The Scientific Mysteries of Earth's Inner Core

I often look outward on this channel into interstellar space to find the strange and interesting scientific developments I talk about. But our own world is, in many ways, still largely a mystery. Earth-bound scientific mysteries can be found everywhere from the ice caps to the oceans but one area stands out for our lack of understanding of it. That's earth's hellish inner core, and just last week it seems that one of its great mysteries has finally been solved. More on that in a minute.

Earth's inner core is a 760 mile wide solid ball, kept solid by the intense pressure of the environment. And it's hot, to the tune of 5700 degrees Kelvin. It's also, unsurprisingly, mostly made up of an iron-nickel alloy in much the same way that asteroid cores and iron meteorites are. We've known about it for a while, the solid inner core that is separate from the liquid molten outer core was deduced in 1936 by Danish seismologist Inge Lehmann while studying seismographs of earthquakes originating on the other side of the globe.

Another interesting aspect of the inner core is that it's growing. As the earth cools, the inner core solidifies about half a millimeter per year of the molten outer core. And it seems to spin faster than the rest of the planet since it's essentially floating in liquid. The growth of the inner core is an important process in creating the convection in the liquid outer core that is the origin of the earth's magnetic field. Without that magnetic field, there would be no life on earth so a convecting core is key to any earth-like planet's ability to evolve complex life.

But the inner core is also younger than the age of the earth, considerably so and probably younger than the evolution of life itself on earth suggesting that the way earth's magnetic fields are generated has changed. It only began to solidify between .5 and 1.5 billion years ago. It also may not be a single solid mass, though this is not yet definitively known, but may instead be made up of two layers and that the innermost layer might be rotated on its side. It's unclear just what caused that, but whatever it was it had to be substantial and there is an odd possible correlation here with something else.

People who study the palaeomagnetic field using evidence preserved in ancient rocks believe that the earth's magnetic field switched axes about .5 billion years ago. This in turn may have something to do with the so-called "Cambrian explosion" that occurred at about the same time when evolution underwent a massive speed up. We don't know for sure, but changes in earth's magnetic field might have been responsible for allowing the evolution of increasingly complex life on earth.

But now to the solved mystery. We've always been able to infer that earth's core is about 95 percent iron and nickel. The density of the inner core suggests though that the remaining five percent must be made up of counter intuitively light elements. It's always been assumed that it was sulfur, oxygen or silicon. But a Japanese research team lead by Dr. Eiji Ohtani seems to have solved the mystery.  Using lab experiments employing high temperatures and pressures present in the inner core, they matched various mixes of materials until they found one that matched seismic data. As it turns out, it seems to be mostly silicon.

What's noteworthy here is that it's not oxygen. If it had been, it would mean that earth's surface was oxygen poor early on. But it also doesn't necessarily mean that it was oxygen rich. There are still a lot of unknowns there, but they should have deep implications on our models of how life arose on earth.

Thanks for listening. I am futurist and science fiction author John Michael Godier, currently with an upcoming book. It's called Supermind and raises deep questions about existence, reality and the course of the future and be sure to check out my other books at your favorite online book retailer and subscribe to my channel for regular, in-depth explorations into the interesting, weird and unknown aspects of this amazing universe in which we live.