The earths biosphere consists of earths crust oceans

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The Earth’s BiosphereConsists of Earth’s crust, oceans, lower atmosphere thin!Fragile (We live in a delicate balance with nature)oIn cosmic time, our favorable ecosystem is transient and evolving rapidlyFor example: Earth's surface is only temporary.oAlthough the rapidly growing human population is having deleterious effects on the biosphere, these are probably survivable (even if the costs could be catastrophic). The most serious, long-term threats to the ecosystem are extraterrestrialand beyond immediate human control: asteroid/comet impacts, solar evolution, supernovae and other stellar explosions, etc.oAstronomy is the ultimate ecology.The Age of the EarthSedimentation rate/geological strata methodoDeveloped in 19th centuryoMakes use of relatively uniform rate of sediment deposit on ocean floors over long periods to estimate age of strata. oLess precise; gives relative valuesRadioisotope dating methodoBased on well-determined decay rates of naturally occurring radioactive isotopes. E.g. uranium ==> lead. Much more precise than stratiography. Thoroughly understood on the basis of quantum mechanics.o"Half life" = time it takes for half of original sample of unstable isotope to decay to "daughter" isotope. Half lives for unstable isotopes range from
microseconds to billions of years.oEstimate age from ratio of parent to daughterResultso===> oldest Earth surface rocks 3.9 billion yearso===> Moon,meteorites 4.6 billion yearsThe Earth’s InteriorEarth's mass is determined from the orbit of the Moon or of artificial spacecraft by applying Kepler's 3rd law.Mass/Volume = density, a clue to compositionoEarth 5.5 grams/cc ==> heavy elements (like Fe)oJupiter 1.3 grams/cc ==> light elements (H,He)Probe interior with seismic wavesfrom earthquakesoThese show that the interior is differentiated: i.e. composition, density change with depthoCore (innermost), mantle (body), crust (outermost)oDensities range from 12 grams/cc in the core to 3 grams/cc in the crust, implying that the core contains more heavy elements than the crust.oTemperature at the core is over 5000 K.The differentiation implies that Earth's interior was once molten, so that heavier materials could settle to the center.oInitial heat source: impactsof in-falling planetesimals during formation stagesoContinuing interior heat source: radioactive decayof uranium and other materials: even though a small fraction of the Earth's makeup, the heat generated escapes only slowly.“Plate Tectonics”A new (1950's - 60's) "paradigm" for the origin of geological structuresThe outer layers of the Earth (the crust and the upper mantle, together called the lithosphere) are thin and crackedinto pieces called "plates"These float on partially melted, plastic material (the asthenosphere) below them.

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