(a) The mass of the Earth has been determined as 5.973 7 × 10²⁴ kg. Calculate the Earth’s bulk (i.e. mean) density. You should assume the Earth is a sphere with a radius of 6371 km. Quote your answer to 3 significant figures.

(b) Examination of the composition of rocks comprising Earth’s continental crust and ocean floor crust gives a bulk density of 2.7 × 10³ kg m⁻³ and 3.0 × 10³ kg m⁻³, respectively, whilst that of the densest rocks (i.e. xenoliths brought up from depths of up to 100 km) is about 3.5 × 10³ kg m⁻³. How do these densities compare with Earth’s bulk density, and what does your result from (a) Suggest about density variation with depth?