Earth Sciences Earth science (also known as geoscience , the geosciences or the Earth Sciences ), is an all-embracing term for the sciences related to the planet Earth. It is arguably a special case in planetary science, the Earth being the only known life-bearing planet. There are both reductionist and holistic approaches to Earth science. There are four major disciplines in earth sciences, namely geography, geology, geophysics and geodesy. These major disciplines use physics, chemistry, biology, chronology and mathematics to build a quantitative understanding of the principal areas or spheres of the Earth system.
Environmental Sciences Environmental science is an expression encompassing the wide range of scientific disciplines that need to be brought together to understand and manage the natural environment and the many interactions among physical, chemical, and biological components. Environmental Science provides an integrated, quantitative, and interdisciplinary approach to the study of environmental systems. Individuals may operate as Environmental scientists or a group of scientists may work together pooling their individual skills. The most common model for the delivery of Environmental science is through the work of an individual scientist or small team drawing on the peer-reviewed, published work of many other scientists throughout the world.
Aristotle Aristotle’s theory of the basic constituents of matter looks to a modern scientist perhaps something of a backward step from the work of the atomists and Plato. Aristotle assumed all substances to be compounds of four elements : earth, water, air and fire, and each of these to be a combination of two of four opposites , hot and cold, and wet and dry. (Actually, the words he used for wet and dry also have the connotation of softness and hardness). Aristotle’s whole approach is more in touch with the way things present themselves to the senses, the way things really seem to be, as opposed to abstract geometric considerations. Hot and cold, wet and dry are qualities immediately apparent to anyone, this seems a very natural way to describe phenomena. He probably thought that the Platonic approach in terms of abstract concepts, which do not seem to relate to our physical senses but to our reason, was a completely wrongheaded way to go about the problem. It has turned out, centuries later, that the atomic and mathematical approach was on the right track after all, but at the time, and in fact until relatively recently, Aristotle seemed a lot closer to reality. He discussed the properties of real substances in terms of their “elemental” composition at great length, how they reacted to fire or water, how, for example, water evaporates on heating because it goes from cold and wet to hot and wet, becoming air, in his view. Innumerable analyses along these lines of commonly observed phenomena must have made this seem a coherent approach to understanding the natural world.
Galileo Galilei <ul><li>A biography by Galileo's pupil Vincenzo Viviani stated that Galileo had dropped balls of the same material, but different masses, from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass.  This was contrary to what Aristotle had taught: that heavy objects fall faster than lighter ones, in direct proportion to weight.  While this story has been retold in popular accounts, there is no account by Galileo himself of such an experiment, and it is generally accepted by historians that it was at most a thought experiment which did not actually take place. </li></ul><ul><li>Galileo proposed that a falling body would fall with a uniform acceleration, as long as the resistance of the medium through which it was falling remained negligible, or in the limiting case of its falling through a vacuum. </li></ul>
Johannes Kepler <ul><li>Kepler's First Law: All planets move about the sun in an elliptical orbit with the sun at one foci. In an elliptical orbit the distance between the planet and the sun is continuously varying. </li></ul><ul><li>Keplers Second Law: Equal Areas in Equal Times </li></ul><ul><li>Keplers Third Law: The Harmonic law </li></ul><ul><ul><li>In the above P is the orbital period measured in years and A is the semi-major axis measured in units of AU (the distance from the earth to the Sun). This empirical expression sets the scale of the solar system. For instance, if I observe an object to have an orbital period of 8 years then I know that it must have a semi-major axis of 4 AU, by the above expression. This solution is shown below: </li></ul></ul><ul><ul><li>1 Astronomical Unit = 149 598 000 kilometers </li></ul></ul>
Robert Boyle <ul><li>Boyle’s Gas Law: </li></ul><ul><ul><li>For a fixed amount of an ideal gas kept at a fixed temperature, P [pressure] and V [volume] are inversely proportional (while one increases, the other decreases). </li></ul></ul><ul><li>The relationship between pressure and volume was brought to the attention of Robert Boyle by two friends and amateur scientists, Richard Towneley and Henry Power, who discovered it. Boyle confirmed their discovery through experiments and published the results. According to Robert Gunther and other authorities, it was Boyle's assistant Robert Hooke, who built the experimental apparatus. Boyle's law is based on experiments with air, which he considered to be a fluid of particles at rest, with in between small invisible springs. At that time air was still seen as one of the four elements, but Boyle didn't agree. Probably Boyle's interest was to understand air as an essential element of life  ; he published e.g. the growth of plants without air  . The French physicist Edme Mariotte (1620-1684) discovered the same law independently of Boyle in 1676, so this law may be referred to as Mariotte's or the Boyle-Mariotte law. Later (1687) in the Philosophiæ Naturalis Principia Mathematica Newton showed mathematically that if an elastic fluid consisting of particles at rest, between which are repulsive forces inversely proportional to their distance , the density would be proportional to the pressure  , but this mathematical treatise is not the physical explanation for the observed relationship. Instead of a static theory a kinetic theory is needed, which was provided two centuries later by Maxwell and Boltzmann. </li></ul>
Sir Isaac Newton <ul><li>Laws of Motion </li></ul><ul><ul><li>Newton's first law states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force . This is normally taken as the definition of inertia. The key point here is that if there is no net force acting on an object (if all the external forces cancel each other out) then the object will maintain a constant velocity . If that velocity is zero, then the object remains at rest. If an external force is applied, the velocity will change because of the force. </li></ul></ul><ul><ul><li>The second law explains how the velocity of an object changes when it is subjected to an external force. The law defines a force to be equal to change in momentum (mass times velocity) per change in time . Newton also developed the calculus of mathematics, and the "changes" expressed in the second law are most accurately defined in differential forms. (Calculus can also be used to determine the velocity and location variations experienced by an object subjected to an external force.) For an object with a constant mass m , the second law states that the force F is the product of an object's mass and its acceleration a : F = m * a </li></ul></ul><ul><ul><li>The third law states that for every action (force) in nature there is an equal and opposite reaction . In other words, if object A exerts a force on object B, then object B also exerts an equal force on object A. Notice that the forces are exerted on different objects. The third law can be used to explain the generation of lift by a wing and the production of thrust by a jet engine. </li></ul></ul>
Benjamin Franklin & Michael Faraday <ul><li>In 1750, he published a proposal for an experiment to prove that lightning is electricity by flying a kite in a storm that appeared capable of becoming a lightning storm. On May 10, 1752, Thomas-François Dalibard of France conducted Franklin's experiment using a 40-foot (12 m)-tall iron rod instead of a kite, and he extracted electrical sparks from a cloud. On June 15, Franklin may have possibly conducted his famous kite experiment in Philadelphia and also successfully extracted sparks from a cloud, although there are theories that suggest he never performed the experiment. </li></ul><ul><li>When Michael Faraday made his discovery of electromagnetic induction in 1831, he hypothesized that a changing magnetic field is necessary to induce a current in a nearby circuit. To test his hypothesis he made a coil by wrapping a paper cylinder with wire. He connected the coil to a galvanometer, and then moved a magnet back and forth inside the cylinder. </li></ul>
Count Rumford <ul><li>In the seventeenth century, scientists held a clear association between heat and motion of constituent particles. Heat became recognized as a fluid that flowed from hot objects to cold ones. During Galileo's time, this heat fluid was known as phlogiston and was considered the soul of matter . Phlogiston had mass and was released by or absorbed by an object when burning. In the late eighteenth century Antoine Lavoisier refined the view that heat was a liquid, overthrew the current phlogiston theory, and developed the caloric theory of heat. In 1787 Lavoisier coined the term caloric to represent the heat fluid. Caloric was thought to be massless, colorless and conserved in total in the universe . The individual particles making up the fluid were elastic and repelled each other but were attracted by particles of other substances, the magnitude of the attraction being different for different substances. It was thought that caloric could be "sensible" in that it diffused among the particles of the material it was acting upon thereby surrounding each particle with an atmosphere of caloric. </li></ul><ul><li>It could also combine with the particles of the material in a manner similar to chemical combinations and be "latent." By the beginning of the nineteenth century most scientists accepted the caloric theory as the correct theory of heat. The theory offered many plausible explanations regarding heat transfer where other theories had failed. It was a simple theory and had many successful applications. These facts made the theory widely accepted but also made it extremely difficult to overthrow. </li></ul><ul><li>Because the caloric theory was so powerful, it took some 50 years to overthrow. A dispute rumbled concerning whether caloric had weight . Benjamin Thompson showed that cooling and heating of a substance had no detectable effect on its weight. He studied the heat produced by friction in boring of cannons in 1798 and showed that just as much heat was produced when a blunt boring tool was used and no metal was cut as when a sharp instrument was employed. It appeared that the heat produced by friction was inexhaustible, and, therefore, not a conserved quantity as required by caloric theory. Thompson continued his attacks on the caloric theory into the early nineteenth century. Eventually, in the 1840s, James Joule explained the source of heating in Thompson's experiments and recognized that heat is another form of energy , resulting from the motion or kinetic energy of atoms and molecules. This led to the downfall of the caloric theory and formation of the principle of conservation of energy , and the kinetic theory of heat. </li></ul>
James Prescott Joule <ul><li>In addition to his work on the conservation of energy, Joule made a number of other important contributions to physics. In 1846 he discovered the phenomenon of magnetostriction, in which an iron rod was found to change its length slightly when magnetized. In 1852, together with William Thomson, he showed that when a gas is allowed to expand into a vacuum, its temperature drops slightly. This "Joule-Thomson effect" is still very useful in the production of low temperatures. </li></ul><ul><li>Joule believed that nature was ultimately simple, and strove to find the simple relationships (like Joule's law in electricity), which he was convinced must exist between important physical quantities. His phenomenal success in finding such relationships in the laboratory made a crucial contribution to the understanding of energy and its conservation in all physical, chemical and biological processes. </li></ul>
Augustin Jean Fresnel & Thomas Young <ul><li>Augustin-Jean Fresnel (pronounced /freɪˈnɛl/ fray-NELL, French pronunciation: [ɔɡystɛ̃ ʒɑ̃ fʁɛnɛl]; 10 May 1788 – 14 July 1827), was a French physicist who contributed significantly to the establishment of the theory of wave optics. Fresnel studied the behaviour of light both theoretically and experimentally. He is perhaps best known as the inventor of the Fresnel lens, first adopted in lighthouses while he was a French commissioner of lighthouses, and found in many applications today. </li></ul><ul><li>In Young's own judgment, of his many achievements the most important was to establish the wave theory of light. To do so, he had to overcome the century-old view, expressed in the venerable Isaac Newton's "Optics", that light is a particle. Nevertheless, in the early 1800s Young put forth a number of theoretical reasons supporting the wave theory of light, and he developed two enduring demonstrations to support this viewpoint. With the ripple tank he demonstrated the idea of interference in the context of water waves. </li></ul>
James Clerk Maxwell <ul><li>James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish theoretical physicist and mathematician. His most significant achievement was the development of the classical electromagnetic theory, synthesizing all previous unrelated observations, experiments and equations of electricity, magnetism and even optics into a consistent theory. </li></ul><ul><li>Maxwell demonstrated that electric and magnetic fields travel through space in the form of waves, and at the constant speed of light. Finally, in 1864 Maxwell wrote A Dynamical Theory of the Electromagnetic Field where he first proposed that light was in fact undulations in the same medium that is the cause of electric and magnetic phenomena. His work in producing a unified model of electromagnetism is considered to be one of the greatest advances in physics. </li></ul>
Albert Einstein & Max Planck <ul><li>Theory of Relativity - The theory of relativity , or simply relativity , generally refers specifically to two theories of Albert Einstein: special relativity and general relativity. </li></ul><ul><ul><li>Special Relativity - Special relativity is based on two postulates which are contradictory in classical mechanics: The laws of physics are the same for all observers in uniform motion relative to one another (Galileo's principle of relativity), The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the source of the light. </li></ul></ul><ul><ul><li>General Relativity - The development of general relativity began with the equivalence principle, under which the states of accelerated motion and being at rest in a gravitational field (for example when standing on the surface of the Earth) are physically identical. </li></ul></ul><ul><li>Quantum Theory </li></ul><ul><ul><li>quantum theory modern physical theory concerned with the emission and absorption of energy by matter and with the motion of material particles; the quantum theory and the theory of relativity together form the theoretical basis of modern physics. Just as the theory of relativity assumes importance in the special situation where very large speeds are involved, so the quantum theory is necessary for the special situation where very small quantities are involved, i.e., on the scale of molecules , atoms , and elementary particles . Aspects of the quantum theory have provoked vigorous philosophical debates concerning, for example, the uncertainty principle and the statistical nature of all the predictions of the theory. </li></ul></ul>