Option T5: GEOLOGY OF THE LITHOSPHERE Key Idea 1: The heat loss leads to cooling and the Earth’s development of a strong outer shell (lithosphere) underlain by a layer of lower strength (asthenosphere) Knowledge and Geological techniques Comments understanding and skills a. The Earth loses heat Graphical comparison of Candidates should be through its surface, continental and oceanic aware that the strength of leading to the formation geotherms with the mantle materials depends upon of a cold, rigid outer layer solidus curve to explain temperature which changes known as the lithosphere: lithosphere/asthenosphere with depth (pressure). surface heat flow and distinction. Approximately 99% of temperature variation internal heat loss at Earth’s with depth, rock strength the surface is by related to temperature. conduction through the crust, with mantle convection the dominant method of heat transport from deep within the Earth. b. The base of the Candidates will be lithosphere is defined as expected to analyse data in the 1300 isotherm; a variety of forms to oC lithospheric thickness demonstrate that the differs between oceanic lithosphere is continents and oceans. typically between 50-140 km thick (but beneath the mid-ocean ridges can be only 1- 2km), while continental lithosphere ranges in thickness from 40 km to about 150 km, though even deeper under cratons. c. Global seismology Ray path modelling to show provides evidence for the refraction of earthquake body distinction between waves through low velocity lithosphere and zone. asthenosphere: seismic low velocity zone in Interpretation of P- and S- upper mantle. wave velocity-depth curves and identification of low velocity zone.
Option T5: GEOLOGY OF THE LITHOSPHERE Key Idea 1: The Earth’s heat loss leads to cooling and the development of a strong outer shell (lithosphere) underlain by a layer of lower strength (asthenosphere) Knowledge and understanding Geological techniques and skills Comments a. The Earth loses heat through its surface, leading to the formation of a cold, rigid outer layer known as the lithosphere: surface heat flow and temperature variation with depth, rock strength related to temperature. Graphical comparison of continental and oceanic geotherms with the mantle solidus curve to explain lithosphere/asthenosphere distinction. Candidates should be aware that the strength of materials depends upon temperature which changes with depth (pressure). Approximately 99% of Earth’s internal heat loss at the surface is by conduction through the crust, with mantle convection the dominant method of heat transport from deep within the Earth. b. The base of the lithosphere is defined as the 1300 oC isotherm; lithospheric thickness differs between continents and oceans. Candidates will be expected to analyse data in a variety of forms to demonstrate that the oceanic lithosphere is typically between 50-140 km thick (but beneath the mid-ocean ridges can be only 1- 2km), while continental lithosphere ranges in thickness from 40 km to about 150 km, though even deeper under cratons. c. Global seismology provides evidence for the distinction between lithosphere and asthenosphere: seismic low velocity zone in upper mantle. Ray path modelling to show refraction of earthquake body waves through low velocity zone. Interpretation of P- and S- wave velocity-depth curves and identification of low velocity zone.
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