# What is the mass of Earth's crust?

Mass of crust = 19.1 zetagrams (1.913x1022 kg).

It is not possible to give an exact answer to this question as the Earth's crust varies in thickness and in density. However it is possible to make an estimate, although this will contain errors due to the simplifying assumptions it will be necessary to make.

Earth's crust varies in thickness from as little as 2km thick to over 70 km thick with an average value of approximately 35 km for the continental crust and 4.5 km for the oceanic crust.

Approximately 70 % of Earth's surface is covered in ocean and so it is assumed that this is the proportion of the crust formed of the denser, but thinner oceanic crustal rocks whereas the remaining 30 % is assumed to be composed of the thicker but less dense continental crustal rocks.

Density: It is assumed that the continental crust has an average density of 2700 kg/m3 and the oceanic crust a density of 3000 kg/m3.

Diameter of Earth = 6360 km.

As such, based on the above assumptions an estimation of the mass of the crust can be made by:

Calculating the volume of crustal material:

Volume of Earth = 4/3 x Pi x (6360 x 1000)3

Volume of Earth = 1.07761x1021 m3

Volume of Earth excluding oceanic crust:

Volume = 4/3 x Pi x (6356 x 1000)3

Volume of Earth excluding oceanic crust = 1.07532x1021 m3

Volume of Earth excluding continental crust:

Volume = 4/3 x Pi x (6325 x 1000)3

Volume of Earth excluding continental crust = 1.05991x1021 m3

As such the average volume of continental crust equals:

Volume = (1.07761x1021 - 1.05991x1021)

Volume = 1.76929x1019 m3

As such the average volume of oceanic crust equals:

Volume = (1.07761x1021 - 1.07532x1021)

Volume = 2.28575x1018 m3

Mass = Density x Volume:

Mass of oceanic crust = 2.28575x1018 x 3000 x 0.7

Mass of oceanic crust = 4.8x1021 Kg

Mass of continental crust = 1.76929x1019 x 2700 x 0.3

Mass of continental crust = 1.433x1022 Kg

Sum of masses of continental and oceanic crust :

Mass of crust = 1.913x1022 kg.