Latitude, Longitude and Time Zones
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Latitude, Longitude and Time Zones
Longitude and latitude are imaginary lines that circle the Earth. They are used to exactly pinpoint where a person or object is located. These lines are located on maps and measured in degrees. Each degree is divided into 60 minutes and each minute has 60 seconds.
Latitude describes east-west lines that circle the Earth parallel to the equator. Any point along the equator has a latitude of 0°. While the equator is the longest of these lines, they become shorter the farther you move to the poles, which have a latitude of 90°. The equator divides the earth into a northern and southern hemisphere. Each degree has the same distance, roughly 69 miles (111 km).
On its way around the sun, the Earth tilts its axis towards and away from it. This is the reason for special lines of latitude:
- Tropic of Cancer (23 ½ ° north of the equator) – the sun appears directly overhead in June
- Tropic of Capricorn (23 ½ ° south of the equator) – the sun appears directly overhead in December
- Arctic Circle (66 ½ ° north of the equator) – the sun is constantly above the horizon in June. Daylight lasts for 24 hours in June.
- Antarctic Circle (66 ½ ° south of the equator) - the sun is constantly above the horizon in December. Daylight lasts for 24 hours.
Longitude and Latitude
Longitude or meridians are lines that run from north to south across the globe. The starting point for this system (0°) is the British Royal Observatory in Greenwich, England. This prime meridian was chosen at a time when England was dominant in making maps and navigating. Locations west of this line have a longitude of up to 179° west; those to the east have a longitude of up to 179° east. The 180th meridian is exactly on the oppositeside of the globe, in the middle of the Pacific Ocean. This is also the International Date Line. Travellers who travel westwards across the dateline change to the following day.
The distance between each degree of longitude varies. It is largest at the equator (69 miles) and shortest at the poles (0 miles) where the lines come together there.
Coordinates are numbers that locate a certain point on this system. New York, for example, lies at 41° North and 74° West. While navigators in the Middle Ages and during the Age of Exploration used sextants and the stars to determine their location, we use satellites and GPS to pinpoint our exact location anywhere on earth.
Time Zones
Because the earth rotates around its axis once a day, it is divided into 24 different time zones. The starting point for these time zones is the prime meridian in Greenwich, also called Greenwich Mean Time. Theoretically, every 15° east or west of Greenwich means one hour more or less. In practice, however, time zones do not go through the middle of countries.
Larger countries that span thousands of km, for example Russia or the United States, have several time zones. On the other hand, the Chinese Communists changed the country to one time zone when they took over after World War II.
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Rock
Rock is the hard material that most of the earth’s crust is made up of. Mountains, coastlines, valleys and plains are made up of different kinds of rock. In some places soil lies over rock formations. They are often eroded and made smaller during the course of the earth’s history. Sometimes broken parts of rock lie on top of the earth’s surface. Tiny bits of them make up sand or soil. Most rocks contain crystals of two or more different minerals. Granite for example contains grains of quartzand feldspar.
People use rocks for many different things. They play an important role in the construction industry. Concrete, for example, is made up of stones, sand and gravel and mixed with cement. Rocks are also used to make medicine, weapons and cosmetics. Various types of rock have been used to make historic monuments, like the ancient Egyptian pyramids.
Rock that contains metals is called ore. Iron, copper, lead, gold, and uranium are among the most important ores. Aluminum is produced out of a rock called bauxite. Other rocks contain valuable minerals, like diamonds or other gems.
Geologists are scientists who study the origin and composition of rocks. This gives them more information on the history of our planet. Rocks can also reveal how life evolved and which events shaped the Earth and the solar system.
Rocks are often classified by their hardness. They may be soft like talc, which you can scratch with your fingernail. On the other side of the scale diamonds are the hardest known rocks on earth. They are used to cut other minerals or in oil drilling.
Geologists often identify rocks by studying their formations. These often contain fossils that show scientists how old the rock may be. 
Types of rock
Igneous rock
Igneous rock is hot molten rock that comes from below the earth’s surface. It forms when magma comes to the surface from cracks in the Earth’s crust. When it emerges through pipes and erupts volcanoes are formed. Such rock hardens quickly when it cools down. Dark colored igneous rocks are called basalts. They are formed either on the ocean’s floor or where lava flows occur.
Granite is a gray or white igneous rock that crystallizes slowly below the earth’s surface. It is often used as building materials and in homes.
Sedimentary rock
Sediments are small pieces of rock that are transported by wind, water or glaciers. In the course of their movement they break apart into smaller pieces.
Sedimentary rock is formed when a river carries pieces of broken rock along with it and slowly deposits them onto its bed. On the ocean floor, dead plants and animals are deposited during the course of millions of years. These organic sediments harden and turn into rock.
Sandstone and limestone are two of the most important and widespread sedimentary rocks. These sediments contain fossil fuels, like oil and gas. Limestone is made up of shells and skeletons of living things. It forms in shallow ocean water. The white cliffs of Dover are the most famous natural limestone areas on earth. Sandstone is made up of quartz that has been pressed over the ages. It is often white or yellowish.
Metamorphic rock
Metamorphic rock is rock that changes through heat and pressure in the deeper layers in the earth. The minerals in these rocks are chemically changed. Granite for example is turned into gneiss. Limestone turns into marble and sandstone can turn into quartzite.
Folding in a Metamorphic Rock
Rock cycle
Rock is formed, destroyed and reformed in a cycle. It breaks into pieces through erosion. These pieces settle down onto the floor of oceans and rivers and become sedimentary rock. When such rock sinks deeper and deeper it turns into metamorphic rock.
Pressure can bring such rock to the surface where it can erupt in the form of volcanoes. On the surface rock breaks down again through erosion and is transported in rivers and streams. The cycle then starts from the beginning.
Such a rock cycle takes millions of year to complete.
The Rock Cycle