Planet Earth is a bit of a softie at heart

摘要

Our planet has a heart of iron, but it's not as tough as we thought. Earth's molten outer core and solid inner core are made mostly of iron, with a touch of nickel. To probe the inner core's properties, Arianna Gleason of Stanford University in California and colleagues subjected a piece of iron foil to pressures of about 200 gigapascals. That's 2 million times atmospheric pressure, but still lower than in Earth's centre. The researchers measured the speed at which deforming waves travel in the foil, and its density, from which they calculated the iron's strength. They then extrapolated this result to conditions in Earth's core (Nature Geoscience, doi.org/mhg). "Iron is actually weaker than expected under these extreme pressures and temperatures," says Gleason.