What is the Earth's average density and Who was the first person to detennine the Earth's average density?

 What is the Earth's average density?

The Earth's average density is about 5.52 grams per cubic centimeter-the units most scientists (and everyone else in the world) use to measure the density. The density of water is about 1 gram per cubic centimeter; the density of rocks at the Earth's  surface (usually in the form of granite) is about 2.7 grams per cubic centimeter; the upper mantle's density (mostly considered to be composed of peridotite) is about 3.4 grams per cubic centimeter. Many scientists believe the density of rocks at the Earth's core is very high, which is why they believe the center of our planet is composed of dense iron.

Who was the first person to detennine the Earth's average density?

In 1798, English physicist Henry Cavendish (1731-1810) calculated the Earth's density, basing his idea on specific gravity, or a ratio of the Earth's density to that of water. Although his data was good, he still made an error in calculating the Earth's density to be 5.48. This may have been due to an omission error of one number. Though Cavendish was close, the accepted value today is 5.518.

   Contrary to popular belief, the famous "Cavendish experiment" (or "Cavendish apparatus") to determine the Earth's density was actually designed by the geologist Rev. John Michell, who is also known as the "father of seismology" to some. Five years after Michell's death, Cavendish rebuilt the apparatus to calculate the Earth's density, making it smaller than the original. Using two fixed lead spheres hanging from a metal rod, he measured the twisting in a silver wire that supported the spheres when exposed to masses of metal. This allowed him to find the attraction force on a mass the  size of the Earth-and eventually to determine the planet's density.