A high concentration of carbon within Earth’s inner core could explain a long-standing mystery about how the deepest part of our planet froze solid – a process that kick-started the magnetic field protecting life on the surface.
Earth’s inner core presents a paradox for geophysicists: it first formed as a massive liquid ball of mostly iron, then began to solidify within the last billion years. For that freezing process to start in a pure iron object, it would have had to cool by at least 700 kelvin in that time period, which seems impossibly fast given how big the inner core is.
Alfred Wilson and his colleagues at the University of Leeds,UK, have tackled this “inner core nucleation paradox” by simulating how the cooling of the inner core would change using a more realistic composition of elements than pure iron alone. The inner core is thought to consist primarily of an iron-nickel alloy, containing up to 10% nickel, but around 10 per cent is made up of an unknown composition of light elements like silicon, sulphur, oxygen and carbon.
The researchers used a supercomputer to simulate the interactions of iron and carbon atoms under the high pressure and temperature conditions of the inner core. With carbon atoms making up about 15 per cent of the non-iron and nickel mix, solid clusters of atoms started to form with as little as 250 K of cooling, a plausible temperature change for the inner core to undergo in roughly a billion years, says Wilson.
Wilson says that a more complex simulation – including oxygen – might reveal a scenario where the inner core could freeze with even less cooling.
This story is based on an article in New Scientist. The original research was published in EarthArXiv.
Bill Gray