|Earth & Space Science Concepts Study Sheet
Earth's Origin and Dimensions
According to the proto-planet hypothesis, the solar system began as a rotating cloud of gas and dust which condensed into the sun, planets and moons; the oceans formed from steam released from volcanoes. Earth's inner and outer cores, the mantle and the crust, including the lighter continents, formed as a result of differentiation in density. Scientists give a date of 4.6 billion years for the origin of Earth.
Because Earth is an oblate spheroid (flattened at poles, thicker around equator), objects weigh more at the poles, less at the equator. Weight is dependent on an object's distance to the center of Earth. Eratosthenes measured the circumference of Earth by determining the relationship between the distance and angle between two places -on Earth's surface. Earth's average density is 5.5 g/cm3, but its surface density is only 2.8 g/cm3, so geologists theorize that Earth's core is much denser and made of nickel and iron.
Minerals are naturally occurring, inorganic solids with definite crystalline chemical compositions. Only eight elements make up 98.5% of the minerals which make up the rocks of Earth's crust. Minerals can be identified by physical tests such as hardness, color, luster, specific gravity, cleavage and crystal shape. Ionic bonds form between metals and nonmetals that form ions; covalent bonds form between minerals that share their electrons. All silicate minerals have the silica tetrahedron as a building block.
The rock cycle produces sedimentary, igneous, and metamorphic rocks through the processes of erosion, burial, lithification, and plate tectonics. Igneous rocks form at the surface from lava and inside the crust from cooling magma, Sedimentary rocks form from weathered or precipitated fragments which are buried and lithified under pressure. Agents of erosion, such as running water, can sort sediments by size. Any kind of rock can alter to metamorphic if it undergoes extreme temperature and pressure changes.
Mineral Resources and Energy Production
Renewable resources, such as wood and water (through the water cycle) can be replaced by nature. Nonrenewable resources, such as iron or petroleum cannot be replaced. Mineral resources refer to the total amount of a mineral, whereas mineral reserves refers to the amount that can be mined profitably. Fossil fuels, such as petroleum and coal, are formed from ancient organisms; there are limited supplies of petroleum and natural gas worldwide. Large quantities of 'oil are stored in oil shale and tar sands, but presently they cannot be extracted profitably. Wind power, solar power, water power, and geothermal power are energy sources that do not use fuel, but which have other limiting characteristics. Energy wastes and their products, such as acid rain, toxic wastes and nuclear waste are environmental and political problems of our society.
Topographic maps are the most detailed of maps and show the features of land through the use of contour lines. Contour lines point upstream as they cross rivers. Geologic maps indicate rock types; hydrologic maps show the presence of surface and groundwater.
Weathering and Soils
Weathering is the wearing down of rock into fragments; erosion is removal of weathered materials by glaciers, running water, wind and waves. Weathering is mechanical if the weathered products are chemically the same as the parent rock, weathering is chemical if the weathered product is chemically different from the parent rock. Different weathering rates result from differences in climate and rock composition. Of the common minerals quartz is the most resistant to weathering. Soil is the end result of-weathering; mature soil consists of -three horizons: topsoil, which contain organic material (humus), subsoil which contains clay and soluble minerals leached from the topsoil, and weathered bedrock. Soils can be transported from another area by streams, glaciers or wind or they may reside immediately above the parent rock from which they formed. Soil may be depleted if crops are not rotated. Soils in dry areas with high evaporation can become salinized which reduces crop productivity. Various agricultural practices, like contour farming and terracing can reduce soil erosion.
Water Cycle and Groundwater
Most of the 3% of Earth's fresh water (97% is saltwater.) is frozen in glaciers; much of the rest is stored underground as groundwater. Water budgets relate the amount of water that precipitates or is stored in the ground in a particular area to how much is lost to evaporation or runs off as surplus. Water is continually recycled by the processes of evaporation, condensation (Clouds are water droplets or crystals-not vapor.), precipitation, percolation and runoff. The capacity for air to hold water vapor is dependent on its temperature, so relative humidity changes from morning to night. The water table is the surface of stored water in the ground.
Permeable rock is rock that can transmit water. In sorted round particles (clay, sand, pebbles, cobbles) of different sizes, the percent porosity remains the same regardless of particle size. Permeability (rate of flow) increases as particle size increases. The amount of capillary water retained increases with smaller particle size because of increased surface area.
Except in areas of volcanism, groundwater is cold. Below 40 meters the temperature gradually warms with depth from Earth's 'interior heat.
Karst topography results in areas where the bedrock is limestone because acid rain slowly dissolves limestone which is made of the mineral calcite. Features of karst topography are: sinkholes, caves, lost rivers, and underground drainage.
Streams: Running Water
River systems begin as young mountain streams which have a high gradient, high velocity, clear water, straight path, waterfalls, rapids, and eventually canyons and alluvial fans. Erosion occurs mostly on the stream bed until the gradient becomes more gentle; then lateral erosion becomes more prominent and the stream slows down, begins to form meanders (curves), sandbars, cutoffs, ox-bow lakes and deltas. In a meander, erosion occurs on the outside curve and deposition occurs on the inside curve. Divides (highest ridges) divide continents into the drainage basins that produce river systems such as the Mississippi River System.
Glaciers are large bodies of ice that flow under their own weight. Valley glaciers form on mountain tops and flow down mountain valleys producing cirques, hanging valleys, horns, aretes, and moraines. Continental glaciers are large enough to actually cover mountains; they produce features such as kettle lakes, eskers (winding mounds from floor of glacial stream), drumlins (canoe-shaped hills of till), and moraines (such as the end moraine of Long Island). Till is unsorted material dumped by a glacier; outwash is sorted material deposited by streams inside the glacier. Canada and the northern part of the United States was covered by a continental glacier that receded 12,000 years ago.
Wind as an Erosive and Depositional Force
Loess is a silt-sized, wind deposited sediment. Most water waves result from wind; some water waves erode shorelines producing features such as sea cliffs and stacks; other waves deposit sand to produce depositional beaches. Waves are described by their length, height, period and speed. A tsunami is a wave produced by an earthquake on the sea floor.
According to the theory of plate tectonics, Earth's crust is made of rigid plates that cover Earth's surface and that move due to convection currents in the underlying asthenosphere. Ocean crust forms as plates diverge at mid-ocean ridges. Earthquakes occur in California where the Pacific Plate and the North American Plate slide past each other. Converging plates form faulted and folded mountain systems where two continental plates collide; converging plates form trenches and volcanic mountain chains where an ocean plate subducts another ocean plate or a continental plate. Alfred Wegener laid the foundation for the plate tectonic theory when he studied the similar shapes of adjoining continents as well as the correlation of fossils and rock types. Today additional evidence, such as magnetic polarity reversals, heat flow patterns, and sediment age patterns at diverging boundaries add credence to the plate tectonic theory.
An original continent (craton) can grow when land masses (terranes) from a neighboring plate collide with and become attached to the craton.
Igneous Activity: Volcanic and Plutonic
Molten rock below the surface is called magma; when magma reaches the surface, gases escape which result in a change in composition; the liquid is then called lava. Magmas are initially mafic (because of the high concentration of iron and magnesium in the asthenosphere and ocean crust), but when mafic magma works its way through a continent it becomes felsic as a result of incorporating continental materials, especially silicates and water. Felsic magma contains more dissolved gases and produces violent eruptions when it reaches the surface. Ash, lapilli, bombs, and blocks are examples of different sizes of solid fragments of lava.
Volcanoes occur at mid-ocean ridges (Mid-Atlantic Ridge; Eldfell, Iceland), hot spots (Hawaiian Islands, Iceland) and near the boundary of subduction zones (Cascades, Andes). Trenches occur on the boundaries of subduction zones.
Magma that does not make it to the surface cools to become plutons, such as sills (magma squeezed between sedimentary layers), dikes (magma cutting across rock layers), laccoliths mushroom-shaped intrusions that can produce dome mountains) and volcanic necks.
An earthquake is a release of energy due to pressure changes in Earth's crust and are usually related to plate movement. The focus is the place inside Earth where the earthquake begins; the epicenter is the spot on the surface immediately above the focus. P-waves (compressional) and S-waves (shear) travel inside Earth. S-waves cannot travel through liquids and have been the source of evidence that Earth's outer core is liquid. The boundaries between the crust (Moho), mantle, and cores have been determined by studying earthquake waves. L-waves travel on Earth's surface like ripples and cause surface damage.
Seismographs record all three types of earthquake waves and can be used to determine the distance to an earthquake from the seismograph due to different arrival times of P and S waves. With three seismographs, -at a minimum, one can also determine the epicenter of the earthquake and its magnitude. The Mercalli Scale, the Richter Scale and seismic moment are all ways of describing the magnitude or intensity of an earthquake. Seismic moment gives the most accurate assessment of the total energy given off by a particular earthquake.
Earthquakes usually occur on a subduction zone (deep: Alaskan quake), sliding boundary (shallow: San Andreas Fault), or mid-plate zone (deep: New Madrid, MO). Shallow earthquakes do not travel for long distances because the waves are absorbed by loose earth materials.
Mountains and Plateaus: Structural Geology
Collision mountains are the result of reverse (compressional) faulting; in a reverse fault the hanging wall is raised. Reverse faults can produce plateaus when a large block of crust is thrust upward in a basically horizontal position. Compression can also produce folded mountains if the compression occurs deep enough and in a rock type that tends to plasticize. The upfold of folded rock strata (hill shape) is an anticline; the downfold (valley shape) is a syncline. When faulting occurs due to tension, a center portion sinks (normal fault) and a graben like Death Valley can form. Strike-slip faulting (horizontal movent such as occurs on a sliding boundary) does not produce mountains. Dome mountains are nearly circular folded mountains produced by either a laccolith or by upward tectonic pressure without the involvement of magma.
Connecticut formed during several compressional mountain building periods in which the Western and Eastern Uplands developed as terranes collided with the North American craton thus forming Pangaea. Connecticut's Central Valley is a graben which formed as Pangaea began to break up from tension that produced faulting, tilting and sinking. Connecticut's surface has been altered by the recent glaciation. Connecticut's thin soil is transported glacial soil.
Seventy percent of Earth's surface is covered with oceans that are four times deeper than continents are high. Sea water is 3 5 parts per thousand dissolved solids. Differences in salinity can be used to trace water masses and currents. Currents cause sea water to be well-mixed, having the same relative proportions of ions in all parts of the oceans. Ocean currents are produced by wind or by differences in density due to salinity and temperature. Two surface currents in the North Atlantic Ocean are the Gulf Stream which carries water from the equator northeasterly toward Europe and which carries a warm climate and the Labrador Current which carries icebergs and fog southward along eastern North America.
The mixed surface waters of the oceans contain light and plants; below the mixed layer temperature drops rapidly 'in the thermocline; below that sea water is extremely cold and animal life is sparse. Unique communities of organisms live near hydrothermal vents.
Salt and magnesium are mined directly from sea water. Manganese nodules are mined from the sea floor.
I Sea floor features, such as continental shelves and rises, abyssal plains, trenches, midocean ridges, submarine canyons and guyots, are the products of plate tectonics, deposition and erosion. Four groups of sea floor sediments, each with a different origin, are oozes, muds and clays, turbidites, and authigenic sediments.
Earth's Environment in Space
Telescopes collect electromagnetic energy from high energy gamma rays to low energy radio waves. Most telescopes are more effective placed in space, away from the turbulent atmosphere which reduces the resolution of signals.
The Doppler Effect (Red Shift) of visible light can be used determine the relative motion of stars and galaxies. Astronomers use the H-R Diagram to relate the luminosity and temperature of stars and to group stars by their relative ages.
Earth is one of nine planets that revolve around the Sun, a star. Most of the planets have moons revolving around them. Asteroids (too small to be considered planets) and comets (with highly eccentric orbits) are also members of the solar system The solar system is a member of the Milky Way Galaxy, a spiral galaxy.
Kepler's Laws of Planetary Motion state that planets travel in ellipses with the Sun at one focus; that planets sweep equal areas in equal times (traveling faster at perihelion); and that the period squared of a planet is equal to the cube of its distance from the Sun. Galileo's Law of Universal Gravitation states that the gravitational force between two objects is directly proportional to the mass of the objects and inversely proportional to the distance squared between the objects.
Stars form from condensing clouds of gas and dust that begin to glow as they become protostars, but become true stars only after hydrogen fusion has begun to occur in the star's core. Once the hydrogen in the core of a star has changed to helium, the star becomes a red giant or supergiant. In old age, massive stars explode into supernovas, and become neutron stars, pulsars, or black holes; less massive stars become white dwarfs.
Stars can give off variable light because they are binaries that eclipse each-. other, because they are novas or supernovas, or because they are pulsating stars, such as Cepheid variables, which change energy output in a regular, cyclical manner.
During a total solar eclipse, the dark part of moon's shadow called the umbra reaches a small part of Earth's surface. During a lunar eclipse, Earth's shadow covers the Moon.
Tides are caused by the gravitational pull of the Moon and the Sun on Earth. Spring tides have a high range from high tide to low tide because the Earth, Moon, and Sun are lined up. When the Moon and Sun are pulling on Earth from different angles, neap tides occur.
The rotation of Earth (spin on its axis) produces might and day. The revolution of Earth on its tilted axis produces years with seasonal variations.
Paleontologists date fossils and rock in relative and absolute time. Relative time is determined using the laws of Superposition (Oldest layer is on bottom), the Law of Cross-Cutting Relationships (Intrusions are younger than rocks they intrude) and ]Law of Included Fragments (Fragments are older than rocks in which they are found). Gaps in the rock record due to erosion are unconformities. Tree rings and varves (seasonal sediment in lakes) can be used to date ages of trees and lakes. The half-lives of several radioactive elements can be used to date fossils and rocks. In one half-life, half of a radioactive element will have decayed to a stable element. Carbon-14 is used to date relatively young organic remains-up to 100,000 years old. Uranium, rubidium, and potassium isotopes are used to date rock of various ages.
The geological time scale subdivides the four eras of Earth's history into periods which are subdivided into epochs. The first and largest segment of geologic time is called the Pre-Cambrian. There was very little life until the beginning of the second era, the Paleozoic, during which most organisms lived in the sea. Dinosaurs evolved in the Mesozoic Era, also known as the Age of Reptiles. The Cenozoic Era is commonly called the Age of Mammals. We live in the Recent Epoch of the Quaternary Period of the Cenozoic Era. Divisions on the time scale are determined by the appearances and disappearances of species of plants and animals.