Joseph N. Frederick III
PSC 1121C
Spring 2011
Geophysics
Geophysics can be broken down into several groups that deal with physical science and the earth. It is a field and profession that combines geology, mathematics, and physics all in an effort for people across the world to understand the ways of the world and exactly what it takes for certain seemingly unnatural events to happen. Geophysics covers a range of ideas from gravity, heat flow, seismic waves that cause vibrations through the Earth’s layers, radioactivity both geothermal and geochronological, electricity, electromagnetic waves and magnetism, fluid dynamics, and even condensed matter physics. So as we see, geophysics is indeed a very broad subject, yet when looked at under specific lights, we see that geophysics is no more than a name, a container, for all matters Earthly related. Most of these topics will most definitely be covered in this essay and if not talked about in depth, definitely mentioned seeing as how all of these ideas are valuable to everyone worldwide in getting to know and understand the way our home planet works in relation to ourselves and the space we occupy in the universe. (Beroza, Nelson, and Ilich, "The Department of Geophysics").
History
The first traces of anything geophysically related first appear in regions inside of China during the Qin dynasty somewhere between two hundred twenty-one and two hundred six B.C. when Chinese fortunetellers used lodestones to create their fortune telling boards. Little did the Chinese know, the lodestones were actually natural stones composed of ferrites, also known as magnetic oxides, that attract traces of iron and other metals in the soil. Fortunately enough, because of this attraction, mixed with the natural magnetism of the Earth, when a lodestone was fashioned in the shape or form of a rod, it would align itself north and south. It wasn’t until this discovery was made that the Chinese saw that lodestones were not to be used simply for fortune telling but also to point out true directions relative to a persons positioning on the earth’s surface. Engineers quickly made plans to design the first ever compass, complete with the now traditional cardinal markings, the already discovered constellations, and a needle that would inevitably always point south. It isn’t until after more than one thousand years later, somewhere around the eight century between eight hundred fifty and one thousand fifty A.D. that we actually see the emergence of magnetized needles. Still based in China, we see the compass becoming very common as a proper navigational apparatus being used on sea faring vessels. Zheng He, an experienced navigator from the Yunnan province in China, was the first recorded individual to use the compass for navigational assistance during his seven ocean voyages between the years of 1405 and 1433. (Bellis, “History of the Compass”). Another exceptionally influential addition to the world of geology and geophysics was the discovery of the seismoscope. It’s original designer and architect is somewhat under dispute but research shows that Chang Heng was indeed the first creator of the world’s first seismoscope in 132 A.D. A seismoscope is a device that measures motions of the ground including seismic waves generated by earthquakes, volcanic eruptions, and other seismic causes. To this day the inner workings of Chang Heng’s seismoscope are still unknown, but from proper historical documentation we see exactly what it resembled on the outside. On a six foot diameter wine jar or similar vessel were eight dragon heads facing the respective eight directions we learn and see in the modern day compass, north, south, east, west, north east, north west, south east, and south west. Inside the open mouths of the dragons were a ball made of unknown material, most likely iron. Directly below each of these dragons was a respective toad facing toward their dragon. In the event of an earthquake, the ball inside the dragon’s mouth facing the origin of the seismic activity would fall into the open mouth of the toad. In one instance it was reported that an underground eruption was detected four hundred miles away with no vibrations being felt by inhabitants at the location of the seismoscope. It was innovations like these that paved the way and laid the groundwork for the ever so close, modern beginnings of the geophysics that scientists have come to know, love, and research today. (Bellis, “The Earliest Seismograph”).
Modern Beginnings Progressing into the seventeenth century we meet William Gilbert, a renowned doctor and physician in London, England in the time of Elizabeth I, and author and publisher of a book in 1600, three years before his death, called De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure also know as On the Magnet and Magnetic Bodies, and on That Great Magnet the Earth. In De Magnete, William Gilbert goes over everything under the sun related to magnets and the magnetism of the Earth directly correlating to the invention of the compass some six hundred years before. With his tremendous advancement in research related to magnetism, following many major ideas first put in place by Petrus Perengrinius in his Epistola de magnete, William Gilbert managed to expand on many topics related to geophysics and lay much of the groundwork vital to today’s knowledge of what is to be expected when studying the forces of nature in their whole and specific relation to magnetism. (Hansen, Hall, “The Road to the Magnetic North Pole”). Another well known and world renowned father of the modern beginnings of geophysics and its principles is none other than Sir Isaac Newton, more specifically in his works published in 1687 in his book titled Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). In the Principia Sir Isaac Newton concludes a synopsis of his discoveries in terrestrial and extraterrestrial mechanics, a huge achievement in the history of science and for the world of geophysics. Isaac Newton revealed to humanity his foundation and reasoning for the principles of universal gravitation relating to why things fall on the earth and the movement of the planets, comets, and all other bodies in the cosmos. Isaac Newton breaks down his Principia into three parts, each dedicated to a different area of geophysics. The first dealing completely with his three illustrious laws of motion, the second related to all topics fluid motion related, and the third and final communicating with the systems of the world in correspondence with extraterrestrial bodies and their gravitational relationship in explanation with Kepler’s laws of planetary motion. (Columbia University Press, “The Principia”). Without the justification of geology and naturally occurring events due to the expanses in research with credit to Chang Heng, William Gilbert, and Sir Isaac Newton, many scientists today would not have the pleasure of exploring the vast expansion of the world of geophysics we know today.
Gravity
Branching off from Sir Isaac Newton’s laws of motion, the first of several geophysical topics to be discussed will be gravity. There are basically two ways to approach gravity. Those are gravity in relation to humans here on Earth and then the relationship of the Earth, Moon, and Sun, but they are one in the same. In Newton’s Principia, he classifies gravity as the attractive force between all objects, which explains why the way our universe functions are so vital to our existence. Although it is indeed a myth that an apple falling on his head was his inspiration for gravity, his true motivation did come from an apple. Newton then began to wonder if the same forces that acted upon an apple were the same ones that acted on the moon. But then why is it that the moon continues to hover above the Earth yet the apple plummets to the surface of the Earth? He then realized that the heaviness or weight of an object affected its properties in relation to gravity. Newton defines forces of gravity in the Principia saying:
“Every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them.” –Sir Isaac Newton, Principia What Newton didn’t realize was that he was literally setting the groundwork for more and more discoveries to be made within geophysics. From gravity came studies on planets, stars, galaxies, and even black holes. But even more significantly on Earth, we see the emergence of the study of vibrations, seismic waves, and plate tectonics. (Bellis, “Father of the Science of Electricity & Magnetism”).
Seismic Waves Gravity originates or stems from the center of the Earth. So why is it that we are not collapsing into ourselves as time goes on? Well the answer is that we are. Gravity is a constant force that is acting on all objects on the earth including the rocks and layers that make up the earth. As we move forward through time, parts of rocks beyond the earth’s surface will break suddenly or cause explosions. These explosions get converted into energy that shoot up from layers in the earth that we know as seismic waves which then get recorded on seismographs that we now know originated in China through Chang Heng. There are only two types of seismic waves; surface waves and body waves, which again can be broken down into primary waves and secondary waves. Surface waves are the movements in the ground that we see causes all the devastation. Luckily, the deeper the earthquake occurs, the less of an impact is made from the surface waves. Unfortunately enough though, when these deep eruptions occur on land underneath the ocean, we see tsunami’s much like the one that ravaged the Indian Ocean on December 26th, 2004. Years upon years of energy were being gathered deep beneath the earth’s surface under the sea until finally it could not be contained anymore. The fast moving primary waves were the first to strike the shore, causing a tsunami to be generated at a height of fifty feet and hitting cities at speeds upwards of three hundred miles per hour. And just like with many other quakes of this type, when the disaster was thought to be over, many individuals forget that with a primary wave, there comes a secondary wave which only moves through solid rock, shaking the foundations of many building in cities all along the coast of the Indian Ocean. The possibility of seismic waves moving through solid rock was an incredulous idea to uphold, so scientists concluded that the outer core of the earth is in fact, somewhat liquid in the sense that it is not completely solid. This stems to another idea regarding heat flow throughout he surface of the earth. (Braile, “What Is Seismology”).
Heat Flow The theory of heat flow related to geophysics is a fairly straightforward one and is discussed with the argument of heat transfer. At the very center of the earth are the cores, both outer (liquid) and inner (solid) that achieve heat surmountable to the surface of the sun. Heat escapes from the core and writhes its way up through earth’s interior through the crust by way of conduction. Conduction is merely the transfer of heat between two parts of a stationary system, which is caused by a temperature difference between the parts. Crystal lattice that makes up the rocks in the earth’s crust vibrate rapidly, causing the energy to be transferred upwards and radiated out into the atmosphere. Besides the subliminal methods of heat flow the more obvious and less significant paths (due to the fact that they are so palpable) are dikes, volcanoes, and one probably not very much thought of, hydrothermal activity. The reason why hydrothermal activity is a part of an activity of heat flow is mainly because of the subject matter of sea floor subsidence. The sea floor and its subduction zones are directly affected by heat flow the works it’s way though the mantle and the oceans lithosphere. This heat flow is constantly monitored because an increase in heat and heat flow to the oceans lithosphere would inhibit sea floor subsidence, the ground would never settle and harden to create fresh, new, minty earth. At the same token, a decrease in heat flow would lead to higher cooling rates and much speedier subsidence not allocating enough time or energy for the earth to renew itself. In short it is impossible to deeply involve oneself in studying sea floor subsidence without delving into the methods of understanding heat flow with the oceans lithosphere. (Brown, "Heat Flow"). Another major part of heat flow that many may have overlooked and/or forgotten is the power created by geothermal energy. The future of human civilization and its scientific discipline can see some major advancements in geothermal energy but for now we are limited to building geothermal power plants over naturally occurring geothermal resources. And because heat flow is relatively low through rock, heat gets extracted much faster than the earth has time to replenish it. This means that the lifetime of geothermal resources is limited and incomplete. (Brown, "Heat Flow").
Radioactivity (Geothermal & Geochronology)
The earth that we stand on, that we traverse daily, that we build out houses, apartments, towns, and cities on, that we establish railroads and highways on, that we suck up its precious, valuable, non-renewable natural resources from, this very earth under out feet is probably in itself a very powerful radioactive heat engine. Previously discussed was the geophysical science of heat flow. Heat flow not only directly correlates to the oceanic lithosphere, but also stems from, and with out, would not exist if it weren’t for the earth’s radioactivity. Geothermal activity from radioactive decay in the earth’s crust accounts for nearly nine thousand three hundred megawatts of the world’s electricity generation to sixty million people across twenty-four countries. (Ragheb, “Terrestrial Radioactivity and Geothermal Energy”).
A sibling to radioactivity and geothermal science is the science of geochronology. Breaking down the word simply reveals that geochronology is just the time logging of the earth or more specifically the science that handles the absolute age of rocks and their processes. One very special rock and one covered in this essay previously is the earth’s liquid core which incredulously is made up of rocks heated to the point of practical liquidity. Because of the earth’s magnetic field, a motorized effect is the result of a moving outer core rotation. Radioactivity in the interior of the earth is the foremost critical source of volcanic activity. From a geological standpoint, the core’s rotation has slowed and changed directions several times in the past. Amazingly enough, the core has direct companionship with the earth’s magnetic field, which does several things for all of life’s sustainability on earth including protecting life from solar wind and other various offenses. (Ragheb, “Terrestrial Radioactivity and Geothermal Energy”).
Electricity, Electromagnetic Waves, & Magnetism The planet Earth is quite literally a colossal and oversized magnet with the North and South Pole being the positive and negative ends. Only thing is, the magnetic north and south poles do not line up exactly with the geographic North and South Poles. They can move anywhere from ten to thirty miles depending on earth’s dynamics where the magnetic north and south pole on the giant earth “magnet” point vertically downward. As discussed earlier, the earth’s core is vital to almost all things geophysically and geographically related. The earth creates its own magnetized field from the electrical currents that are created in the liquid iron and nickel core that makes up the outer core of the center of the earth (MacDonald, “Earth’s Magnetism”). So as we know, the outer core of the earth is liquid, so how does this affect the magnetism of the earth? The answer is tremendously. In fact, over the last five million years an amazing phenomenon has taken place and incredulous twenty-five times. What is this amazing occurrence that just occurred a mere 720,000 years ago? Simply by using geology to analyze the magnetic field in minerals, an act known as paeleogeomagnetism, geologists and geophysicists have determined that the two poles will actually change positions. They have also determined that this rare occurrence will most definitely happen again. Because the balance of the earth’s interior is so liquid and unstable, every now and then the magnetic field weakens, the poles will lose their bipolar character and after a few moments they will regenerate and reverse polarity. Some scientists argue that this process takes several thousand years but others, mainly more modern and mainstream scientists disagree and rebutted with a shorter time. One this is for sure, we will know when and how long it takes to complete the process the day all of earths compasses go haywire (Hansen, “The Road to the Magnetic North Pole”).
Geophysics
Geophysics covers a range of ideas from gravity, heat flow, seismic waves that cause vibrations through the Earth’s layers, radioactivity both geothermal and geochronological, electricity, electromagnetic waves and magnetism, fluid dynamics, and even condensed matter physics. Many of these topics were covered so hopefully as the reader you should have an excellent grasp on the topic of geophysics. As stated before, geophysics is a very broad subject, and when peered at under the spotlight, we see that geophysics is no more than a name, a container, for all matters Earthly related and we now see how all of these ideas are valuable to everyone worldwide in getting to know and understand the way our home planet works in relation to ourselves and the space we occupy in the universe.

Works Cited
"Be an Earthquake Detective." Research Foundation of the State of New York (2010). Print.
Bellis, Mary. "Father of the Science of Electricity & Magnetism." The New York Times Company: 1. Print.
Bellis, Mary. "History of the Compass." The New York Times Company: 1-2. Print.
Bellis, Mary. "The Earliest Seismograph." The New York Times Company: 1-2. Print.
Beroza, Greg, Lauren Nelson, and Tora Ilich. "The Department of Geophysics." Stanford University School of Earth Sciences. Print.
Braile, Lawrence. "What Is Seismology." Michigan Technical University. Print.
Brown, Tim, Mike Poulos, and Andy Neigel. "Heat Flow." Boise State University (May 2008). Print.
Columbia University Press. "The Principia." The Columbia Encyclopedia 6th Ed. (2007). Print.
Hansen, Truls Lynne, and Chris Hall. "The Road to the Magnetic North Pole." Ultima Thule University of Tromso.Ravnetrykk.No. 7: 1-10. Print.
Jones, Andrew Zimmerman. "Newton's Law of Gravity." The New York Times Company. Print.
MacDonald, Alexander. “Earth’s Magnetism.” Science on a Sphere. Print
National Geographic. "Deadliest Tsunami in History?" The National Geographic (Jan. 2005). Print.
Ragheb, Magdi. “Terrestrial Radioactivity and Geothermal Energy.” University of Illinois at Urbana-Champaign (Aug. 2008). Print.