As humans, we experience the effects of chemistry, biology and physics every day, but not always knowingly. Geography is the most sensual of the hard sciences, the one that allows us to better understand our immediate environment.
Basic Geography and Geology Knowledge Checklist
Layers of the earth: Outer crust, mantle (viscous), outer core (liquid metal), inner core (solid metal)
Earth’s crust: The surface of the earth that is made of various rocks and minerals with soil on top. The five main elements found in the Earth’s crust are oxygen, silicon, aluminum, iron, calcium.
Rock: Collections of minerals formed together into a stone. A compound.
Mineral: A single material of uniform color, texture, luster and structure. Usually made up of two or more elements.
Crystal: A piece of mineral that has a characteristic shape (box or cube). Ex: table salt. Each grain of salt is cube-shaped. Each molecule, too.
Dirt: They are made up of broken down minerals and organic substances through weathering.
Soil: Dirt that is fit to grow plants in
Ore: Any natural, earth material that is mined and processed to obtain a desired metal. Ex: iron ore is rock containing iron.
Metal: The chemical particles, often found in minerals, that are pure metallic elements such as iron, copper, gold and aluminum. They share these properties: 1. shiny; 2. conduct heat and electricity; 3. solid at room temp (except mercury); 4. some are magnetic (iron and nickel).
Alloy: A mixture of two or more metals
Steel: An alloy of iron, carbon and traces of other metals
Sediment: The dirt and sand that is carried away with water and wind and add layers to other places. The layers separate according to the size and density of the materials and eventually harden into rock under the sea and elsewhere.
Fossil: The structure that results when organisms are buried under layers of sediment and pressed on, then cemented into the soil
Clay: A kind of dirt with the smallest particles. Makes a very uniform, soft sdimentary rock, like shale … unlike sandstone. Clay soil holds water well.
The three types of rocks: Sedimentary, igneous and metamorphic
Sedimentary rock: Rock formed when other rocks break down into sediment, then gradually reform other rocks due to pressure and layering. The Grand canyon is an example of sedimentary rocks. Its layers are visible. It was once under the ocean.
Igneous rock: Rock formed from magma erupting from a volcano. It forms in an irregular, crystalline pattern combining two or more distinct materials, with less mixing. Come from cooling magma, so form quickly and doesn’t contain fossils.
Metamorphic rock: Igneous, sedimentary or other metamorphic rock that changes due to heat
Corrosion: The damaging chemical reaction that occurs when metal is in contact with oxygen. The damage happens because oxide forms on the metal.
Weathering: The process of the breakdown of minerals, rocks and organic materials through freezing, thawing, melting, abrasion, wind, acids, etc.
Water: A chemical compound that is the most common liquid on earth. It is a solvent that is formed when hydrogen burns in air (oxygen).
The water cycle: The process by which water is continuously recycled between the earth, the atmosphere and living things through heat and evaporation and clouds and rain
Dissolve: To mix something into a liquid
Solution: The result of dissolving something in a liquid
Soluble: Able to dissolve in liquid
Insoluble: Unable to dissolve in liquid
Tides: The rise and fall of sea levels caused by the gravity of the moon and the rotation of the earth
Air: The gas that we breathe. Air is oxygen, nitrogen and carbon dioxide. It helps people breathe oxygen, which they need in their blood. It helps plants make food. It protects people from sun’s UV rays. Nitrogen: 78%, Oxygen – 21%, Other – 1%. Molecules/particles in air are constantly moving and there’s lots of empty space between them. Like water always flows downhill, air always flows toward lower pressure. To separate out the gases in air, just cool and compress it. Each gas liquifies at a different temperature.
Earth’s atmosphere: All of the air that surrounds the Earth. It is held near the earth due to gravity. There is no distinct starting point, but instead a gradual decline; the further up into the atmosphere you get, the less air is held down. Also, the higher air is thinner, with less oxygen, and unbreathable. (Side note: the moon’s gravitational pull isn’t strong enough to hold air down, so there is no air on the moon.)
Air compression: What happens when air particles are pushed closer together (as in a small space). Compressed air is more highly pressurized.
Air pressure: The condition created when air is pushed. When you push more air into a small space, air particles move closer together but try to escape by pushing on the inside walls (of the tire or balloon or whatever). The place on the body we notice air pressure changes is the ear since the eardrum must have equal air pressure on both sides, but air has to go through a bottleneck, and can move unevenly, resulting in popping.
Vacuum: When we suck or otherwise remove air from a container, we create a vacuum. By removing air, air pressure decreases. And since air always flows toward lower pressure, sucking occurs and air and materials from the outside get pulled in. (It’s not the motion of pulling out the air that causes sucking. It’s the higher pressure on the outside wanting to get in!) Outer space has no air, so it is a vaccum. If you went to space without a spacesuit you’d explode because all the air in your body would push outward toward the vaccum at once. Spacesuits provide air pressure.
Ecosystem: A group of plants and animals that interact with each other and their surroundings
Biome: A unique climate and soil type
The eleven biomes of Earth: Tropical rainforests, deciduous forests, mountains, coniferous forests, scrub lands, temperate grasslands/prairies, tundra, tropical grasslands, deserts, polar areas, oceans
Habitat: The natural environment in which a species lives
Biodiversity: The huge variety of living things in a particular area. Biodiversity is lost with selective breeding.
Pollution: The unneeded junk (particularly the human-made chemical particles) that gets into the air and water. Water pollution happens both due to poisons in water killing life and to the oxygen in the water being used up by the bacteria (or even plant) overgrowth as they feed on waste materials. When there is inadequate oxygen for fish and animals, the water becomes lifeless.
The Ozone Layer: The layer of ozone (O3) that exists in the upper atomosphere of earth. It is poisonous to humans but protects us from UV rays.
The Greenhouse Effect: The result of an overabundance of carbon dioxide in the atmosphere, which traps heat and causes a greenhouse-like effect on earth which then results in major climate change
Global warming: The result of the Greenhouse Effect
Sewage treatment: The process by which a city’s waste water is filtered for large particles, then left in tanks where the organic solids sink to the bottom and are broken down by bacteria
Carbon cycle: The process by which carbon cycles in an through plants, animals, minerals and the atmosphere. This happens mostly due to the respiration of carbon dioxide by animals, the incorporation of carbon dioxide by plants during photosynthesis, decomposition and the burning of fossil fuels.
Nitrogen cycle: When the nitrogen cycle is not in balance, global warming and ozone depletion can occur.
Intensive farming: Farming with use of chemicals, machinery, etc.
Earth Zones: Arctic and Antarctic; North and South Temperate; tropical (the middle, both sides of equator)
U.S. states, capitals, major cities, major rivers, mtns, countries of all continents, major climate regions and crops that grow there, biggest cities by pop and countries by land and pop
types of govn’t
Imaginary lines running horizontally around the globe. Also called parallels, latitude lines are equidistant from each other. Each degree of latitude is about 69 miles (110 km) apart. Zero degrees (0°) latitude is the equator, the widest circumference of the globe. Latitude is measured from 0° to 90° north and 0° to 90° south—90° north is the North Pole and 90° south is the South Pole.
Imaginary lines, also called meridians, running vertically around the globe. Unlike latitude lines, longitude lines are not parallel. Meridians meet at the poles and are widest apart at the equator. Zero degrees longitude (0°) is called the prime meridian. The degrees of longitude run 180° east and 180° west from the prime meridian.
Latitude and longitude lines form an imaginary grid over the Earth’s surface. By combining longitude and latitude measurements, any location on earth can be determined. The units of measurement for geographic coordinates are degrees (°), minutes (‘), and seconds (“). Like a circle, the Earth has 360 degrees. Each degree is divided into 60 minutes, which in turn is divided into 60 seconds. Latitude and longitude coordinates also include cardinal directions: north or south of the equator for latitude, and east or west of the prime meridian for longitude. The geographic coordinates of New York City, for example, are 40° N, 74° W, meaning that it is located 40 degrees north latitude and 74 degrees west longitude. Using minutes and seconds as well as degrees, the coordinates for New York would be 40°42’51” N, 74°0’23” W. (Latitude is always listed first.) A less common format for listing coordinates is in decimal degrees. The Tropic of Cancer, for example, can be expressed in degrees and minutes (23°30’ N) or in decimal degrees (23.5° N).
A hemisphere is half the Earth’s surface. The four hemispheres are the Northern and Southern hemispheres, divided by the equator (0° latitude), and the Eastern and Western hemispheres, divided by the prime meridian (0° longitude) and the International Date Line (180°).
Zero degrees latitude. The Sun is directly overhead the equator at noon on the two equinoxes (March and Sept. 20 or 21). The equator divides the globe into the Northern and Southern hemispheres. The equator appears halfway between the North and South poles, at the widest circumference of the globe. It is 24,901.55 miles (40,075.16 km) long.
Zero degrees longitude (0°). The prime meridian runs through the Royal Greenwich Observatory in Greenwich, England (the location was established in 1884 by international agreement). The prime meridian divides the globe into the Western and Eastern hemispheres. The Earth’s time zones are measured from the prime meridian. The time at 0° is called Universal Time (UT) or Greenwich Mean Time (GMT). With the Greenwich meridian as the starting point, each 15° east and west marks a new time zone. The 24 time zones extend east and west around the globe for 180° to the International Date Line. When it is noon along the prime meridian, it is midnight along the International Date Line.
International Date Line
Located at 180° longitude (180° E and 180° W are the same meridian). Regions to the east of the International Date Line are counted as being one calendar day earlier than the regions to the west. Although the International Date Line generally follows the 180° meridian (most of which lies in the Pacific Ocean), it does diverge in places. Since 180° runs through several countries, it would divide those countries not simply into two different time zones, but into two different calendar days. To avoid such unnecessary confusion, the date line dips and bends around countries to permit them to share the same time.
Tropic of Cancer
A line of latitude located at 23°30′ north of the equator. The Sun is directly overhead the Tropic of Cancer on the summer solstice in the Northern Hemisphere (June 20 or 21). It marks the northernmost point of the tropics, which falls between the Tropic of Cancer and the Tropic of Capricorn.
Tropic of Capricorn
A line of latitude located at 23°30′ south. The Sun is directly overhead the Tropic of Capricorn on the summer solstice in the Southern Hemisphere (Dec. 20 or 21). It marks the southernmost point of the tropics.
A line of latitude located at 66°30′ north, delineating the Northern Frigid Zone of the Earth.
A line of latitude located at 66°30′ south, delineating the Southern Frigid Zone of the Earth.
The most accurate map of the Earth, duplicating its spherical shape and relative size.
Two-dimensional representations of the three-dimensional Earth. Because projections attempt to present the spherical Earth on a flat plane, they inevitably produce distortions. Map projections are numerous and complex (e.g., there are a variety of cylindrical, conic, or azimuthal projections). Each projection has advantages and serves different purposes, and each produces different types of distortions in direction, distance, shape, and relative size of areas. One of the most famous projections is the Mercator, created by Geradus Mercator in 1569. It is a rectangular-shaped map in which all longitude and latitude lines are parallel and intersect at right angles (on a globe, meridians are not parallel, but grow narrower, eventually converging at the poles). Near the equator, the scale of the Mercator is accurate, but the farther one moves toward the poles, the greater the distortion—Antarctica in the far south and Greenland in the far north, for example, appear gigantic. The Mercator projection was used well into the 20th century, but has now been superseded by others, including the widely used Robinson projection. The Robinson projection is an elliptical-shaped map with a flat top and bottom. Developed in 1963 by Arthur H. Robinson, it is an orthophanic (“right appearing”) projection, which attempts to reflect the spherical appearance of the Earth. The meridians, for example, are curved arcs, which gives the flat map a three-dimensional appearance. But to convey the likeness of a curved, three-dimensional globe, the Robinson projection must in fact distort shape, area, scale, and distance. The Albers, Lambert, Mollweide, and Winkel Tripel are some of the other commonly used map projections.
Despite its being called “Earth,” more than two-thirds of our planet’s surface is covered in water. The rest consists of seven vast expanses of land called continents. The largest of these is Asia, followed by Africa, North America, South America, Antarctica, Europe, and Australasia. They contain an amazing variety of landscapes—mountains, deserts, tropical rainforests, woodlands, and polar ice caps.
Seventy-one percent of our planet is covered with water in the form of oceans, seas, lakes, and rivers. The highest mountain, the deepest trench, and the longest mountain range are all found under the ocean.
FACTFILE: PHYSICAL WORLD
Longest river: Nile 4,160 miles (6,695 km)
Largest lake: Caspian Sea 143,243 sq miles (371,000 sq km)
Highest point: Mt. Everest 29,035 ft (8,850 m)
Lowest point: Dead Sea –1,312 ft (–400 m)
Largest ocean: Pacific Ocean
Largest desert: Sahara 3,263,400 sq miles (9,065,000 sq km)
Largest island: Greenland 836,327 sq miles (2,166,086 sq km)
Coldest place: Ulan Bator, Mongolia –26°F (–32°C)
Hottest place: Baghdad, Iraq 110°F (43°C), July/August
Wettest place: (by annual rainfall) Liberia, 202 in (514 cm) of rain per year
Driest place: (by annual rainfall) Egypt, 11°8 in (2.9 cm) of rain per year
The world today is divided into 193 independent nations, differing from each other in size, shape, population, people, language, government, culture, and wealth. World maps are always changing, as new countries emerge from colonial rule or old ones divide or fall apart. Fifty years ago, there were only 82 independent nations, the rest being colonies or dependencies waiting to gain their independence.
Every part of Earth’s land surface belongs to or is claimed by one country or another, with the exception of Antarctica, where territorial claims have been set aside by international treaty (a formal agreement).
FACTFILE: POLITICAL WORLD
Largest country: Russian Federation 6,592,800 sq miles (17,075,400 sq km)
Smallest country: Vatican City 0.17 sq miles (0.44 sq km)
Longest border: US–Canada 5,526 miles (8,893 km)
Country with most neighbors: China (14), Russia (14)
Oldest country: Denmark, AD 950
Youngest country: East Timor, 2002
People have lived on Earth for two million years. For most of that time, the population has remained small, as the number of births has roughly equaled the number of deaths. Improved medicine and health care, better sanitation, improved farming methods producing more and better food, and less physical work have all led to fewer infant deaths and more people living longer. This has caused a massive increase in population over the last 150 years. Today, the world’s population is more than six billion and is rising at a rate of about one million a week.
The world’s six billion people are not evenly distributed around the planet, but concentrated in areas where the climate is suitable and the land habitable. This concentration of people is measured by population density, which is the average number of people living in each square mile.
HONG KONG, CHINA
Cities such as Hong Kong have solved the problem of limited space by building up rather than out. This has led to a growing number of so-called megacities, with populations of more than ten million. However, overcrowding, pollution, and a lack of open space make such cities unpleasant to live in.
Top five biggest cities and populations: Tokyo, Japan 34.9 million New York, NY 21.6 million Seoul, South Korea 21.1 million Mexico City, Mexico 20.7 million São Paulo, Brazil 20.2 million
Country with smallest population: Vatican City 900
Most densely populated country: Monaco 42,649 people per sq mile (16,404 people per sq km)
Least densely populated country: Mongolia 4 people per sq mile (2 people per sq km)
Country with highest birth rate: Niger 55 per 1,000 population
Country with lowest birth rate: Hong Kong/Macao (China) 7 per 1,000 population
Country with highest death rate: Sierra Leone 25 per 1,000 population
Country with lowest death rate: United Arab Emirates 2 per 1,000 population
Country with the highest life expectancy: Japan (81)
Country with the lowest life expectancy: Sierra Leone (39)
Richest country (highest GNP*): United States $9,602 billion
Poorest country (lowest GNP*): Tuvalu US$3 million
*GNP = Gross National Product
he rocky ball that forms our world is one of nine planets in the Solar System. Earth is a sphere, with a slight bulge in the middle at the Equator, and a diameter of 12,756 km (7,926 miles). It hurtles at speeds of 105,000 kph (65,000 mph) during its orbit around the Sun, turning on its AXIS once every 24 hours. This journey takes a year to complete. The Earth is the only planet that is known to support life, in a zone called the BIOSPHERE.
Water, oxygen, and energy from the Sun combine on Earth to help create suitable conditions for life. The planet’s surface is mainly liquid water, which is why it looks blue from space. Earth is the only planet in the Solar System with an atmosphere that contains a large amount of oxygen. The Sun is 150 million km (93 million miles) away, producing heat that is bearable on Earth.
The atmosphere is a layer of gas surrounding the Earth that is some 700 km (400 miles) thick. It is made up of nitrogen (78 per cent) and oxygen (21 per cent), plus traces of other gases. Tiny droplets of water vapour form the clouds we see.
Oceans cover 70.8 per cent of the Earth’s surface, to an average depth of 3.5 km (2 miles). The hydrosphere (watery zone) also includes freshwater rivers and lakes, but these make up less than 1 per cent of Earth’s water.
Dry land occupies 29.2 per cent of the Earth’s surface, where the lithosphere (rocky crust) rises above sea level to form seven continents and countless smaller islands. Land can be categorised into biomes – major habitats such as forests, grasslands, and deserts.
ICE AND SNOW
The cryosphere (frozen zone) includes snow and glaciers on high mountains, sea ice, and the huge ice caps that cover the landmasses of Greenland and the Antarctic. In the past, during long cold eras called ice ages, ice covered much more of Earth’s surface than it does today.
Meteorology, the study of Earth’s atmosphere, is one of the Earth sciences. Earth scientists study Earth’s physical characteristics, from raindrops to rivers and the rocks beneath our feet. Other branches of study include geology (rocks), hydrology, (oceans and freshwater), and ecology (living things and the environment).
Satellite images allow scientists to monitor everything from ocean currents to minerals hidden below ground. Techniques such as radar and sonar have transformed our understanding of our planet. Some Earth scientists also spend time in the field, which means working outdoors, collecting data and samples from clouds, cliffs, craters, volcanic lava, and deep-buried ice.
The biosphere is the part of Earth that contains what is needed for living things. This zone extends from the ocean floor to top of the troposphere (lower atmosphere). Tiny organisms can survive deep in the Earth’s crust, but most forms of life are found from a few hundred metres below sea level to about 1,000 m (3,300 ft) above sea level.
THE LIFE ZONE
Ozone is a gas spread thinly through the atmosphere. It filters harmful ultraviolet (UV) rays from sunlight, while allowing visible light (the light we can see) to pass through. Other gases in the atmosphere trap the Sun’s heat when it is reflected from the Earth’s surface, providing additional warmth for living things.
BIOGRAPHY: JAMES LOVELOCK British, 1919-
Environmental scientist James Lovelock argues that the planet can be seen as a complete living organism, which he names Gaia, after the Greek goddess of Earth. Gaia theory states that Earth itself balances conditions to suit living things in the biosphere. This includes regulating the composition of the atmosphere the chemistry of the oceans, and ground surface temperature.
The ground beneath our feet may seem still, but in fact the Earth is spinning like a top as it orbits the Sun. The Earth takes 24 hours to rotate about its axis, an imaginary line running from the North Pole to the South Pole through the centre of the Earth. The Earth’s axis is not at a right-angle to the path of its orbit, but tilts at an angle of 23.5°. The angle between each region of Earth and the Sun’s rays alters through the year, producing seasonal changes in temperature and day length. These are most noticeable in regions next to the poles, which are most distant from the Equator.
DAY AND NIGHT
As Earth turns about its axis, one half is bathed in sunlight and experiences day, while the other half is plunged into darkness and has night. The Earth always rotates eastward, so the Sun and stars appear to rise in the east and set in the west. The tilt of the planet means that at any time, one hemisphere (half of the Earth, as divided by the Equator) leans toward the Sun and experiences summer, while the other leans away and has winter.
The Earth is a giant, spinning ball of rock and metal. The rocky surface we live on is the Earth’s thin outer layer, called the crust. In places the crust is just a few kilometres thick. Underneath the crust are two more layers, called the mantle, and the core, which combine to reach a depth of 6,370 km (3,960 miles). Scientists discovered these layers by studying how shock waves from earthquakes change direction and speed as they travel through the Earth. It is thought that the core creates Earth’s MAGNETOSPHERE.
EARTH’S LIFE STORY
The Earth came into being about 4,600 million years ago. Along with the other planets and moons in our Solar System, it was made from material left over after the birth of the Sun. Earths surface has gone through many changes since, with the formation of the continents, oceans, and atmosphere, ’and the appearance of life.
Small particles of rock, dust, and gas in space are gradually pulled together by the gravity between them. The process is called accretion. The young Earth was formed by accretion over millions of years.
HEATING AND COOLING
Huge pressure in the centre of Earth created heat that melted the rocks inside. For hundreds of millions of years the surface was bombarded by meteorites from space. About 4,200 million years ago, Earth’s surface had cooled and a crust of solid rock had formed.
OCEANS AND ATMOSPHERE
The early atmosphere consisted of volcanic gases, which formed rain. From about 3,500 million years ago, this began to collect in oceans. Continents were also developing. Simple organisms in the oceans gave out oxygen into the atmosphere.
THE EARTH TODAY
An imaginary slice out of the Earth shows that scientists believe it has a core made mostly of solid and molten iron, a mantle of solid and half-molten rock, and a crust of solid rock. The inside of the Earth is still extremely hot. Plate tectonics, mountain building, and erosion are constantly changing the appearance of the Earth’s surface.
BIOGRAPHY: ANDRIJA MOHOVORICIC Croatian, 1857-1916
Geophysicist Andrija Mohorovicic found that earthquake shock waves sped up when they reached about 20 km (12 miles) below the surface. He suggested that happened at a boundary where two different layers of material met. This boundary is between the crust and the mantle, and is now known as the Mohorovicic discontinuity, or Moho.
The Earth has a magnetic field around it, and the magnetosphere is the region in which this field can be felt. It stretches more than 60,000 km (37,000 miles) into space, like an invisible magnetic bubble, and protects the Earth from harmful solar radiation. The solar wind, particles which stream from the Sun, pull the magnetosphere into a teardrop shape.
EARTH’S MAGNETIC FIELD
The Earth has a magnetic field that is the same shape as that of a bar magnet. It is as though the Earth contains a giant bar magnet with its poles located near the North Pole and South Pole. These magnetic Poles are tilted at a slight angle to the Earth’s axis. Scientists think that the magnetic field is caused by currents of molten metal in the Earth’s outer core. From time to time, these reverse, with north becoming south.
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Scientists believe that the Earth’s outer crust is made up of about huge fragments, called tectonic plates, that fit together like a cracked eggshell. According to the theory of plate tectonics, devised in the 1970s, these plates ride like rafts on the softer, red-hot rock below and very move slowly over the globe, carrying the continents with them. Past arrangements of tectonic plates created one vast SUPERCONTINENT.
Earth’s crust is a giant jigsaw of seven enormous plates and about twelve smaller ones. Many scientists believe plate movement is driven by slow-churning currents deep in the mantle beneath. As the plates drift, they converge (move towards each other) and collide, or grind past one another at transform margins, or diverge (pull apart).
The edges of the plates that make up the lithosphere are called boundaries or margins. New crust is mainly created at plate boundaries in mid-ocean, where the SEA-FLOOR IS SPREADING. Older crust is destroyed near the edges of oceans, where plates collide and one subducts (dives) below the other and melts. This causes the plates to move very slowly over the softer asthenosphere, below.
The shapes of continents such as eastern South America and western Africa would fit neatly if pushed together. The discovery of matching fossils and rock layers on land separated by wide oceans provided further evidence that landmasses were once united. Scientists call this supercontinent Pangaea. The slow movement of Earth’s plates caused Pangaea to split apart.
Some 300 million years ago, plate movement drove Earth’s landmasses together to form Pangaea (All-Earth). This was surrounded by the vast ocean Panthalassa. About 100 million years later Pangaea began to break up.
An arm of the Tethys Sea, an ancient ocean, opened to split Pangaea in two. To the north lay Europe, North America, Greenland, and Asia, with South America, Africa, India, Australia, and Antarctica to the south.
As plate movement continued, these large fragments split into smaller continents, which slowly came to their present positions. They continue to move at a rate of a few centimetres per year.
BIOGRAPHY: ALFRED WEGENER German, 1880-1930
Climate expert and geophysicist Alfred Wegener pioneered the theory of continental drift in 1915. He became convinced that the continents were once joined, and put forward the idea of Pangaea. On the Arctic island of Spitzbergen, Wegener found fossils of tropical ferns, which suggested that the island had once lain in the tropics. His ideas were not taken seriously until the 1960s.
Mountain chains, longer and mightier than any on land, run down the centre of the oceans. At these mid-ocean ridges, where tectonic plates diverge, molten magma erupts to bridge the gap. Rock samples taken from the Atlantic floor in the 1960s showed that the youngest rocks lay in the centre of the ridges, with older rocks to either side. As the new rock forms, older rock is pushed aside, and the sea floor widens, or spreads.
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Earthquakes are caused by movements of the giant tectonic plates that form Earth’s crust. SEISMOLOGY is the study of earthquakes. Most occur at cracks called FAULTS, at the boundaries where the plates meet. Every minute, the ground shakes somewhere in the world, but these vibrations are usually minor tremors that are barely noticed. When a major earthquake strikes, the ground shakes violently, and buildings and bridges topple.
As the plates slowly shift, rocks are put under pressure. They stick, then stretch and, as the strain gets too great, they shatter and jolt into new positions. Seismic (shock) waves radiate from the earthquake’s focus, underground. The epicentre, above the focus, suffers the worst damage.
Faults are deep cracks in rocks, mostly caused by movement at plate margins. Deep earthquakes strike in subduction zones where two plates collide and one slides below the other. Shallow earthquakes occur mostly where two plates grind past one another. The rocks may be shifted only a few centimetres, but over millions of years, this can add up to hundreds of kilometres of movement sideways, and up to 30 km (19 miles) of vertical movement.
NORMAL DIP-SLIP FAULT
The rocks along a fault may move up or down, sideways or diagonally, depending on the angle of the fault plane. The angle of the fault plane to the horizontal is known as the dip. In a normal fault, also known as a dip-slip fault, the rocks shift straight down or up, following the line of dip.
The distance that the rocks slip up or down during a quake or tremor is called the throw. In a reverse fault, pressure causes one block of rock to overhang another. As the rocks shift, the block is forced farther up and over the other. A reverse fault with a fault plane of 45° or less is called a thrust fault.
In a strike-slip fault, rocks scrape sideways past one another. The amount of sideways slip is called the heave. The San Andreas Fault, which runs along the west coast of North America, is a famous example. The rocks in an oblique-slip fault slide past each other, and also up and down in a diagonal movement.
Seismologists study earthquakes. They also examine the behaviour of seismic waves passing through the Earth to find out about its structure. Instruments called seismographs measure the intensity of seismic waves. The magnitude (size) of earthquakes can be rated by measuring either these waves, on the Richter scale, or the damage caused – the Mercalli scale. Earthquakes cannot be prevented, but they can sometimes be accurately predicted.
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Volcanoes are vents (openings) in the ground from which magma (molten rock), ash, gas, and rock fragments surge upwards, in an event called an eruption. They are often found at boundaries between the plates in Earth’s crust. Volcanic eruptions produce volcanoes of different shapes, depending on the type of eruption and the region’s geology. HYDROTHERMAL ACTIVITY occurs where underground water is heated by rising magma.
Magma that flows over the Earth’s surface is called lava. A shield volcano produces lava that spreads over a wide area to form a broad mound. Magma collects underground in a space called a magma chamber, before erupting through vents to form low cones, and through fissures (long cracks).
A dome, or cone, volcano is formed when thick, sticky lava erupts from a volcano crater. The lava cools and solidifies quickly to form a dome. Further eruptions may add more layers. The collapse of a dome can produce dangerous pyroclastic flows – fast-moving flows of hot gas and volcanic fragments.
A steep-sided composite volcano is made of alternating layers of ash and lava, produced by a series of eruptions. Its thick magma does not flow far before solidifying. This type of volcano often has a main vent, fed by a chimney rising from its magma chamber, and additional side vents.
Magma forms when the rocks below the Earth’s crust melt. A flow of erupted magma along the Earth’s surface is called lava. When red-hot lava flowing from volcanoes cools, it solidifies into many different forms. One, pahoehoe lava, is fast-flowing and runny. As it cools, it forms a smooth, shiny skin, under which lava continues to flow. This sometimes wrinkles the smooth surface into ropelike coils.
Unlike smooth-skinned pahoehoe lava, aa lava has a rough surface, which is difficult to walk on and sharp enough to rip rubber shoes. This jagged material is formed when slow-moving, sticky lava cools and breaks up into sharp, blocky shapes. Flows of aa lava can be thick, reaching heights of up to 100 m (330 ft). The words for aa (pronounced ah-ah) and pahoehoe (pahow-ee-how-ee) lava come from Hawaii, where these lava types occur and were first studied.
The word “hydrothermal” comes from the Greek words for water and heat. In volcanic regions, the combination of heat and water below ground produces remarkable effects. In the oceans, openings called hydrothermal vents form when cracks containing red-hot magma fill with seawater. They spout black clouds of hot water mixed with gas and minerals. Hydrothermal activity on land produces hot springs, geyser, and pools of bubbling mud.
New mountains are built when rocks are pushed upwards by the movement of the giant rocky plates that make up the Earth’s crust. The rocks are pushed upwards in two ways: FOLD mountains are formed when layers of rock become buckled, and BLOCK mountains are formed when giant lumps of rock rise or fall. Volcanic eruptions also create mountains. Many mountain ranges have been built up and eroded away since the Earth was formed.
The Andes is the longest mountain range on land. It was formed along the western margin of South America, where two tectonic plates (rocky plates that make up the Earth’s crust) collided. The mountains are still rising by about 10 cm (4 in) every century.
Fold mountains are pushed up at a boundary where two tectonic plates collide. The boundary between an ocean plate and a continental plate is called a subduction zone. Here, the thin ocean crust slides slowly under a thicker continental crust, making the rocks buckle and fold. The ocean plate also melts, creating magma (molten rock) that rises to form volcanoes.
WORLD MOUNTAIN RANGES
The world’s major mountain ranges, such as the Andes, the Himalayas, and the Alps, are situated along the boundaries where tectonic plates collide. These ranges formed in the last few hundred million years, so are they quite young. The map also shows thin lines of volcanoes that erupt from the ocean floor, forming chains of mountainous islands.
The Himalayas is a range of fold mountains formed by the collision between India and the rest of Asia. When the two tectonic plates collided, the southern edge of Asia buckled. The Indian plate continues to slide under Asia and, to date, has uplifted Tibet to a height of over 5 km (3 miles).
When layers of rock are pushed inwards from both ends, they crumple up into waves called folds. Rocks are too hard to be squashed into a smaller space. Instead they fold upwards and downwards. The immense forces that cause folding can crunch solid rocks into folds just a few metres across.
The rocks that buckle to form fold mountains are made up of layers of sedimentary rocks and igneous rocks. When the layers are folded, the rocks on the outside of a fold are stretched and the rocks on the inside of a fold are squashed. The folding also makes the layers of rock slide over each other.
Block mountains are mountains formed when layers of rock crack into giant blocks. Cracks in layers of rock are called faults. They form when the Earth’s crust is stretched, squashed, or twisted. The blocks are free to slip up, down, or sideways, or to tip over. These movements are very slow, but over millions of years they form mountains thousands of metres high.
THE FOSSIL RECORD
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Geologists (scientists who study rocks) divide the time since the Earth was formed until today into chunks called periods. During the various periods, different species of animals and plants lived on the Earth. For example, the Cretaceous period, which lasted from 146 million years ago to 65 million years ago, was the final period of the dinosaurs. Some rocks can be given a relative age by identifying the fossils they contain. The date of formation of some rocks can be found by using RADIOMETRIC DATING.
Coastal features, such as cliffs and arches, are formed by wave erosion. As the sea beats on rocky headlands, softer rocks are eroded (worn away) to form hollow caves. Twin caves on either side of a headland may eventually wear right through to form an arch. As the battering continues, the top of the arch collapses to leave an isolated pillar.
In the last few million years, sea levels have risen and fallen by up to 200 m (660 ft). Scientists believe these are caused by temperature changes, as Ice Ages come and go. During Ice Ages, sea levels are low because large amounts of water are frozen. When the climate warms, the ice melts and sea levels rise. Today, sea levels look set to rise because of global warming. This will bring a risk of flooding to coasts.
During an Ice Age, the weight of the ice depresses (pushes down) the land. Sea levels are low, so the crust beneath the ocean is not depressed. When the weather warms, melting ice causes sea levels to rise. This effect is partly offset by the land springing up when released from the ice’s weight, while the ocean bed sinks beneath the weight of water.
The water in the oceans is never still, but moves continually in strong currents that flow both near the surface and at great depths. This helps to distribute the Sun’s heat around the globe. Winds create surface currents, which are then bent by Earth’s rotation and by land masses to flow in great circles, called gyres. Warm surface currents coming from the tropics warm the lands they flow past. Cool deep currents flowing from polar waters have the opposite effect.
ust a century ago, the ocean floor was largely unknown. Now we know that the deep oceans have features such as mountains, deep valleys, and vast plains. Many of these are formed by the movement of the tectonic plates that make up Earth’s crust. Far below the ocean’s surface, volcanic mountain chains are rising in mid-ocean zones where plates pull apart. Elsewhere, deep trenches descend in subduction zones where plates collide and one dives below the other.
Oceanographers use sonar to map the ocean floor. The research ship directs sound waves at the bottom, and charts the echoes that bounce back to create a detailed map. Sonar has revealed features such as seamounts (submerged volcanic peaks), which rise 1,000 m (3,300 ft) from the sea floor, and guyots (flat-topped seamounts).
In 1977, scientists used submersible vehicles to explore the seabed and discovered vents gushing dark plumes of superhot, mineral-rich water. These black smokers, are caused by volcanic activity at mid-ocean ridges. Water entering cracks in the crust is heated by magma and mixed with mineral sulphides, then belched forth in dark clouds.
Islands are land masses entirely surrounded by water. They are found in oceans, seas, rivers, and lakes. Islands vary in size from tiny rock outcrops to vast areas such as Greenland, which covers 2.2 million sq km (840,000 sq miles). There are two main types of island: oceanic islands which are remote from land; and continental islands, which often lie close to the mainland. Many oceanic islands are volcanoes. Continental islands are often formed by changes in sea level.
Continental islands, such as the British Isles, rise from the shallow waters of continental shelves, which fringe the world’s continents. Often these islands were once part of the mainland, but were cut off when sea levels rose to flood the land in between. Smaller islands, called barrier islands, sometimes form off coasts where ocean currents or rivers deposit sand or mud.
Coral islands, such as the Maldives in the Indian Ocean, are composed of the limey skeletons of coral polyps. Large colonies of these anemone-like creatures thrive in the warm, shallow waters off tropical coasts or around seamounts. The polyps’ soft bodies are protected by cup-shaped shells, which grow on top of one another to form rocky reefs that eventually break the surface. If the seamount subsides, just a ring of coral, called an atoll, may be left.
ISLAND CHAINS AND HOT SPOTS
Chains of volcanic islands sometimes form near the centre of tectonic plates, in zones called hot spots. Some scientists believe that hot spots occur where magma plumes surge up from the mantle below. The magma bursts through a weak point in the crust to form an island. Over millions of years, the hot spot stays in the same place as the crustal plate drifts over it, forming new islands.
Oceanic islands are often formed by volcanic eruptions when plates collide. As one plate is forced below another, its crust melts in the red-hot mantle below. This molten rock rises up again to burn through the crust and erupt on the sea floor. Over time, the erupted rock forms a tall seamount and eventually breaks the surface as an island.
When water flows over some rocks, such as limestone, caves may be formed by a process called chemical weathering. Water seeps into cracks and gradually dissolves the rock, widening the cracks until, over thousands of years, the limestone becomes riddled with caves and passageways. Water flowing through caves forms underground streams, rivers, and pools (such as this one in Mexico). Surface rivers disappear into sink holes and reappear many kilometres away. Eventually a cave roof may fall in, creating a gorge.
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Groundwater is water under the Earth’s surface. Most groundwater is found in porous rocks, which have tiny holes in them. If a hole is bored straight down through the rock, groundwater is eventually found at a certain level. This level is called the water table, and it usually rises when rainwater soaks into the ground. A spring is a place where groundwater emerges from a hillside.
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Lakes form where water fills hollows in the landscape. Some of these hollows are formed by glaciers gouging into the ground, and some are created when river valleys are blocked by dams. Other lakes are formed in volcanic craters, or when land sinks during earth movements. Most lakes contain freshwater, but there are some saltwater lakes, such as the Dead Sea between Israel and Jordan.
Auroras are shimmering curtains of light seen at night in the polar regions. They are known as the Northern Lights in the Arctic, and as the Southern Lights in the Antarctic. These spectacular displays are caused by charged particles from the Sun striking the upper atmosphere above the poles.
Ozone is a form of oxygen that gathers in the stratosphere to form a layer. This layer screens out harmful ultraviolet (UV) rays from the Sun, which can cause skin cancer. In the 1980s, scientists discovered that thin areas, or holes, were appearing in the ozone layer over the polar regions each spring. Ozone loss is caused by chemicals called chlorofluorocarbons (CFCs).
Earth’s landmasses can be divided into nine major climate zones, based on their usual temperature, rainfall, and the type of vegetation that grows there. Tropical areas are hot all year round, while polar regions and the tops of high mountains are always cold. Temperate zones in between the poles and the tropics, such as temperate forests and Mediterranean regions, have moderate, but seasonally changing, climates. Deserts are dry, receiving less than 25 cm (9 in) of rainfall every year.
A flash of lightning is a giant spark of electricity. When ice crystals and water droplets move about and collide inside a thundercloud, static electricity builds up. Lightning is set off when the spark jumps through a cloud, or from one cloud to another, or from a cloud to the ground. A bolt of lightning heats the air to about 30,000°C (54,000°F) so the air expands suddenly and causes a clap of thunder.
HOW LIGHTNING STRIKES
Negative electric charge builds up in the base of a thundercloud, and positive charge in the top. The negative and positive charges are attracted to each other, so lightning can strike through the cloud. The negative charge in the cloud’s base also attracts positive charges in the ground, so eventually a lightning spark leaps through the air between the cloud and the ground.
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The Earth has many natural resources that make life in the modern world possible. For example, rocks are used in their natural state to make buildings, but they can also be processed to provide the materials we need to make anything from bridges and cars to silicon chips and jewellery. FOSSIL FUELS provide us with energy, but so does water flowing down rivers, the wind, and even the Sun. Resources such as rocks and fossil fuels must often be extracted from the ground by MINING.
Rocks contain a great variety of useful minerals. Mining and quarrying involve blasting, drilling, and digging up rocks to extract the minerals. Most mines and quarries are worked for building materials, coal, metal ores, and gem-rich rocks and deposits. Mining is noisy, dusty, and can require the use of dangerous chemicals, all of which can cause environmental damage.
A gold mine in Indonesia is an example of an underground mine, where rock is dug out by machinery deep under the surface. There are two main types of underground mine: shaft mines, which are normally deep, with vertical shafts leading to tunnels; and drift mines, which are near the surface. Underground mining is very dangerous because of possible flooding, explosive gases, and falling rocks.
At the Bingham copper mine in Utah, USA, the ore deposit is close to the surface and is extracted by opencast mining. Opencast mining is cheaper and easier than underground mining because no shafts have to be dug, but it does more damage to the landscape. Once the ore is dug up, it is carried away by trucks, railway, or conveyor belts.
Coal, oil, and gas are called fossil fuels because they were formed from the remains of animals and plants that were buried by layers of sediment millions of years ago. Most of the energy used today comes from burning fossil fuels. Fossil fuels are non-renewable sources of energy, which means that once they have been used they can never be replaced.
OIL AND GAS
Many of the world’s oil and gas supplies are found in rock under the sea, from where they are extracted through pipes drilled into the seabed from production platforms. Where oil and gas are found together, they were formed from the bodies of microscopic marine organisms. Oil is a source of chemicals as well as fuel.
Coal is formed by the burial of plant remains before they rot completely. Surface deposits of vegetation form layers of peat that become lignite and coal as they are more deeply buried over time. Burial compresses the plant remains and squeezes out any water. Further pressure turns coal into anthracite.
The seven oceans: North Pacific, South Pacific, North Atlantic, South Atlantic, Indian Ocean, Southern Sea, Arctic Ocean
The seven continents: North America, South America, Europe, Africa, Asia, Australia/Oceania
The three North American time zones:
Note that students should also learn how to read a map and compass; how to identify the four directions; and how to draw or make a model of the earth, the solar system and the path of the earth around the sun and the moon around the earth, showing how they rotate and how those rotations and shadows create days, nights and years. They should also learn about their local natural area, including their own time zone, climate type and seasonal changes as well as the names of common local rocks, trees, flowers, insects and other animals.
Basic Meteorology Knowledge Checklist
Weather: The atmospheric conditions caused by changing air pressure and heat from sun
Climate: The long-term weather conditions of a particular area
Wind: The movement of air that happens when higher pressure air is moving toward lower pressure air. If there’s no pressure difference, there is no wind.
Storm: Any disruption in the atmosphere producing severe weather, including strong wind, tornadoes, hail, rain, snow (blizzard), lightning (thunderstorm), clouds of dust or sand carried by wind (a dust or sand storm)
Lightning: The visible and audible flow of electricity that occurs during a thunderstorm. It can occur inside a single cloud, between clouds, or between a cloud and the ground. It produces an audible booming sound called thunder. Since the speed of light is greater than the speed of sound, we hear thunder after we see lightning.
Tornado: A funnel-shaped column of wind, evaporated water, dust and debris that moves rapidly, sweeping up objects in its path. It is formed when a thunderstorm occurs in areas of both cold and warm air.
Hurricane/typhoon/tropical cyclone/tropical storm: A spiral-shaped group of thunderstorms formed over the ocean that forms a cyclone (a circular movement of wind with a low-pressure center)
Earthquake: A sudden shaking of the surface of the earth due to shifts in tectonic
Seismic activity: The sum of all of the tremors and earthquakes in a region
Tsunami: A series of huge, destructive waves formed due to major events like hurricanes, volcanic eruptions, meteorite crashes and earthquakes. Tsunamis are sometimes mistakenly known by the misnomer tidal wave.
Evaporation: Water vapor that is breaking free from the rest of the liquid
Condensation: The water vapor that collects back into drops on a solid. It comes from the air.
Water vapor: The gas that forms when water evaporates
Dew: The water vapor that forms as the sun rises and begins to warm cold air and humidity into condensation
Humidity: The water vapor in the air
Atmospheric particle/particulate: Microscopic solid or liquid particles suspended in the atmosphere. Some are organic and others are human-made.
Thermometer: A tool to measure temperature
Barometer: A tool to measure air pressure
Main climate types: Tropical (Wet/rain forest, Monsoon, and Wet and Dry/Savanna); Dry (Arid and Semiarid); Mild (Mediterranean, Humid subtropical and Marine); Continental (Warm summer, Cool summer and Subarctic/Boreal); and Polar (Tundra and Ice cap).
How to make a sundial: Draw a simple clock face. Suspend a stick or pencil in the center of it. Sit in face up in the sun in a way in which the stick’s shadow points to the appropriate time.
Read the rest of this series at Knowledge Checklists: Filling My Educational Gaps, One Subject at a Time.
And peruse my full recommended reading list at Books I Want My Kids to Read Someday.