Earth

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Earth

by Benjamin Boster

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talks

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In this episode of the I Can't Sleep Podcast, I read to you about the Earth. What a great planet on which we live! However, I read slowly to be sure you'll drift off before you learn anything. Happy sleeping!

Earth Sleep Geology Climate Change Biodiversity Relaxation Future Projection Podcasts

Meet your Teacher

Benjamin Boster

Pleasant Grove, UT, USA

Meet your Teacher

Benjamin Boster

Pleasant Grove, UT, USA

Transcript

Welcome to the I Can't Sleep Podcast, Where I read random articles from across the web to bore you to sleep with my soothing voice. I'm your host Benjamin Boster. Today's episode is from a Wikipedia article titled, Earth. Earth is the third planet from the sun and the only astronomical object known to harbor life. According to radiometric dating estimation and other evidence, Earth formed over 4. 5 billion years ago. Earth's gravity interacts with other objects in space, Especially the sun and the moon, Which is Earth's only natural satellite. Earth orbits around the sun in 365. 256 solar days, A period known as an Earth sidereal year. During this time, Earth rotates about its axis 366. 256 times, That is, A sidereal year has 366. 256 sidereal days. Earth's axis of rotation is tilted with respect to its orbital plane, Producing seasons on Earth. Gravitational interaction between Earth and the moon causes tides, Stabilizes Earth's orientation on its axis, And gradually slows its rotation. Earth is the densest planet in the solar system and the largest and most massive of the four rocky planets. Earth's outer layer, Lithosphere, Is divided into several rigid tectonic plates that migrate across the surface over many millions of years. About 29% of Earth's surface is land consisting of continents and islands. The remaining 71% is covered with water, Mostly by oceans, But also lakes, Rivers, And other fresh water, Which all together constitute the hydrosphere. The majority of Earth's polar regions are covered in ice, Including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, A liquid outer core that generates Earth's magnetic field, And a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, Life appeared in the oceans and began to affect Earth's atmosphere and surface, Leading to the proliferation of anaerobic and later aerobic organisms. Some geological evidence indicates that life may have arisen as early as 4. 1 billion years ago. Since then, The combination of Earth's distance from the sun, Physical properties, And geological history have allowed life to evolve and thrive. In the history of life on Earth, Biodiversity has gone through long periods of expansion, Occasionally punctuated by mass extinctions. Over 99% of all species that ever lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Most species have not been described. Over 7. 7 billion humans live on Earth and depend on its biosphere and natural resources for their survival. Etymology The modern English word Earth developed via Middle English from an Old English noun most often spelled Urd. It is cognates in every German language, And their ancestral root has been reconstructed as Urth. In its earliest attestation, The word Urth was already being used to translate the many senses of Latin terra and Greek ge, The ground, Its soil, Dry land, The human world, The surface of the world including the sea, And the globe itself. As with Roman terra, Telus, And Greek gaia, Urth may have been a personified goddess in Germanic paganism. Late Norse mythology included Juro, Urth, A giantess often given as the mother of Thor. Originally Urth was written in lowercase, And from Early Middle English its definite sense as the globe was expressed as the Earth. By Early Modern English many nouns were capitalized, And the Earth became, As often remained, The Urth, Particularly when referenced along with other heavenly bodies. More recently the name is sometimes simply given as Urth, By analogy with the names of the other planets. House styles now vary. Oxford spelling recognizes the lowercase form as the most common, With the capitalized form an acceptable variant. Another convention capitalizes Urth when appearing as a name, E. G. Urth's atmosphere, But writes it in lowercase when preceded by the, E. G. The atmosphere of the Earth. It almost always appears in lowercase in colloquial expressions, Such as, What on Urth are you doing? Occasionally the name Terra is used in scientific writing, And especially in science fiction to distinguish our inhabited planet from others, While in poetry Telus has been used to denote personification of the Earth. The Greek poetic name Gea is rare, Though the alternative spelling Gia has become common due to the Gea hypothesis, In which case its pronunciation is Gaea, Rather than the more classical Gea. The Greek poetic name Gia is rare, Though the alternative spelling Gaea has become common due to the Gaea hypothesis, In which case its pronunciation is Gaea, Rather than the more classical Gaea. There are a number of adjectives for the planet Earth. From Urth itself comes Urthly. From Latin Terra come Terran, Terrestrial and, By a French, Terrain. And from Latin Telus come Telurian, And, More rarely, Teluric and Telural. From Greek Gaia and Gaea comes Gaian and Gaean. An inhabitant of the Earth is an Urthling, A Terran, A Terrestrial, A Telurian, Or, Rarely, An Urthian. Chronology Formation. The oldest material found in the solar system is dated to 4. 5672 ± 0. 0006 billion years ago. By 4. 54 ± 0. 04 billion years ago, The primordial Earth had formed. The bodies in the solar system formed and evolved with the Sun. In theory, A solar nebula partitions a volume out of a molecular cloud by a gravitational collapse, Which begins to spin and flatten into a circumstellar disk, And then the planets grow out of that disk with the Sun. A nebula contains gas, Ice grains, And dust, Including primordial nuclides. According to nebular theory, Planetesimals formed by accretion, With the primordial Earth taking 10 to 20 million years to form. A subject of research is the formation of the Moon some 4. 53 billion years ago. The leading hypothesis is that it was formed by accretion from material loose from Earth after a Mars-sized object named Theia hit Earth. In this view, The mass of Theia was approximately 10% of Earth's. It hit Earth with a glancing blow and some of its mass merged with Earth's. Between approximately 4. 1 and 3. 8 billion years ago, Numerous asteroid impacts during the late heavy bombardment caused significant changes to the greater surface environment of the Moon, And by inference, To that of Earth. Geological History Earth's atmosphere and oceans were formed by volcanic activity and outgassing. Water vapor from these sources condensed into the oceans, Augmented by water and ice from asteroids, Protoplanets, And comets. In this model, Atmospheric greenhouse gases kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3. 5 billion years ago, Earth's magnetic field was established, Which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed when the molten outer layer of Earth cooled to form a solid. The two models that explain land mass propose either a steady growth to the present-day forms, Or, More likely, A rapid growth early in Earth's history, Followed by a long-term steady continental area. Continents formed by plate tectonics, A process ultimately driven by the continuous loss of heat from Earth's interior. Over the period of hundreds of millions of years, The supercontinents have assembled and broken apart. Roughly 750 million years ago, One of the earliest known supercontinents, Rodinia, Began to break apart. The continents later recombined to form Pannotia 600 to 540 million years ago, Then finally Pangaea which also broke apart 180 million years ago. The present pattern of ice ages began about 40 million years ago, And then intensified during the Pleistocene about 3 million years ago. High-latitude regions have since undergone repeated cycles of glaciation and thaw, Repeating about every 40, 000 to 100, 000 years. The last continental glaciation ended 10, 000 years ago. Evolution of Life and Evolution Chemical reactions led to the first self-replicating molecules about 4 billion years ago. A half billion years ago, The last common ancestor of all current life arose. The evolution of photosynthesis allowed the sun's energy to be harvested directly by light forms. The resultant molecular oxygen accumulated in the atmosphere and due to interaction with ultraviolet solar radiation formed a protective ozone layer in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes. True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, Life colonized Earth's surface. Among the earliest fossil evidence for life is microbial mat fossils found in 3. 48 billion year old sandstone in Western Australia. Biogenetic graphite found in 3. 7 billion year old metasedimentary rocks in Western Greenland. And remains of biotic material found in 4. 1 billion year old rocks in Western Australia. The earliest direct evidence of life on Earth is contained in 3. 45 billion year old Australian rocks showing fossils of microorganisms. During the Neo-Proterozoic 750-580 million years ago, Much of Earth might have been covered in ice. This hypothesis has been termed snowball Earth and it is of particular interest because it preceded the Cambrian explosion when multicellular life forms significantly increased in complexity. During the Cambrian explosion 535 million years ago, There have been five mass extinctions. The most recent such event was 66 million years ago when an asteroid impact triggered the extinction of the non-avian dinosaurs and other large reptiles that spread some small animals such as mammals, Which at the time resembled shrews. Human life has diversified over the past 66 million years and several million years ago an African ape-like animal gained the ability to stand upright. This facilitated tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, Which led to the evolution of humans. The development of agriculture and civilization led to humans having an influence on Earth and the nature and quality of other life forms that continues to this day. Future Earth's expected long-term future is tied to that of the sun. Over the next 1. 1 billion years, Solar luminosity will increase by 10% and over the next 3. 5 billion years by 40%. Earth's increasing surface temperature will accelerate the inorganic carbon cycle reducing CO2 concentration to levels lethally low for plants in approximately 100 to 900 million years. The lack of vegetation will result in the loss of oxygen in the atmosphere, Making animal life impossible. About a billion years from now, All surface water will have disappeared and the mean global temperature will reach 70 degrees Celsius. Earth is expected to be habitable until the end of photosynthesis about 500 million years from now, But if nitrogen is removed from the atmosphere, Life may continue until a runaway greenhouse effect occurs 2. 3 billion years from now. Anthropogenic emissions are probably insufficient to cause a runaway greenhouse at current solar luminosity. Even if the sun were eternal and stable, 27% of the water in the modern oceans will descend to the mantle in 1 billion years due to reduced steam venting from mid-ocean ridges. The sun will evolve to become a red giant in about 5 billion years. Models predict that the sun will expand roughly 1 AU, About 250 times its present radius. Earth's fate is less clear. As a red giant, The sun will lose roughly 30% of its mass, So, Without tidal effects, Earth will move to an orbit 1. 7 AU from the sun when the star reaches its maximum radius. Most if not all remaining life will be destroyed by the sun's increasing luminosity. A 2008 simulation indicates the Earth's orbit will eventually decay due to tidal effects and drag, Causing it to enter the sun's atmosphere and be vaporized. Physical Characteristics Shape. The shape of the Earth is nearly spherical. There is a small flattening at the poles and bulging around the equator due to Earth's rotation. To second order, Earth is approximately an oblate spheroid, Whose equatorial diameter is 43 km larger than the pole-to-pole diameter, Although the variation is less than 1% of the average radius of the Earth. The point on the surface farthest from the Earth's center of mass is the summit of the equatorial Chimborazo volcano in Ecuador. The average diameter of the reference spheroid is 12, 742 km. Local typography deviates from this idealized spheroid, Although on a global scale these deviations are small compared to the Earth's radius. The maximum deviation is only 0. 17% at the Mariana Trench, Whereas Mt. Everest represents a deviation of 0. 14%. In geodesy, The exact shape that Earth's oceans would adopt in the absence of land and perturbations, Such as tides and winds, Is called the geoid. More precisely, The geoid is the surface of gravitational equipotential at mean sea level. Chemical Composition Earth's mass is approximately 5. 97 x 1024 kg. It is composed mostly of iron 32. 1%, Oxygen 30. 1%, Silicon 15. 1%, Magnesium 13. 9%, Sulfur 2. 9%, Nickel 1. 8%, Calcium 1. 5%, And aluminum 1. 4%, With the remaining 1. 2% consisting of trace amounts of other elements. Due to mass segregation, The core region is estimated to be primarily composed of iron 88. 8%, With smaller amounts of nickel 5. 8%, Sulfur 4. 5%, And less than 1% trace elements. The most common rock constituents of the crust are nearly all oxides. Chlorine, Sulfur, And fluorine are the important exceptions to this, And their total amount in any rock is usually much less than 1%. Over 99% of the crust is composed of 11 oxides, Principally silica, Alumina, Iron oxides, Lime, Magnesium, Potash, And soda. Internal Structure Earth's interior, Like that of the other terrestrial planets, Is divided into layers by their chemical or physical properties. The outer layer is a chemically distinct silicate solid crust, Which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovicic discontinuity. The thickness of the crust varies from about 6 km under the oceans to 30-50 km for the continents. A crust and a cold rigid top of the upper mantle are collectively known as the lithosphere, And it is of the lithosphere that the tectonic plates are composed. Beneath the lithosphere is the asthenosphere, A relatively low viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 km below the surface, Spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, An extremely low viscosity liquid outer core lies above a solid inner core. Earth's inner core might rotate at a slightly higher angular velocity than the remainder of the planet, Advancing by 0. 1 to 0. 5 degrees per year. The radius of the inner core is about one-fifth of that of Earth. Heat Earth's internal heat comes from a combination of residual heat from planetary accretion – about 20% – and heat produced through radioactivity decay – 80%. The major heat-producing isotopes within Earth are potassium-40, Uranium-238, And thorium-232. At the center, The temperature may be up to 6000 degrees Celsius, And the pressure could reach 360 GPA. Because much of the heat is provided by radioactive decay, Scientists postulate that early in Earth's history, Before isotopes with short half-lives were depleted, Earth's heat production was much higher. At approximately 3G, Twice the present-day heat would have been produced, Increasing the rates of mantle convection and plate tectonics, And allowing the production of uncommon igneous rocks such as chromatiites that are rarely formed today. The mean heat loss from the Earth is 87 Mw, M to the negative 2, For a global heat loss of 4. 42 x 10 to the 13th W. A portion of the core's thermal energy is transported toward the crust by mantle plumes, A form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hot spots and flood basalts. More of the heat in the Earth is lost through plate tectonics, By mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, The majority of which occurs under the oceans, Because the crust there is much thinner than that of the continents. Surface The total surface area of Earth is about 510 million km2. Of this, 70. 8% or 361. 13 million km2 is below sea level and covered by ocean water. Below the ocean's surface are much of the continental shelf, Mountains, Volcanoes, Oceanic trenches, Submarine canyons, Oceanic plateaus, Abyssal plains, And a globe-spanning mid-ocean ridge system. The remaining 29. 2% or 148. 94 million km2 not covered by water has terrain that varies greatly from place to place, And consists of mountains, Deserts, Plains, Plateaus, And other landforms. Tectonics and erosion, Volcanic eruptions, Flooding, Weathering, Glaciation, The growth of coral reefs, And meteorite impacts are among the processes that constantly reshape Earth's surface over geological time. The continental crust consists of lower-density materials such as the igneous rocks granite and andesite. Less common is basalt, A denser volcanic rock that is the primary constituent of the ocean floors. Sedimentary rock is formed from the accumulation of sediment that becomes buried and compacted together. Nearly 75% of the continental surfaces are covered by sedimentary rocks, Although they form about 5% of the crust. The third form of rock material found on Earth is metamorphic rock, Which is created from the transformation of pre-existing rock types through high pressures, High temperatures, Or both. The most abundant silicate minerals on Earth's surface include quartz, Feldspars, Amphibole, Mica, Pyroxene, And olivine. Common carbonate minerals include calcite, Found in limestone, And dolomite. The elevation of the land's surface varies from the low point of negative 418 meters at the Dead Sea to a maximum altitude of 8, 848 meters at the top of Mount Everest. The mean height of land above sea level is about 797 meters. The pedosphere is the outermost layer of Earth's continental surface and is composed of soil and subject to soil formation processes. The total arable land is 10. 9% of the land's surface, With 1. 3% being permanent cropland. Close to 40% of Earth's land surface is used for agriculture, Or an estimated 16. 7 million kilometers squared of cropland and 33. 5 million kilometers squared of pastureland. Hydrosphere The abundance of water on Earth's surface is a unique feature that distinguishes the blue planet from other planets in the solar system. Earth's hydrosphere consists chiefly of the oceans, But technically includes all water surfaces in the world, Including inland seas, Lakes, Rivers, And underground waters down to a depth of 2, 000 meters. The deepest underwater location is Challenger Deep of the Mariana Trench in the Pacific Ocean, With a depth of 10, 911. 4 meters. The mass of the oceans is approximately 1. 35 x 10-18 metric tons, Or about 1. 44 hundredths of Earth's total mass. The oceans cover an area of 361. 8 million kilometers squared, With a mean depth of 3, 682 meters, Resulting in an estimated volume of 1. 332 billion kilometers cubed. If all of Earth's crustal surface were at the same elevation as a smooth sphere, The depth of the resulting world ocean would be 2. 7 to 2. 8 kilometers. About 97. 5% of the water is saline. The remaining 2. 5% is freshwater. Most freshwater, About 68. 7%, Is present as ice in ice caps and glaciers. The average salinity of Earth's oceans is about 35 grams of salt per kilogram of seawater. Most of this salt was released from volcanic activity or extracted from cool igneous rocks. The oceans are also a reservoir of dissolved atmospheric gases, Which are essential for the survival of many aquatic lifeforms. Atmosphere has an important influence on the world's climate, With the oceans acting as a large heat reservoir. Shifts in the oceanic temperature distribution can cause significant weather shifts, Such as the El Niño-Southern Oscillation. Atmosphere The atmospheric pressure of Earth's sea level averages 101. 325 kPa, With a scale height of about 8. 5 kilometers. A dry atmosphere is composed of 78. 084% nitrogen, 20. 946% oxygen, 0. 934% argon, And trace amounts of carbon dioxide and other gaseous molecules. Water vapor content varies between 0. 01% and 4%, But averages about 1%. The height of the troposphere varies with latitude, Ranging between 8 kilometers at the poles to 17 kilometers at the equator, With some variation resulting from weather and seasonal factors. Earth's biosphere has significantly altered its atmosphere. Atmospheric photosynthesis evolved 2. 7 GYA, Forming the primarily nitrogen-oxygen atmosphere of today. This change enabled the proliferation of aerobic organisms and, Indirectly, The formation of the ozone layer, Due to the subsequent conversion of atmospheric O2 into O3. The ozone layer blocks ultraviolet solar radiation, Permitting life on land. Other atmospheric functions important to life include transporting water vapor, Providing useful gases, Causing small meteors to burn up before they strike the surface, And moderating temperature. This last phenomenon is known as the greenhouse effect. Trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, Thereby raising the average temperature. Water vapor, Carbon dioxide, Methane, Nitrous oxide, And ozone are the primary greenhouse gases in the atmosphere. Without this heat retention effect, The average surface temperature would be negative 18 degrees Celsius, In contrast to the current 15 degrees Celsius, And life on Earth probably would not exist in its current form. In May 2017, Glints of light seen as twinkling from an orbiting satellite a million miles away were found to be reflected light from ice crystals in the atmosphere.