in ancient Egypt and used them to calculate the circumference of Planet Earth. Because the Earth approximates the shape of a sphere (in truth it is an “oblate spheroid” - a sphere with a bulging waist), knowing its circumference allows you to calculate its radius and volume. In the second part of this lab, you will “weigh the Earth” (estimate its mass) by making some measurements with a simple pendulum. Knowing the Earth’s volume and mass allows you to calculate its density. Finally, you will weigh some specimens of minerals and rocks — samples of typical Earth-surface materials — in air and in water and use these weights to compute the densities of these materials. By comparing the density of the entire Earth to the densities of common surface materials you will be able to draw some useful conclusions about the structure and composition of the Earth’s interior. PART I: THE SHAPE AND SIZE OF THE EARTH As a resident of the Earth during the Space Age, you may never have experienced any difficulty accepting the idea that the shape of the Earth closely approximates that of a sphere. Televised images of the Earth taken from the Moon (Figure 1.1), for example, have convinced nearly everyone of the correctness of this concept of the Earth's shape. (There is, however, a small minority of people who still maintain that the Earth is flat and others who insist that the Moon landings were faked as part of an elaborate hoax perpetrated by NASA.) Many people take it for granted that Christopher Columbus discovered that the Earth was round, but in truth, the fact that the Earth is a sphere was accepted by natural philosophers two thousand years before Columbus set sail. Evidence From Early Astronomical Observations The famous Greek mathematician Pythagoras (6th century B.C.) noted in about 520 B.C. that the phases of the Earth's Moon (Figure 1.2) are best explained by the effect of directional light on the surface of a sphere. Therefore, he reasoned, if the Moon is a sphere, so too, is the Earth likely to be spherical. In 350 B.C., another famous Greek, Aristotle, argued that the shape of the Earth's shadow across the Moon at the beginning of an eclipse is an arc of a circle (Figure 1.3). Only a sphere casts a circular shadow in all positions. 1 Figure 1.1 - The Earth viewed in December 1968 from a lunar-orbiting spacecraft at a distance of 160,000 km. The curved surface at bottom is the surface of the Moon. (NASA.) Figure 1.2 - The Lunar Phases (from top left to bottom right: waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning cresent) 2 Figure 1.3 - Total lunar eclipse of Wed 09 December 1992 photographed from Jones Beach, NY with the shutter of the camera opened at intervals from 1700 h to 1810 h without advancing the film. (Bill Davis, Long Island Newsday.) Ancient astronomers found only one star in the heavens that did not change position in the sky throughout the year: the pole star. They named the star directly above the Earth's North Pole, Polaris. Figure 1.4 shows the results of a modern time exposure: a picture taken from a camera with its shutter kept open for many hours mounted on a telescope and pointed into the nighttime sky at the star Polaris. As the Earth rotates, the stars appear to move in circles across the sky. Notice that moving towards a point in the sky directly above the North Pole the circles become smaller and smaller. The tightest circle is made by Polaris (alas, Polaris is no longer directly above the North Pole - if it were it would appear as a single dot, the only apparently ‘fixed’ star in the picture.) Even without cameras, by observing the motions of the stars, ancient astronomers found that they could identify in the sky the position directly above the Earth's pole of rotation and could use this as a fixed point of reference. Once they had established such a reference, the ancient astronomers could then define a plane perpendicular to this line. The plane perpendicular to the Earth's pole is named the Earth's Equator (Figure 1.5). Once they could identify the pole star, astute ancient observers noticed that when they traveled from north to south, the position of the pole star in the nighttime sky changed. In Greece, for example, they saw that the pole star is higher in the sky than it is in Egypt. If the Earth's surface were flat, then at all points on the Earth the elevation of the pole star should be the same. A change in elevation of the pole star as a function of location on the surface of the Earth could be explained only if the shape of the Earth were spherical (Figure 1.6). This kind of 3 observation enabled the ancient Greek geographers to define latitudes - lines on the surface of the Earth made by circles parallel to the Equator (Figure 1.7). Other experiences relating to the shape of the Earth involved the observations of sailors, who saw ships disappear below the horizon, or found that their first views as they approached land were of the tops of hills. The shorelines appeared only after their ships had approached close to land. Figure 1.4 - The Earth turns on its axis as shown by this 8-hour exposure with a fixed camera pointed at the North Pole. The heavy trail near the center was made by Polaris, the North star. (Photograph by Fred Chappell, Lick Observatory.) 4 Axis Equator Figure 1.5 - Earth's Equator defined as a plane perpendicular to the polar axis of rotation. ve ve th abo the ob y abo e ob y se Sk se Sk rver rver is r la ris o a P ol P m s o i m r x ro f a t f t h h 's g g Straight up Straight i up Straight L i th L r a Horizon is Horizon E ax 's rth Ea 75 Þ N E qu at E or q u 4 a 5 to Þ r N Figure 1.6 - Changing height of Polaris (the pole star) above the horizon as seen by observers at two different latitudes on the surface of the Earth.

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