Question

Question #0703f

Answer 1

`\delta_{"cc"} = (\frac{\rho_{oc}}{\rho_{"cc"}}).\delta_{oc} = \frac{3\quadg.cm^{-3}}{2.7\quad g.cm^{-3}}\times 4\quad km = 4.4\quadkm`

Explanation:

Consider an area `A` and measure the crustal mass within that area. If the crustal thickness is `\delta`, then the crustal volume within this area is `A.\delta`

Mass of oceanic crust: `\quad M_{oc} = \rho_{oc}.A.\delta_{oc}`......(1)
Mass of continental crust: `\quad M_{"cc"}=\rho_{"cc"}.A.\delta_{"cc"}` ...... (2)

To have the same crustal mass (i.e `M_{oc}=M_{"cc"}`)

`\rho_{oc}.cancel{A}.delta_{oc} = \rho_{"cc"}cancel{A}.\delta_{"cc"}`
`\delta_{"cc"} = (\frac{\rho_{oc}}{\rho_{"cc"}}).\delta_{oc} = \frac{3\quadg.cm^{-3}}{2.7\quad g.cm^{-3}}\times 4\quad km = 4.4\quadkm`