12_Earth - GEL36 SOLAR SYSTEM Lecture 12 Earth(Ch 20 Goal...

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1 GEL36 SOLAR SYSTEM Lecture 12: “Earth” (Ch. 20) Goal of the Lecture: To view the Earth as the unique planet that it is and to use our understanding of the Earth as a model to compare with the other terrestrial planets, our moon, and the moons of the Jovian planets. Earth as a unique planet in our solar system There are two features on Earth that make it a truly unique planet in the solar system: 1) liquid water covers more than 70% of the Earth’s surface, and 2) life exists in countless forms (including humans who are capable of physically altering the planet). We all know the Earth’s period of rotation is once every 24 hours and the orbital period is 365 days. We know the Earth’s axis is tilted at 23.5° and it’s this tilt that gives the Earth its change of seasons. Interior of the Earth You all realize that the Earth, having differentiated early in its history like the rest of the planets, is composed of an interior core, a thick mantle and thin, outer crust. * Pressure increases constantly with depth in the Earth because of compression caused by the weight of overlying rock. And as pressure increases toward the center of the Earth, the density of rock increases also. Plus, the transition to a core made of iron increases the density. Temperature also increases toward the interior of Earth as a result of compression of rock and metal as well as the deep interior being the source of accretionary heat and radioactive heat. - these characteristics are the same for all planetary bodies (as well as stars) Inner core is solid, outer core is liquid, both composed of very hot (~6000 K), very dense (~10-14 g/cc), metallic iron and small amounts of nickel. The solid inner core is “almost pure crystalline iron almost as hot as the surface of the sun but “frozen” at the center of the planet by the intense pressure”. About the size of our moon. The liquid outer core is a “dense sea of molten iron with traces of other metals”
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2 Mantle composed of dense (3.5 to 5.8 g/cc) silicate rock and metal oxides. - comprises 2/3rds of the mass of the Earth - mantle rock is a solid that acts like a very thick liquid - it behaves like a plastic that flows under pressure. Crust is relatively thin (up to 60 km under continents and 10 km under oceans) and has the lowest density (2.5 to 3.5 g/cc). It is composed of mostly silicate rock that acts as a brittle material (it cracks rather than flows). But we’ve obviously never been very far into the Earth’s interior, (the deepest we’ve ever drilled is about 12 km down, only 0.2% of the way to the core) . . . . How do we know the thicknesses and compositions of the Earth's interior so specifically? Seismology - the study of earthquake waves that can be analyzed to discern the interior dimensions and compositions of the Earth (or any planet for that matter). Earthquakes occur along faults when stresses build to a threshold that exceeds the
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This note was uploaded on 05/31/2011 for the course GEL 36 taught by Professor Osleger,d during the Spring '08 term at UC Davis.

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12_Earth - GEL36 SOLAR SYSTEM Lecture 12 Earth(Ch 20 Goal...

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