Lab - The petrographic characteristics of the Earth's crust and mantle

Soundtrack excerpt:
Plate tectonics: the story of a model (1-B)

Scientific problem:
In his theory of continental drift, A. WEGENER indicates the existence of distinct oceanic and continental domains.
Measurements of seismic wave propagation through the crust suggest different types of rocks in these domains.
Finally, the identification of the Moho as early as 1909 beneath the oceans and continents reflects a difference in composition between the crust and the mantle.
What are the characteristics of the rocks in the crust and mantle?

Procedure:
Students will determine the density of the rocks that make up the crust and mantle in order to explain the ocean-continent duality and the fact that the crust rests on the mantle.
They will then conduct a study of these same rocks:
- on a macroscopic scale (texture, minerals visible to the naked eye),
- then on a microscopic scale (texture, minerals identified in Unanalyzed Polarized Light and Analyzed Polarized Light) and will investigate the origin of density differences.