Fundamentals of Geography Essay

In geology, a rock is a naturally occurring solid aggregate of one or more minerals or mineraloids. For example, the common rock, granite, is a combination of the quartz, feldspar and biotite minerals. The Earth’s outer solid layer, the lithosphere, is made of rock. Rocks have been used by mankind throughout history. From the Stone Age rocks have been used for tools. The minerals and metals we find in rocks have been essential to human civilization. [1] Three major groups of rocks are defined: igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is an essential component of geology. At a granular level, rocks are composed of grains of minerals, which, in turn, are homogeneous solids formed from a chemical compound that is arranged in an orderly manner. The aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed. Many rocks contain silica (SiO2); a compound of silicon and oxygen that forms 74. 3% of the Earth’s crust. This material forms crystals with other compounds in the rock. The proportion of silica in rocks and minerals is a major factor in determining their name and properties. [2] Rocks are geologically classified according to characteristics such as mineral and chemical composition, permeability, the texture of the constituent particles, and particle size. These physical properties are the end result of the processes that formed the rocks. [3] Over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock:igneous, sedimentary, and metamorphic. The three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks. By increase or decrease in the proportions of their constituent minerals they pass by every gradation into one another, the distinctive structures also of one kind of rock may often be traced gradually merging into those of another. Hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. 4] Igneous Igneous rock (derived from the Latin word igneus meaning of fire, from ignis meaning fire) forms through the cooling and solidification of magma or lava. This magma can be derived from partial melts of pre-existing rocks in either a planet’s mantle or crust. Typically, the melting of rocks is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Igneous rocks are divided into two main categories: plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizesslowly within the Earth’s crust. A common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either aslava or fragmental ejecta, forming minerals such as pumice or basalt. [3] The chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowen’s reaction series, after the Canadian petrologist Norman L. Bowen. Most major igneous rocks are found along this scale. [2] About 64. 7% of the Earth’s crust by volume consists of igneous rocks; making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, and 17% granodiorites and diorites. Only 0. 6% are syenites and 0. 3% peridotites and dunites. The oceanic crust is 99% basalt, which is an igneous rock of mafic composition. Granites and similar rocks, known as meta-granitoids, form much of the continental crust. [5] Over 700 types of igneous rocks have been described, most of them having formed beneath the surface of Earth’s crust. These have diverse properties, depending on their composition and how they were formed. Sedimentary Sedimentary rocks are formed by sedimentation of particles at or near the Earth’s surface and within bodies of water. This process causes clasticsediments or organic particles (detritus) to settle and accumulate, or for minerals to chemically precipitate (evaporite) from a solution. The particulate matter then undergoes compaction and cementation during diagenesis. Before being deposited, sediment was formed by weathering and erosion in a source area, and then transported to the place of deposition by water,wind, ice, mass movement or glaciers which are called agents of denudation. Mud rocks comprise 65% (mudstone, shale and siltstone); sandstones 20 to 25% and carbonate rocks 10 o 15% (limestone and dolostone). [3] About 7. 9% of the crust by volume is composed of sedimentary rocks, with 82% of those being shales, while the remainder consist of limestone (6%), sandstone and arkoses (12%). [5] Metamorphic Metamorphic rocks are formed by subjecting any rock type—sedimentary rock, igneous rock or another older metamorphic rock—to differenttemperature and pressure conditions than those in which the original rock was formed. This process is called metamorphism; meaning to â€Å"change in form†. The result is a profound change in physical properties and chemistry of the stone. The original rock, known as the protolith, transforms into other mineral types or else into other forms of the same minerals, such as by recrystallization. [3] The temperatures and pressures required for this process are always higher than those found at the Earth’s surface: temperatures greater than 150 to 200  °C and pressures of 1500 bars. [6] Metamorphic rocks compose 27. 4% of the crust by volume. [5] The three major classes of metamorphic rock are based upon the formation mechanism. An intrusion of magma that heats the surrounding rock causes contact metamorphism—a temperature-dominated transformation. Pressure metamorphism occurs when sediments are buried deep under the ground; pressure is dominant and temperature plays a smaller role. This is termed burial metamorphism, and it can result in rocks such as jade. Where both heat and pressure play a role, the mechanism is termed regional metamorphism. This is typically found in mountain-building regions. [2] Depending on the structure, metamorphic rocks are divided into two general categories. Those that possess a texture are referred to as foliated; the remainder are termed non-foliated. The name of the rock is then determined based on the types of minerals present. Schists are foliated rocks that are primarily composed of lamellar minerals such as micas. A gneiss has visible bands of differing lightness, with a common example being the granite gneiss. Other varieties of foliated rock include slates, phyllites, and mylonite. Familiar examples of non-foliated metamorphic rocks include marble,soapstone, and serpentine. This branch contains quartzite—a metamorphosed form of sandstone—and hornfels. [2] In geography maps are one of the most important tools researchers, cartographers, students and others can use to examine the entire Earth or a specific part of it. Simply defined maps are pictures of the Earth’s surface. They can be general reference and show landforms, political boundaries, water, the locations of cities, or in the case of thematic maps, show different but very specific topics such as the average rainfall distribution for an area or the distribution of a certain disease throughout a county. Today with the increased use of GIS, also known as Geographic Information Systems, thematic maps are growing in importance. There are however applications for different types of general reference maps when the different types are understood correctly. These maps do not just show a city’s location for example; instead the different map types can show a plethora of information about places around the world. The following is a list of each major map type used by geographers and a description of what they are and an example of each kind. †¢ Political Map: A political map does not show any topographic features. It instead focuses solely on the state and national boundaries of a place. They also include the locations of cities – both large and small, depending on the detail of the map. A common type of political map would be one showing the 50 U.  S. states and their borders along with the United States’ north and south international borders (map of the United States). †¢ Physical Map: A physical map is one that shows the physical landscape features of a place. They generally show things like mountains, rivers and lakes and water is always shown with blue. Mountains and elevation changes are usually shown with different colors and shades to show relief. Normally on physical maps green shows lower elevations while browns show high elevations. An example of a physical map is one showing the state of Hawaii (map of Hawaii). Low elevation coastal regions are shown in dark green, while the higher elevations transition from orange to dark brown. Rivers are shown in blue. †¢ Topographic Map: A topographic map is similar to a physical map in that it shows different physical landscape features. They are different however because they use contour lines instead of colors to show changes in the landscape. Contour lines on topographic maps are normally spaced at regular intervals to show elevation changes (e. g. each line represents a 100 foot (30 m) elevation change) and when lines are close together the terrain is steep. For example a topographic map showing the Big Island of Hawaii would have contour lines that are close together near the steep, high elevation mountains of Mauna Loa and Kilauea (map of the Big Island). By contrast, the low elevation, flat coastal areas show contour lines that are spread apart. †¢ Climate Map: A climate map shows information about the climate of an area. They can show things like the specific climatic zones of an area based on the temperature, the amount of snow an area receives or average number of cloudy days. These maps normally use colors to show different climatic areas. A climate map for Australia for example uses colors to show differences between the temperate area of Victoria and desert region in the center of the continent. †¢ Economic or Resource Map: An economic or resource map shows the specific type of economic activity or natural resources present in an area through the use of different symbols or colors depending on what is being shown on the map. For example an economic activity map for Brazil can use colors to show different agricultural products of given areas, letters for natural resources and symbols for different industries (image showing a map of Brazil). Road Map: A road map is one of the most widely used map types. These maps show major and minor highways and roads (depending on detail) as well as things like airports, city locations and points of interest like parks, campgrounds and monuments. Major highways on a road map are generally red and larger than other roads, while minor roads are a lighter color and a narrower line. A road map of San Francisco, California for example would show the major highways as a wide red line and other large roads as a lighter red with minor streets as gray (map of San Francisco). Thematic Map: A thematic map is a map that focuses on a particular theme or special topic and they are different from the six aforementioned general reference maps because they do not just show natural features like rivers, cities, political subdivisions, elevation and highways. If these items are on a thematic map, they are background information and are used as reference points to enhance the map’s theme. An example of a thematic map would be one showing the population change of Canada in specific locations from 1996 to 2001. The map shows the theme it is attempting to get across to its audience and uses a political map (e. g. one showing the provincial and territorial borders of Canada) to give it more of a reference. What Is the Difference Between Weather and Climate? It’s a sweltering midsummer day. â€Å"It must be global warming,† mutters someone. But is it the Earth’s changing climate that has made the day so warm? Or, is it just the weather that is so unbearable? Weather is the mix of events that happen each day in our atmosphere including temperature, rainfall and humidity. Weather is not the same everywhere. Perhaps it is hot, dry and sunny today where you live, but in other parts of the world it is cloudy, raining or even snowing. Everyday, weather events are recorded and predicted by meteorologists worldwide. Climate in your place on the globe controls the weather where you live. Climate is the average weather pattern in a place over many years. So, the climate of Antarctica is quite different than the climate of a tropical island. Hot summer days are quite typical of climates in many regions of the world, even without the effects of global warming. Climates are changing because our Earth is warming, according to the research of scientists. Does this contribute to a warm summer day? It may, however global climate change is actually much more complicated than that because a change in the temperature can cause changes in other weather elements such as clouds or precipitation. Atmospheric circulation is the large-scale movement of air, and the means (together with the smaller ocean circulation) by whichthermal energy is distributed on the surface of the Earth. The large-scale structure of the atmospheric circulation varies from year to year, but the basic climatological structure remains fairly constant. Individual weather systems – mid-latitude depressions, or tropical convective cells – occur â€Å"randomly†, and it is accepted that weather cannot be predicted beyond a fairly short limit: perhaps a month in theory, or (currently) about ten days in practice (see Chaos theory and Butterfly effect). Nonetheless, as the climate is the average of these systems and patterns – where and when they tend to occur again and again – it is stable over longer periods of time. As a rule, the â€Å"cells† of Earth’s atmosphere shift polewards in warmer climates (e. g. nterglacials compared to glacials), but remain largely constant even due to continental drift; they are, fundamentally, a property of the Earth’s size, rotation rate, heating and atmospheric depth, all of which change little. Tectonic uplift can significantly alter major elements of it, however – for example the jet stream -, and plate tectonics shift ocean currents. In t he extremely hot climates of the Mesozoic, indications of a third desert belt at the Equator has been found; it was perhaps caused by convection. But even then, the overall latitudinal pattern of Earth’s climate was not much different from the one today. The wind belts girdling the planet are organised into three cells: the Hadley cell, the Ferrel cell, and the Polar cell. Contrary to the impression given in the simplified diagram, the vast bulk of the vertical motion occurs in the Hadley cell; the explanations of the other two cells are complex. Note that there is one discrete Hadley cell that may split, shift and merge in a complicated process over time[citation needed]. Low and high pressures on earth’s surface are balanced by opposite relative pressures in the upper troposphere.