Density of the Earth
Written by Fraser Cain
The Earths interior (University of Chicago)
The density of the Earth is 5.51 grams per cubic centimeter. This is an average, of course. If you could mix up the Earth so all of its mass was evenly distributed, and then took a 1 cm cube and put it on the scale, it would weigh 5.51 grams. This makes Earth the densest planet in the Solar System.
Just for comparison, the density of water is 1 g/cm3, the density of rock is 2-3 g/cm3, and the density of iron is 7.87 g/cm3. So, the density of Earth is somewhere in between the density of rock and pure iron.
The surface of the Earth is mostly water and rock, so scientists have long suspected that our planet's high density comes from large quantities of iron in the core. This suspicion was confirmed in 1936 by seismologist Inge Lehmann, who was measuring how seismic waves passed through the Earth. He detected that waves bounced off the solid iron core of the Earth.
Earth is the densest planet in the Solar System, and tiny Mercury, at 5.43 g/cm3. One interesting fact is that Mercury would actually be more dense than Earth; however, our planet has much more mass, and so it compacts itself more tightly than Mercury. If Mercury and Earth were the same size, Mercury would be more dense.
Want to calculate the density of Earth for yourself? It's easy if you've got a calculator. Just divide the mass of Earth (5.97 x 1024 kg) by the volume (1.08 x 1012 km3). You're going to get a number that's in kilograms per cubic kilometer, so you'll need to do a little number converting.
We have written many articles about density for Universe Today. Here's an article about the density of the Sun, and here's one about the density of Mars.
Want more resources on the Earth? Here's a link to NASA's Human Spaceflight page, and here's NASA's Visible Earth.
We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.
Filed under: Astronomy
