First of its kind experiment uses diamond anvils to simulate the Earth`s core
(PHYSorg.com Physics)

In an effort to investigate conditions found at the Earth`s molten outer core, researchers successfully determined the density of liquid iron and the speed at which sound propagates through it at extremely high pressures. They achieved this with use of a highly specialized diamond anvil that compresses samples, and sophisticated X-ray measurements. Their findings confirm the molten outer core is less dense than liquid iron, and also put values on the discrepancy.