Question

Plate tectonicsA simple model (see figure below) considers a continent as a block(density ≈2800kg/m3)floating in the m...


Plate tectonicsA simple model (see figure below) considers a continent as a block(density ≈2800kg/m3)floating in the mantle rock around it(density ≈3300kg/m3).Assuming the continent is 35 km thick (the average thickness of the Earth’s continental crust), estimate the height of the continent above the surrounding mantle rock.

 

Answer

Airy's Hypothesis was given by Sir George Biddell Airy, who was an English mathematician and astronomer. He assumed that the crustal density is uniform.  Airy's Hypothesis explains that the Earth's crust floats over a substratum in a liquid state and has high density.

According to the question,

The density of the mantle (ρm) = 3300kg/cubic meters.

The density of the crust (ρc) =2800kg/cubic meters

The crustal thickness (t) = 35km or 35000 meters.

The relation gives the relation between the crustal root (r) and the height and thickness of the crust is given as, r=h+t

So, r=h+35000meters

Earth Science homework question answer, step 2, image 1

From Airy's Hypothesis formula,

r=h×ρcρm-ρch+35000=h×28003300-2800h+35000=h×2800500500h+17500000=2800h175000002300=hh=7608.696mh=7.6km

So, the height of the continent above the surrounding mantle rock is 7.6km

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