Why do the continents "float high" relative to the ocean basins? Question #6 - How does one determine the relative ages of a sequence of sedimentary rocks? Absolute ages? Question #9 - Define the term rock. How many major classes of rocks are there, and what are they? Chapter 3 Question #1 - What is the lithosphere, and what are the three major boundaries of lithospheric plates? Question #3 - Why is it difficult to subduct the continental crust of earth? Questions #7 - How do the processes of weathering and erosion relate to the formation of soils and sedimentary rocks?