[13] About 90% of the mass of the Earth is composed of the iron–nickel alloy (95% iron) in the core (30%), and the silicon dioxides (c. 33%) and magnesium oxide (c. 27%) in the mantle and crust.

Early estimates on the mean density of the Earth were made by observing the slight deflection of a pendulum near a mountain, as in the Schiehallion experiment.

An expedition from 1737 to 1740 by Pierre Bouguer and Charles Marie de La Condamine attempted to determine the density of Earth by measuring the period of a pendulum (and therefore the strength of gravity) as a function of elevation.

[22] He suggested that the experiment would "do honour to the nation where it was made" and proposed Whernside in Yorkshire, or the Blencathra-Skiddaw massif in Cumberland as suitable targets.

The Royal Society formed the Committee of Attraction to consider the matter, appointing Maskelyne, Joseph Banks and Benjamin Franklin amongst its members.

After a lengthy search over the summer of 1773, Mason reported that the best candidate was Schiehallion, a peak in the central Scottish Highlands.

[23] The mountain stood in isolation from any nearby hills, which would reduce their gravitational influence, and its symmetrical east–west ridge would simplify the calculations.

Its steep northern and southern slopes would allow the experiment to be sited close to its centre of mass, maximising the deflection effect.

[26] Absolute figures for the mass of the Earth are cited only beginning in the second half of the 19th century, mostly in popular rather than expert literature.

In 1821, Francesco Carlini determined a density value of ρ = 4.39 g/cm3 through measurements made with pendulums in the Milan area.

On the other hand, George Biddell Airy sought to determine ρ by measuring the difference in the period of a pendulum between the surface and the bottom of a mine.

Later, in 1883, the experiments conducted by Robert von Sterneck (1839 to 1910) at different depths in mines of Saxony and Bohemia provided the average density values ρ between 5.0 and 6.3 g/cm3.

This led to the concept of isostasy, which limits the ability to accurately measure ρ, by either the deviation from vertical of a plumb line or using pendulums.

Despite the little chance of an accurate estimate of the average density of the Earth in this way, Thomas Corwin Mendenhall in 1880 realized a gravimetry experiment in Tokyo and at the top of Mount Fuji.

The Astronomical Almanach Online as of 2016 recommends a standard uncertainty of 1×10−4 for Earth mass, ME 5.9722(6)×1024 kg[2] Earth's mass is variable, subject to both gain and loss due to the accretion of in-falling material, including micrometeorites and cosmic dust and the loss of hydrogen and helium gas, respectively.

The combined effect is a net loss of material, estimated at 5.5×107 kg (5.4×104 long tons) per year.

The sum of material is estimated to be 37000 to 78000 tons annually,[34][35] although this can vary significantly; to take an extreme example, the Chicxulub impactor, with a midpoint mass estimate of 2.3×1017 kg,[36] added 900 million times that annual dustfall amount to the Earth's mass in a single event.

Mass loss due to the combination of nuclear fission and natural radioactive decay is estimated to amount to 16 tons per year.

[citation needed] An additional loss due to spacecraft on escape trajectories has been estimated at 65 tons per year since the mid-20th century.