The Earth’s Crust
The Crust and Plate Tectonics The crust is the outer rock zone of Earth. The crust appears to be rigid, stable; but it is not. The crust is constantly changing. Some evidence is directly observable – weathering and erosion. Earthquakes and volcanoes provide more dramatic evidence of change. Much evidence is indirect, incomplete – difficult to evaluate. Tectonics is the study of movement of Earth’s crust.
Ring of Fire Lab
Earthquake and Volcano Distribution Most earthquakes and volcanoes are concentrated in narrow geographic belts
Circum-Pacific Belt The most important concentration of earthquakes and volcanoes is the circum-Pacific belt (ring of fire). A smaller concentration is found in the Mediterranean-Himalayan Belt. Many other earthquakes occur along mid-ocean ridges and ocean trenches.
Earth’s Interior Seismic data indicates that there are three distinct solid zones and a liquid zone within Earth. The solid zones are the crust, mantle and inner core. The liquid zone is the outer core. These zones have been identified by measuring the changes in seismic waves as they move through Earth.
Lithosphere and Asthenosphere The crust and top of the mantle are similar in composition – they make up the lithosphere (100 km thick). Under the lithosphere is the upper mantle – the asthenosphere. The asthenosphere behaves like a thick, plastic fluid. The mantle is much more rigid under the asthenosphere.
The composition, density, temperature, and pressure of Earth’s crust and interior What is the density of the continental crust? What is the pressure at the center of Earth? What is the depth to the boundary of the outer core and the inner core? State the density of the oceanic plate.
When the density of rock is 5.0 g/cc, What layer of the earth’s interior is it? What is the pressure, in atmospheres? What is the depth, in km? When the interior temperature is 2000C, what is the approximate pressure, in atm? What layer of the earth is it?
Interior Composition Studies of seismic wave patterns (and some meteorites) infer that Earth’s core is composed of mainly high density Fe and Ni. The mantle (80% of Earth’s volume) is rock that is rich in Fe and Mg. It appears that Earth’s core is composed of iron under high pressure, with densities around 10 g/cc. This would allow the overall density of Earth to be 5.5 g/cc.