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.
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