Lowland areas have no gravity decrease {isostatic compensation}, because lowland areas have thin crust, with mantle closer to surface. Mountain areas have no gravity increase, because mountains float on mantle, pushing heavier mantle aside.
The figure eight {analemma} on globes shows Sun declination for day of year.
Earth locations use lines {longitude}| {meridian} running from pole to pole. Longitude is in degrees, up to 180 degrees east or west from the prime meridian that runs through Greenwich, England.
At meridian 180 degrees east or west {International Date Line}|, time adds one day if traveling east, and time subtracts one day if traveling west.
The reference meridian {prime meridian}| runs through Greenwich, England, at zero degrees longitude.
Earth locations use lines {latitude, Earth}| parallel to equator. Latitude is in degrees. Equator is 0 degrees latitude. North Pole is 90 degrees north latitude. South Pole is 90 degrees south latitude.
The reference latitude {equator}| runs horizontally around Earth middle and is zero degrees latitude.
People cannot see Sun in winter in Southern Hemisphere above 66.5 degrees south latitude {Antarctic Circle}|.
People cannot see Sun in winter in Northern Hemisphere above 66.5 degrees north latitude {Arctic Circle}|.
Sunlight falls straight down on Midsummer Day at 23.5 degrees north latitude {Tropic of Cancer}| in Northern Hemisphere.
Sunlight falls straight down on Midsummer Day at 23.5 degrees south latitude {Tropic of Capricorn}| in Southern Hemisphere.
Zones {semitropics}| can be between tropic and temperate zones.
Earth climates {climate}| {clime} can be wet or dry.
dry
Deserts and steppes are 25% of Earth land area. Deserts and steppes have large yearly and daily temperature variation, have rain in summer if at high altitude, have rain in winter if at low altitude, and have high winds.
wet
Pacific Ocean surface currents typically make monsoons. With warm El Ni-o, west North America has wet weather.
wet: plants
Plants absorb rain in roots and evaporate water from leaves, allowing rain to form and fall in one place. If plants die, water goes into ground, and rain is less.
core and surface temperature
Heat flow from core has no effect on Earth surface temperature.
Tropical winds push warm water north along east North-American coast {conveyor belt}. It becomes denser at it cools and sinks near Greenland, allowing flow to continue. Europe receives warm water that returns south in deep water along east Atlantic Ocean. If melted snow enters North Atlantic, the cold fresh water prevents warmer salty water from sinking, and conveyor belt turns off. Cold, dry winds flow east around north.
Above 4000 to 6000 feet is line {forest line}| where forest stops.
Temperate climates can have summer-like weather {Indian summer}| in fall.
Earth receives radiation {insolation}| from Sun. As Venus, Jupiter, and Saturn have different relative positions, Earth orbit varies, which changes insolation. Sun can brighten and darken, changing insolation.
Earth radiates heat {heat radiation}. Soot, particles, and clouds {aerosol, atmosphere} affect heat radiation.
Chemicals can prevent heat from escaping Earth {greenhouse effect} {global warming}|. Carbon dioxide, methane, ozone, nitrous oxide, and chlorofluorocarbons (CFC) prevent heat radiation from Earth by absorbing infrared radiation. Methane comes from gas and oil wells, landfills, and waste processing. Carbon soot and other dark pollution particles trap heat.
reflective
Sulfate aerosols are reflective and prevent insolation. Clouds affected by aerosols are brighter, last longer, are reflective, and prevent insolation. Volcanoes add soot that blocks sunlight.
ocean
Ocean absorbs excess heat.
forests
Deforestation reduces dark areas and reduces heat absorption.
speculation
Ships with windmills can hydrolyze seawater in windstorms or in normal winds to make and store hydrogen and oxygen, as well as upwell cold seawater from the deep to cool hot spot.
Carbon dioxide, chlorofluorocarbons, ozone, nitrous oxide, and methane {greenhouse gas}| prevent heat radiation from Earth by absorbing infrared radiation.
If ice starts to form on Earth, it reflects more light, Earth gets icier, and water in air becomes less {White Earth climate}, while carbon dioxide forms into carbonates at equator. Perhaps, an Earth ice covering reflected light and kept Earth cold for 10 million years, with no rainfall, dry winds, no water vapor, and low carbon dioxide. Volcanoes release carbon dioxide can warm Earth again over the ten million years, because carbon dioxide does not go into plants or carbonates in cold weather.
Above 4000 to 6000 feet, climate {highland climate}| has low air pressure, low humidity, large daily temperature range, large annual temperature range, and no forests.
More evaporation than precipitation causes very dry climate {arid climate}|.
Arid climates {desert}| can have cactus and bushes.
More evaporation than precipitation causes dry climate {semiarid climate}.
Semiarid climates {steppe}| can have grass.
Humid rainy climate {tropical}| near equator has narrow temperature range, average temperature greater than 65 F, and dry winters if on west coast.
Seasonal humid climate {subtropical}| at 25 to 40 degrees latitude has dry summers if on west coast.
Humid climate {temperate climate}| at 40 to 60 degrees latitude has summer rainy season and rapid weather changes. It has Indian summers, January thaws, blizzards, and heat waves if on east coast or in interior. It has small temperature range if on west coast.
At 50 to 65 degrees latitude, climate {boreal}| has long cold winters, large annual temperature range, small precipitation in summer, targa, permafrost, long winter nights, long summer days, many lakes, and little topsoil.
Boreal climate has regions {targa}| with sparse conifer forests.
Boreal climate has frozen subsoil and rock {permafrost}|.
At 65 to 90 degrees latitude, cold climate {polar, climate}| has no forest, no sunlight for six months, large annual temperature range, little rain, ice caps, and tundra. Ice caps are 8% of Earth surface.
Polar climate has land {tundra}| with small and sparse vegetation.
Earth layers {planet layer} are core, mantle, and crust.
Earth center {core, Earth} {Earth core} has been the same since 3,500,000,000 years ago, after heating and layering ceased.
Earth center {inner core, Earth} is solid iron with some nickel and cobalt. Inner core has pressure 20,000 tons/in^2, temperature 4000 F to 8000 F, and radius 800 miles.
Layer {F shell} above inner core is 300 miles thick.
Layer {outer core} above F shell is liquid iron with some nickel, cobalt, silicon, and sulfur. Outer core has pressure 10,000 tons/in^2 and is 1375 miles thick.
Layer {D shell} above outer core is several hundred miles thick.
Above core D shell is layer {mantle, Earth}|. Mantle is 1800 miles thick and contains 80% of Earth volume.
temperature
Mantle temperature at 500,000 meters deep is 2300 K. Mantle temperature at 100,000 meters deep is 1500 K. Temperature increases with depth, 1 C every 30 meters. Lower mantle, below 700,000 meters deep, has convection currents caused by heat.
density
Below 650,000 meters deep, density is 5.5 g/cm^3. Between 400,000 to 650,000 meters deep, density is 4.5 g/cm^3. Above 400,000 meters deep, density is 3.5 g/cm^3. In upper mantle, which is 50 miles thick, density is 2.6 g/cm^3.
rock types
Lower mantle has dunite, which is mostly olivine, with some peridotite. Olivine has magnesium, silicon, and oxygen. Upper mantle has serpentine, at 50 miles to 100 miles above olivine, where 0.1% water and some carbon dioxide change olivine and pyroxene into serpentine and hydrogen {serpentinization}.
Iron and magnesium silicate olivines are 100,000 meters to 250,000 meters deep, in lower upper mantle {asthenosphere}.
Iron and magnesium silicates {dunite} are mostly olivine and make lighter-color veins in upper mantle.
Iron and magnesium silicates {eclogite} are in mantle.
Above Mohorovicic discontinuity is surface layer {crust}|.
Layer {Mohorovicic discontinuity} above mantle is thin.
Upper-mantle serpentine layer and lower-crust sial layer make layer {lithosphere}.
Lower crust is a three-mile thick heavy iron-and-magnesium-silicate basalt layer {sial layer}. Basalt forms from melted upper-mantle serpentine under lower pressure. Basalt crust density is 2.3 g/cm^3.
Upper crust has landmasses {continent, land}|. Continents now cover 25% of Earth surface. Continents average 20 miles thick and can be 40 miles thick. True continent edge is below ocean at continental-shelf edge, up to 400 miles from shore.
rocks
Continental rock is permanent, with no recycling back into crust or mantle. Continents are mostly granite, with density 2.1 g/cm^3 {sima layer}, so they rise above seas.
formation
First continent rocks appeared 4,000,000,000 years ago, as continents grew from upper mantle. After first continent-formation period ended 3,500,000,000 to 3,800,000,000 years ago, continents were 5% to 10% of crust. First-formation-period rocks are in Isua in southwest Greenland. These rocks have greenstone belts, granite-gneiss terrains, or igneous rocks cutting through them from upper mantle. Greenstone belts contain ultramafic rock and mafic rock, as xenolith.
Second continent-formation period, from 2,600,000,000 to 2,900,000,000 years ago, formed 50% to 60% of continental Archean rock.
Third continent-formation period was 1,700,000,000 to 1,900,000,000 years ago.
Fourth continent-formation period was 900,000,000 to 1,100,000,000 years ago.
Fifth continent-formation period was 600,000,000 years ago.
Igneous rock {mafic rock} can be mostly iron and magnesium. Mantle basalt, ocean-floor bedrock, and lava are mafic.
Greenstone belts contain volcanic rock {ultramafic rock} and partially melted mafic rock, which have no water.
Greenstone belts contain ultramafic and mafic rock, which have no water {xenolith}.
The second continent formation period, from 2,600,000,000 to 2,900,000,000 years ago, formed 50% to 60% of continents {Archean rock}.
Continent has independent masses {subcontinent} that have come together by plate movement.
Earth has magnetic fields {magnetic field, Earth} {Earth magnetic field}, because thermal convection from iron-solidification latent heat and escape of inner-core iron oxide and iron sulfide causes liquid-iron outer-core spin {geodynamo}. Magnetic-field strength is 10,000 gauss at Earth surface. Magnetic field is decreasing. Magnetic field reverses polarity randomly, approximately every 250,000 years. Earth magnetic field has had same polarity for last 780,000 years.
Earth has magnetic equator {aclinic line} between magnetic poles.
Ions from Sun can enter Earth atmosphere at poles, along magnetic-field lines. They hit atmosphere atoms and make light displays {aurora, pole}| that look like colored curtains, at North Pole {aurora borealis} {northern lights} or South Pole {aurora australis}.
Earth has magnetic poles {magnetic pole, Earth}|. Magnetic North Pole is in north Canada, not at spin North Pole.
From 600 to 40,000 miles above Earth surface, magnetic fields {magnetosphere} {Van Allen radiation belt} deflect weak cosmic rays and absorb ions from Sun. Sun ions push magnetosphere out from Sun.
Meteoroids can enter Earth atmosphere and heat until they make light {meteor}|. Every year, Earth adds 1000 to 1,000,000 tons of meteor dust.
Stony meteorites can have tiny olivine and pyroxene clumps {chondrule}.
Stony meteorites {chondrite} can have olivine and pyroxene chondrules. Stony chondrites are 90% of all meteorites.
Stony meteorites {achondrite} can have no clumps.
Space objects {meteoroid}| can be broken-planet pieces from asteroid belt.
Meteors {meteorite}| can hit ground. Largest meteorite weighed 30 tons. A 15,000-ton meteorite formed Canyon Diablo Meteor Crater, 4100 feet across and 600 feet deep, in Arizona. Meteorites {iron meteorite} can have more than 98% iron and nickel. Meteorites {stony iron meteorite} can have 50% nickel-iron and 50% olivine. Meteorites {stony meteorite} can be mostly rock, with little nickel and iron.
Early Moon meteoroid impact melted glass, which splashed up and then landed on Earth in a strip of achondrite drops {tektite}|.
Continental plates move {plate tectonics}|, when olivine from upper mantle comes through rift in crust basalt, pushing plates apart. See Figure 1.
Plates can slide into each other, pushing one down and one up to make trenches and mountains. See Figure 2.
rates
Pushed plates move two centimeters per year. Sea-floor movement in Chile is 15 centimeters per year.
results
Upwelling at ocean ridges can make volcanoes with basalt lavas. Old rift valleys can fill with aulacogens.
evidence
Coal is in Antarctica. Similar fossils are on separated continents. All over world, iron in volcanic rocks aligns in many different directions, instead of only north and south. East South America and west Africa have similar coastlines.
Sea floor is spreading away from Mid-Atlantic Ocean Ridge. Basalt at Mid-Atlantic Ocean Ridge is younger than basalt near continents. Mid-Atlantic-Ocean Ridge basalt shows alternating iron-particle orientations every 700,000 years, when Earth magnetic field reversed. Sediment at Mid-Atlantic Ocean Ridge is less than at continent edges.
Pacific-Ocean floor has thicker sediments and is older than Atlantic-Ocean floor. Atlantic-Ocean floor is 200,000,000 years old. Atlantic-Ocean sediment averages only several thousand feet thick and in some places is much thinner. If ocean floor had not changed for 200,000,000 years, sediment would be several miles thick.
Six major, and many minor, crust pieces {continental plate} {crustal plate}| float on upper mantle.
Continental plates move when olivine from upper mantle comes through basalt crack {rift}|, pushing plates apart. Pushed plates move one inch per year. Atlantic-Ocean middle has rift north to south that rises above sea level at Iceland, Azores, and Ascension Islands. Southeast South Pacific Ocean and central Indian Ocean have rifts.
Old rift valleys can fill with sediment {aulacogens}.
Along rift, lava makes mountain ridge, with valley down middle {sea floor spreading}|.
Continent granite {shield, continent}| can be at surface.
Rock layers can have shape like upside-down V {anticline}.
Rock layers can bend up or down {monocline} {flexure}.
Rock layers can have shape like V {syncline}.
Slips along rock faults cause movements {earthquake}|. Slow plate movements and collisions lead to sudden shifts of one plate against the other. Earthquakes can be several miles deep or even in mantle under ocean trenches. After earthquake, Earth vibrates at low frequency for several days. About 20 major earthquakes and 10^6 minor ones happen each year. Major earthquakes have been in China 1976, Tokyo 1923, San Francisco 1906, Lisbon 1755, Calcutta 1737, and China 1556.
Rock has big cracks {joint, rock}.
Earthquakes can be along rock fractures {fault}|.
Instruments {seismograph}| can measure Earth movements.
Seismographs can use logarithmic scales {Richter scale}|, from 1 up. Largest earthquake was 8.5.
Earthquakes {silent earthquake} can be slow and quiet. Perhaps, water percolation from rain or from trapped water in rocks causes them.
Earthquake shaking can cause loose wet sandy soil to become like quicksand {soil liquefaction}|.
Earthquakes under ocean can make fast waves, which then slow near shore and bunch to make towering waves {tsunami}|.
Earthquake shocks can travel through crust as slow surface waves or through Earth interior as very fast primary waves {P wave}.
Earthquake shocks can travel through solids as fast secondary shock waves {S wave}.
Both horst and graben processes form mountains {orogeny}.
Mountain building processes can make large lowered masses {graben}|, as in Death Valley USA, Red-Sea basin, and East-Africa rift valleys.
Mountain building processes can make large raised masses {horst}|, as in Sierra Nevada Mountains and Alps Mountains.
Upper-mantle convection currents rise near surface at 20 locations {plume, mantle} {hot spot, mantle}|. Plumes have 300,000 meters diameter. Plumes in crustal-plate middle can send alkali-rich basalt lava up to surface to form volcanoes, as in Hawaiian Islands.
Colliding plates can move straight into each other {pressure ridge} to make mountains, with no overriding. Alternatively, one plate can slide over other one, forming both mountains and ocean trenches.
Along rift, lava makes mountain range {ridge, mountain}|, with valley down middle.
At plate sides opposite from rifts, plates slide under other plates {subduction, plate}|. Plates meet {subduction zone}, and one plate goes up and the other goes down, at 45-degree angles. Plates can go 700 kilometers into mantle. Subduction is at North-America and South-America west coasts, at Asia east coast, and from Spain and north Africa to Italy, to Greece, to Turkey, to India, to Burma, to Celebes.
Ocean crust and underlying mantle {ophiolite} can uplift onto continent.
Colliding plates can make especially deep and steep ocean floor {trench}|.
Continents move on upper mantle {continental drift}|. Upper-mantle asthenosphere and possibly all mantle has stable constant one-inch-per-year convection currents, caused by heat. Currents provide energy to move continents. Continents have been drifting for last 2,000,000,000 years. Six major and many minor crustal plates float on upper mantle.
Plate movements make crust slide, fold, and fault {diastrophism}.
Increased fluid pressure, changed electrical resistivity, decreased Earth natural electric currents, increased deep-well-water radon content, changed seismic-wave travel time, and seismicity affect crustal-plate movements {dilatancy}. Dilatancy models earth movements as inelastic swelling. Steady stress increase splits crust, allowing water flow. If water flows in slower than cracks open, crust splitting slows. Then water under pressure quickly fills crack, causing sudden slip. Changes from compression waves to shear waves cause seismic-wave travel-time changes.
Continents are 10% lighter than crust, and crust is 10% lighter than upper mantle, so continents float on crust, which floats on upper mantle {isostasy}.
Plate movements {tectonic process}| make crust slide, fold, and fault in diastrophism.
Magma comes from mantle, 2 to 100 miles down, to surface {volcano}| through crust fissures. Magma then cools and hardens. Most of Earth water vapor and gases came from volcano eruptions.
types
Thick magma has more gas, is red hot, erupts explosively, and makes steep mountains. Thin magma has little gas, is white hot, and makes wide mountains.
examples
Famous volcanoes are Mount Vesuvius in Italy, which buried Pompeii [79]. Krakatoa in Indonesia exploded island [1869]. Mount Etna in Italy caused enormous avalanche and undersea mudslide [-6000] and started a huge tsunami: it is still active. Mauna Loa in Hawaii is active.
Volcanoes can erupt {volcanism} where plates collide, making andesite lava.
Magma can spread to make stock rock masses, which can be thousands of square miles wide {batholith}.
Volcano tops have craters {caldera}|.
Magma can flow into vertical rock fissures and cool and harden {dike, magma}.
Cylindrical columns {kimberlite pipe} from mantle to crust can have 300-meter diameter.
Magma {lava}| can reach surface.
Molten igneous rock {magma}|, mixed with gas and water vapor, comes from mantle, 2 to 100 miles down, to surface through crust fissures.
Magma can make underground pools {sill, magma}.
Magma can spread to make large rock masses {stock, rock}.
Earth temperature {temperature, Earth} increased until 130,000,000 years ago, then decreased until Ice Ages, and has remained almost the same since then. The year -8000 was warmest in recent history, until 20th century. Climate has been slowly cooling since then. Sea can rise or fall by 400 feet between Ice Age and warm period. Increased-volcanic-eruption periods correlate with Ice Ages, because volcanic dust reflects more sunlight and makes Earth cooler.
Strata can contain organic molecules {biomarker} from organism classes, because some cell-membrane lipids do not decompose.
Carbon isotopes are carbon-12, carbon-13, and carbon-14. Photosynthetic plants use more carbon-12 than carbon-13, so abundant plants lower carbon-12 ratio {isotope ratio, carbon} {carbon isotope ratio} in air. Air trapped in ancient rocks and ice can show relative amounts of photosynthetic plant life at past times.
Large meteors or comets and high volcanism can cause widespread death {catastrophe, Earth}.
meteor
Large meteor or comet hit 65 million years ago. Iridium level is higher in that rock stratum than in other layers. Iridium is more abundant in space than on Earth. That stratum also has pressure-shocked minerals.
volcanoes
Volcanic activity was high 443 million years ago, 374 million years ago, 251 million years ago, and 201 million years ago. Volcanoes put hydrogen sulfide, sulfur dioxide, carbon dioxide, and methane into air, which cause greenhouse effect and warm air.
ocean
With ocean warming, surface absorbs less oxygen, and chemocline rises. At high enough warming, chemocline comes to surface, and hydrogen sulfide enters air. Hydrogen sulfide kills land animals and plants directly. It also attacks ozone shield, allowing more UV radiation, which kills animals and plants.
Water absorbs oxygen. Water absorbs less oxygen at higher temperature, so oceans have less oxygen at surface and more at lower depths, which are cooler. At ocean bottoms, hydrogen sulfide comes from thermal vents. It rises and prevents further oxygen absorption at ocean depth {chemocline}. Below chemocline is high hydrogen sulfide, and above chemocline is high oxygen. Green sulfur bacteria and purple sulfur bacteria use hydrogen sulfide and are near ocean bottom. Photosynthetic organisms use dissolved carbon dioxide and sunlight so they stay near surface. Zooplankton use oxygen and so stay above chemocline.
Glaciers are largest every 100,000 years {glaciation era}, when Earth-axis tilt toward Sun minimizes, and perihelion shortest distance from Earth to Sun is in December in Northern Hemisphere, which has more land. Glaciers are smallest every 100,000 years, when Earth-axis tilt toward Sun maximizes, and perihelion shortest distance from Earth to Sun is in June in Northern Hemisphere, which has more land.
Continental {land mass} drift affects Earth temperature. When more land is in tropics, Earth absorbs more heat. When less land is at poles, glaciers decrease, reflective ice is less, and Earth reflects less heat.
Earth-axis tilt, axis wobble, and orbit cycles change sunlight amount that falls on Earth, in an overall cycle that caused Ice Ages {Milankovich model}. Earth-axis tilt cycles over 90,000 to 100,000 years. Earth axis wobble has a 39000-year to 42000-year cycle. Earth orbital path has a 17000-year to 21000-year cycle. Summer in Northern Hemisphere can be when Earth is closest to Sun, making hotter land temperatures.
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Date Modified: 2022.0225