- Earth is the third planet from the sun and the fifth largest in the solar system.
- Earth is 92,955,820 miles (149,597,891 kilometers) away from the sun.
- At 7,917.5 miles (12,742 kilometers), Earth’s diameter is just a few hundred kilometres larger than that of Venus.
- The four seasons are a result of Earth’s axis of rotation being tilted more than 23 degrees.
- The length of a year on Earth is 365 days, 6 hours, and 16 minutes.
- The length of the day on Earth is 23 hours and 56 minutes.
Shape of the Earth
- Sphere – Earth’s radius is around 6,371 kilometers, is considered to be one of the characteristic of perfect spheres.
- Oblate Spheroid or Oblate Ellipsoid – where poles are flattened and equator bulges, is an ellipsoid of revolution obtained by rotating an ellipse about its shorter axis.
- Geoid – coincides with that surface to which the oceans would conform over the entire earth if free to adjust to the combined effect of the Earth’s mass attraction and the centrifugal force of the Earth’s rotation.
Internal Structure of the Earth
- Inner core – hottest part of the Earth. It is solid and made up of iron and nickel with temperatures of up to 5,500 C.
- Outer core – the layer surrounding the inner core. It is a liquid layer, also made up or iron and nickel.
- Mantle – widest section of the Earth. It has a thickness of approximately 2,900 kilometers. The mantle is made up of semi-molten rock called magma.
- Crust – the outer layer of the Earth. It is a thin layer between 0 – 60 kilometers thick.
- Oceanic Crust – around 3-4 miles thin (5-7 km) and made up of basalt.
- Continental Crust – stretches around 20-30 miles thin (30 – 50 km) and made of granite.
Continental Drift Theory
- Urkontinent – Alfred Wegener’s original name for his proposed, ancient continent was “Urkontinent”—urmeaning “first or original,” and continent meaning “continent” in Wegener’s native language, German. A more popular name for this huge ancient landmass is Pangaea, which means “all lands” in Greek.
- The theory of continental drift is most associated with the scientist Alfred Wegener. In the early 20th century, Wegener published a paper explaining his theory that the continental landmasses were “drifting” across the Earth, sometimes plowing through oceans and into each other. He called this movement continental drift.
- Pangaea – Wegener was convinced that all of Earth’s continents were once part of an enormous, single landmass called Pangaea.
- Evidences : (a) Wegener, trained as an astronomer, used biology, botany, and geology describe Pangaea and continental drift. For example, fossils of the ancient reptile mesosaurus are only found in southern Africa and South America. Mesosaurus, a freshwater reptile only one meter (3.3 feet) long, could not have swum the Atlantic Ocean. The presence of mesosaurus suggests a single habitat with many lakes and rivers. (b) Wegener also studied plant fossils from the frigid Arctic archipelago of Svalbard, Norway. These plants were not the hardy specimens adapted to survive in the Arctic climate. These fossils were of tropical plants, which are adapted to a much warmer, more humid environment. The presence of these fossils suggests Svalbard once had a tropical climate. (c) Finally, Wegener studied the stratigraphy of different rocks and mountain ranges. The east coast of South America and the west coast of Africa seem to fit together like pieces of a jigsaw puzzle, and Wegener discovered their rock layers “fit” just as clearly. South America and Africa were not the only continents with similar geology. Wegener discovered that the Appalachian Mountains of the eastern United States, for instance, were geologically related to the Caledonian Mountains of Scotland.
- Today, scientists think that several supercontinents like Pangaea have formed and broken up over the course of the Earth’s lifespan. These include Pannotia, which formed about 600 million years ago, and Rodinia, which existed more than a billion years ago.
Seafloor Spreading Hypothesis
- Seafloor spreading is a geologic process in which tectonic plates—large slabs of Earth’s lithosphere—split apart from each other.
- Seafloor spreading and other tectonic activity processes are the result of mantle convection. Mantle convection is the slow, churning motion of Earth’s mantle. Convection currents carry heat from the lower mantle and core to the lithosphere. Convection currents also “recycle” lithospheric materials back to the mantle.
- Seafloor spreading occurs at divergent plate boundaries. As tectonic plates slowly move away from each other, heat from the mantle’s convection currents makes the crust more plastic and less dense. The less-dense material rises, often forming a mountain or elevated area of the seafloor.
- Seafloor spreading occurs along mid-ocean ridges—large mountain ranges rising from the ocean floor. The Mid-Atlantic Ridge, for instance, separates the North American plate from the Eurasian plate, and the South American plate from the African plate. The East Pacific Rise is a mid-ocean ridge that runs through the eastern Pacific Ocean and separates the Pacific plate from the North American plate, the Cocos plate, the Nazca plate, and the Antarctic plate. The Southeast Indian Ridge marks where the southern Indo-Australian plate forms a divergent boundary with the Antarctic plate.
- The Mid-Atlantic Ridge, for instance, is a slow spreading center. It spreads 2-5 centimeters (.8-2 inches) every year and forms an ocean trench about the size of the Grand Canyon.
- The East Pacific Rise, on the other hand, is a fast spreading center. It spreads about 6-16 centimeters (3-6 inches) every year. There is not an ocean trench at the East Pacific Rise, because the seafloor spreading is too rapid for one to develop!
Plate Tectonic Theory
- Plate tectonics is the theory that explains the global distribution of geological phenomena. Principally it refers to the movement and interaction of the earth’s lithosphere. This includes the formation, movement, collision and destruction of plates and the resulting geological events such as seismicity, volcanism, continental drift, and mountain building.
- Plate Boundaries or plate margins describe the fault zones separating two distinct plates. There a three main types of plate boundary, namely, convergent, divergent and transform or conservative. Covergent plate boundaries describe two plates that are moving into each other. There are three types of convergent plate boundary. One, destructive oceanic-continental boundaries, where the younger and less dense oceanic crust is subducted under the older lighter continental crust. Two, the destructive oceanic-oceanic boundary where one oceanic plate is subducted under another oceanic plate. These boundaies form oceanic island arcs like that of the Philippines. Three, collision boundaries where a continental plate collides with a second continental plate. At this plate boundary great fold mountains develop. The Himalayas were formed in this way as India crashed into Eurasia around 50 million years ago. Divergent plate boundaries form when plates are moving apart. Examples of divergent plate boundaries are constructive margins like those found at mid-oceanic ridges as well as continental rift valleys. The final type of plate boundary is a transform boundary. Transform boundaries form as plates move alongside each other and in doing so create shear stress. These margins are associated with frequent earthquakes like those that occur at the San Andreas Fault.
- Divergent Plate Boundary (Continental Rift Valleys) – Active continental rift valleys can be found in two places, the East African Rift Valley and the Baikal Rift Zone in south eastern Russia. At these margins continental crust is being pulled apart. As tensional stresses stretch the crust, the brittle upper crust becomes faulted. Horsts are areas of raised land and grabens are lowered areas that form between two faults. Rift valleys are characterised by a combination of normal and reverse fault zones. The rifting reduces the pressure on the asthenosphere which in turn causes some melting. Magma then rises to the surface of the rift creating volcanoes. If this processes continues long enough the two continental plates may break completely apart and separate fresh ocean crust begins to form.
- Convergent Plate Boundary (Destructive, Oceanic-Continental) – At Oceanic-continental destructive margins continental island arcs form and at these margins that we find many of the world’s most violent volcanoes. The ‘Pacific Ring of Fire’ is dominated by destructive margins where young dense oceanic crust is forced to subduct beneath the older and more buoyant continental plate. The Andes mountain have been formed as the Nazca Plate is subducted beneath the South American Plate.
- Destructive margins are characterised by a number of distinctive features. Namely deep ocean trenches and accretionary wedges and marginal geosynclines. In addition, mountain chains develop which are punctuated by active volcanoes. As the oceanic crust and surrounding lithosphere is subducted under the continental plate a deep sea ocean trench forms. You can observe in the animation how the trench moves over time due to the deposition of sediments from the subducted plate. These sediments grow in size and can become metmorphosed due to compressional stress and form a geosyncline. Whilst accretionary wedges are more dynamic, geosynclines are more permanent geolgical structures. At approximately 100 kilometers of depth the mantle wedge above the subducting plate begins to melt as a result of the release of water. Water reduces the density of the asthenosphere, which in turn lowers the melting point and causes magma to form. This molten magma then rises up into the lithosphere to form intrusive magma chambers and on the surface volcanoes. This type of margin is also characterised by a deep active seimic area called the Benioff zone. This zone produces deep-seated earthquakes, where the foci can reach depths as low as 700 kilometers.
- Divergent Plate Boundary (Collision) – At most continental-continental collision zones like that found at the boundary between the Indo-Australian Plate and the Eurasion Plate the collision of continental crust has been proceeded by the subduction of oceanic crust. In the case of the Himalayan Mountain range the Tethys Sea vanished as its underlying crust was compressed and subducted beneath Eurasia between 40 and 50 million years ago. The Indian continent that followed was too buoyant to be subducted and crashed into Eurasia with tremendous compressional force. The resulting landforms are flanks of great fold mountains that rise to their peak at over 9000 meters. Interestingly at the top one finds the sedimentary rocks that once formed the ocean floor of the Tethys. All continental collision zones are characterised by great fold-thrust mountain belts. These pressures also create a deep seated lithosphere called a mountain root. It is possible for the mountain root to break away from the lithosphere.
The Rock Cycle
Three main types of rock;
- Sedimentary, for example, chalk, limestone, sandstone and shale.
- Igneous, for example, basalt and granite.
- Metamorphic, for example slate and marble.
- Continual Change – The Earth’s rocks do not stay the same forever. They are continually changing because of processes such as weathering and large earth movements. The rocks are gradually recycled over millions of years. This is called the rock cycle.
- Sedimentation creates layers or rock particles.
- Compaction and cementation presses the layers and sticks that particles together. This creates sedimentary rock.
- Rocks underground that get heated and put under pressure are changed into metamorphic rock.
- Rocks underground that get heated so much they will melt turn into magma. Magma is liquid rock. Magma also comes from deeper inside the Earth, from a region called the mantle.
- Pressure can force magma out of the ground. This creates a volcano. When the magma cools it turns into solid rock, called extrusive igneous rock.
- Magma that cools underground forms solid rock called intrusive igneous rock.
- Areas of rock can move slowly upwards, pushed up by the pressure of the rocks forming underneath. This is called uplift.
- Weathering breaks down rocks on the surface of the Earth. There are three types of weathering – physical, chemical, and biological.
- Wind and water move the broken rock particles away. This is called erosion.
- Rivers and streams transport rock particles to other places.
- Rock particles are deposited in lakes and seas, where they build up to form layers. This starts the process of sedimentation which will create sedimentary rock.
Minerals and Rocks
- Rocks are made of grains that fit together. Each grain in the rock is made from a mineral, which is a chemical compound. The grains in a rock can be different colours, shapes, and sizes.
- Minerals are naturally occurring solid compounds. These are the requirements that it must met according to geologists: (a) naturally occurring, (b) inorganic, (c) solid, (d) definite chemical composition, (e) ordered internal structure.
- Determining Properties of the Minerals.
- Luster describes the appearance of a mineral when light is reflected from its surface. (eg: metallic luster, earthy luster, vitreous luster, waxy luster)
- Color is one of the most obvious properties of a mineral but it is often of limited diagnostic value, especially in minerals that are not opaque.
- Streak refers to the color of the mineral in its powdered form, which may or may not be the same color as the mineral.
- Hardness is the resistance of a mineral scratching or abrasion by other materials. The standard hardness scale, called Mohs Hardness Scale, consists of ten minerals ranked in ascending order of hardness with diamond, as the hardest known substance.
- A mineral that exhibits cleavage consistently breaks, or cleaves, along parallel flat surfaces called cleavage planes. A mineral fractures if it breaks along random, irregular surfaces.
- Crystal Form – a crystal is a solid, homogenous, orderly array of atoms and may be nearly any size. The arrangement of atoms within a mineral determines the external shape of its crystals.
- Additional properties include magnetism, reaction with acid, striations, specific gravity, and taste, odor, feel.
- Refer to this site for the list of existing minerals and their uses: http://geology.com/minerals/.
- Weathering – is the breakdown of rocks at the Earth’s surface, by the action of rainwater, extremes of temperature, and biological activity. It does not involve the removal of rock material. Weathering involves no moving agent of transport. Three types of weathering, physical, chemical, and biological.
- Erosion – is the process by which soil and rock particles are worn away and moved elsewhere by wind, water or ice.
- Lithification – the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. It is a process of porosity destruction through compaction and cementation.
- Sedimentation – the tendency for particles in suspension to settle out of the fluid in which they are entrained and come to rest against a barrier. In geology, sedimentation is often used as the opposite of erosion, the terminal end of sediment transport.
- Saltation is a specific type of particle transport by fluids such as wind or water. It occurs when loose material is removed from a bed and carried by the fluid, before being transported back to the surface.
- Orogeny – an event that leads to a large structural deformation of the Earth’s lithosphere (crust and uppermost mantle) due to the interaction between tectonic plates.
- Liquefaction – Soil liquefaction describes a phenomenon whereby a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid.
- Geologic Folding is a type of Earth movement resulting from the compression of rocks strata (or rock layers). Bending, curving, crumpling, or bucking of rocks into folds is usually visible on rock strata.
- Geologic Faulting is another type of Earth movement that forms cracks or fractures in rocks. These cracks are called fault lines.
- Ocean Basin Formation – Ocean basins are formed from series of processes beginning with a separation of two diverging plates where molten rock materials well up from the underlying mantle into the ridge or the gap between the diverging plates, solidifying into an oceanic crust.
The Water Cycle – Earth’s water is always in movement, and the natural water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth.
- Evaporation is the process by which water changes from a liquid to a gas or vapor. It is the primary pathway that water moves from the liquid state back into the water cycle as atmospheric water vapor.
- Condensation is the process by which water vapor in the air is changed into liquid water. It is crucial to the water cycle because it is responsible for the formation of clouds. It is responsible for ground-level fog, for your glasses fogging up when you go from a cold room to the outdoors on a hot, humid day.
- Precipitation is water released from clouds in the form of rain, freezing rain, sleet, snow, or hail.
- Sublimation is the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage. Sublimation occurs more readily when certain weather conditions are present, such as low relative humidity and dry winds.
- Inflitration – anywhere in the world, a portion of the water that falls as rain and snow inflitrates into the subsurface soil and rock. How much infiltrates depends greatly on a number of factors (precipitation, base flow, soil characteristics, soil saturation, land cover, slope of land, evapotransportation).
- Tidal currents occur in conjunction with the rise and fall of the tide. When a tidal current moves toward the land and away from the sea, it “floods.” When it moves toward the sea away from the land, it “ebbs.”
- Tidal currents are the only type of current affected by the interactions of the Earth, sun, and moon.
- Tidal currents, just like tides, are affected by the different phases of the moon. When the moon is at full or new phases, tidal current velocities are strong and are called “spring currents.”
- When the moon is at first or third quarter phases, tidal current velocities are weak and are called “neap currents.”
- When the moon and Earth are positioned nearest to each other, the currents are stronger than average and are called “perigean currents.”
- When the moon and Earth are at their farthest distance from each other, the currents are weaker and are called “apogean currents.”
- Coastal Currents are intricately tied to winds, waves, and land formations. Wave height is affected by wind speed, wind duration (or how long the wind blows), and fetch, which is the distance over water that the wind blows in a single direction.
- Longshore currents are generated when a “train” of waves reach the coastline and release bursts of energy. When a wave reaches a beach or coastline, it releases a burst of energy that generates a current, which runs parallel to the shoreline.
- As longshore currents move on and off the beach, “rip currents” may form around low spots or breaks in sandbars, and also near structures such as jetties and piers. A rip current, sometimes incorrectly called a rip tide, is a localized current that flows away from the shoreline toward the ocean, perpendicular or at an acute angle to the shoreline.
- Winds blowing across the ocean surface often push water away from an area, When this occurs, water rises up from beneath the surface to replace the diverging surface water. This process is known as “upwelling.”
- Because the Earth rotates on its own axis, circulating air is deflected toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere, resulting in curved paths. This deflection is called the Coriolis Effect.
- The Ekman Spiral is a consequence of the Coriolis Effect. Like the surface water, however, the deeper water is deflected by the Coriolis Effect – to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. As a result, each successively deeper layer of water moves more slowly to the right or left, creating a spiral effect.
- Global winds drag on the water’s surface, causing it to move and build up in the direction that the wind is blowing. And just as the Coriolis effect deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, it also results in the deflection of major surface ocean currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
- These major spirals of ocean-circling currents are called “gyres” and occur north and south of the equator. They do not occur at the equator, where the Coriolis effect is not present.
- There are five major ocean-wide gyres – The North Atlantic, South Atlantic, North Pacific, South Pacific, and Indian Ocean gyres.
Fresh Water and Salt Water
- Fresh water is naturally occurring water on Earth’s surface in ice sheets, ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers, and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved slats and other total dissolved solids.
- Salt water (also called salt water, salt-water or saltwater) is water with salt in it. It often means the water from the seas and oceans. When scientists measure salt in water, they usually say they are testing the salinity of the water, salinity is measured in parts per thousands or ppt. Most sea water is about 35 ppt salt. Salt water is more dense than fresh water.
The troposphere starts at the Earth’s surface and extends 8 to 14.5 kilometers high (5 to 9 miles). This part of the atmosphere is the most dense. Almost all weather is in this region.
The stratosphere starts just above the troposphere and extends to 50 kilometers (31 miles) high. The ozone layer, which absorbs and scatters the solar ultraviolet radiation, is in this layer.
The mesosphere starts just above the stratosphere and extends to 85 kilometers (53 miles) high. Meteors burn up in this layer
The thermosphere starts just above the mesosphere and extends to 600 kilometers (372 miles) high. Aurora and satellites occur in this layer.
The ionosphere is an abundant layer of electrons and ionized atoms and molecules that stretches from about 48 kilometers (30 miles) above the surface to the edge of space at about 965 km (600 mi), overlapping into the mesosphere and thermosphere. This dynamic region grows and shrinks based on solar conditions and divides further into the sub-regions: D, E and F; based on what wavelength of solar radiation is absorbed. The ionosphere is a critical link in the chain of Sun-Earth interactions. This region is what makes radio communications possible.
This is the upper limit of our atmosphere. It extends from the top of the thermosphere up to 10,000 km (6,200 mi).
- The term “cryosphere” comes from the Greek word, “krios,” which means cold.
- Ice and snow on land are one part of the cryosphere. This includes the largest parts of the cryosphere, the continental ice sheets found in Greenland and Antarctica, as well as ice caps, glaciers, and areas of snow and permafrost. When continental ice flows out from land and to the sea surface, we get shelf ice.
- An iceberg is ice that broke off from glaciers or shelf ice and is floating in open water. To be classified as an iceberg, the height of the ice must be greater than 16 feet above sea level and the thickness must be 98-164 feet and the ice must cover an area of at least 5,382 square feet.
- Bergy bits and growlers can originate from glaciers or shelf ice, and may also be the result of a large iceberg that has broken up. A bergy bit is a medium to large fragment of ice. Its height is generally greater than 3 feet but less than 16 feet above sea lvel and its area is normally about 1,076-3,229 square feet.
- Growlers are smaller fragments of ice and are roughly the size of a truck or grand piano.
- Snow refers to forms of ice crystals that precipitate from the atmosphere and undergo changes on the Earth’s surface.
- Ice sheets – a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km2, this is also known as continental glacier. Ice sheets are bigger than ice shelves or alpine glaciers.
- Sea ice is frozen ocean water. It forms grows and melts in the ocean. In contrast, icebergs, glaciers, and ice shelves float in the ocean but originate on land.
- Permafrost is a permanently frozen layer below the Earth’s surface. It consists of soil, gravel, and sand, usually bound together by ice. Permafrost can be found on land and below the ocean floor. It is found in areas where temperatures rarely rise above feeling.
- Atom – the smallest constituent unit of ordinary matter that has the properties of chemical element.
- Molecule – is the smallest particle in a chemical element or compound that has the chemical properties of that element or compound. Molecules are made up of atoms that are held together by chemical bonds.
- Macromolecule – a very large molecule, such as protein commonly created by polymerization of smaller subunits (monomers). They are typically composed of thousands of atoms or more.
- Organelle – is a specialized subunit within a cell that has a specific function. It is a tiny cellular structure that performs specific functions within a cell.
- Cell – the basic structural, functional and biological unit of all known living organisms.
- Tissue – an ensemble of similar cells from the same origin that together carry out a specific function.
- Organ – or viscus is a collection of tissues joined in a structural unit to serve a common function.
- Organ System – is a group of organs that work together to perform one or more functions.
- Organism – any contiguous living system, such as an animal, plant, fungus, protist, archaeon, or bacterium. All are capable of some degree of response to stimuli, reproduction, growth and development and homeostasis.
- Population – the number of all the organisms of the same group or species, which live in a particular geographical area, and have the capability of interbreeding.
- Community – a small or large social unit who have something in common.
- Ecosystem – a community of living organisms in conjunction with the nonliving components of their environment, interacting as a system.
- Biome – a large community of plants and animals that occupies a distinct region.
- Biosphere – the global ecological system integrating all living beings and their relationships, including their interaction with elements of the lithosphere, geosphere, hydrosphere, and atmosphere.