What’s with Earth’s Inner Core? A New Research Paper Shows Evidence Its Spin Rate is Slowing

In today’s Washington Post, an article by Carolyn Johnson reports that new research shows Earth’s inner core is changing its rate of spin. As inner core stories go, I’m not sure this one lives up to science fiction films where the centre of the Earth is featured. From Jules Verne’s Journey to the Centre of the Earth first published in 1864, to today’s article, trying to understand what lies beneath our feet is of fascination to many. It has spawned movies like 2003’s, The Core and 2009’s, 2012 as well as two versions of Jules Verne’s story, with science fiction authors and scriptwriters speculating about the mysterious molten ball of iron sitting deep inside the planet.

What we do know for certain is that the iron core influences an important safety feature of our planet, Earth’s magnetic field. Some five thousand kilometres (3,000 miles) beneath the surface, the core is solid iron floating in a liquid outer core with the latter in constant motion. It is this motion that generates the planet’s magnetic field and the magnetosphere that protects all life on Earth from harmful solar and cosmic radiation.

In today’s Washington Post article, Johnson describes a multi-decade study recently published in Nature Geoscience that describes how Earth’s core dynamics are changing speculating on whether this is caused by multidecadal periodicity.

In other words, the spin rate of the core may be speeding up and then slowing down. Evidence shows that up until 2009 the core spin rate was faster than the Earth’s 24-hour day. In 2009 it was in synch. And now it is slower. Based on seismological observations the research described suggests a 70-year cycle of speeding up and then slowing down.

The study is from a team of geoscientists at Peking University led by Xiaodong Song who was the first to provide evidence that the core’s rate of spin was not necessarily in synch with the 24-hour spin cycle we experience daily. The data used to come to this conclusion came from seismic records going back to 1964.

Seismic events happen every day here on Earth. We just only hear about the big ones like earthquakes that topple buildings and spawn tsunamis or Earth movement from volcanic eruptions. But daily, seismologists record the shaking of the planet. The waves generated by these events pass through the planet’s inner core and are measurably producing a temporal map to help describe the dynamic environment of the core deep within the Earth.

All though it seems that we live on a very stable motionless surface unless we create the motion, the truth is, there are so many moving parts around us. The Earth is rotating. The inner core is rotating. The Moon which exerts a gravitational pull on the Earth rotates around us. Earth rotates around the Sun while it spins around the Milky Way’s central core. Nothing in our environment isn’t in motion.

To all of these external moving parts, we can now add angular momentum from deep inside the planet that is linked to changes to Earth’s day. Just in case you didn’t know it, that 24-hour day hasn’t been with us forever and appears to be growing in length. In fact, if you were to reverse the planet’s time clock you get the following:

• a day 4.5 billion years ago was 4 hours long.
• It was 12 hours long when life first emerged 3.5 billion years ago.
• Photosynthesis evolved 2.5 billion years ago when an Earth day was 18 hours long.
• The first eukaryotic cells (cells with nuclei) appeared 1.7 billion years ago when a day was 21 hours.
• Multicellular life arrived 1.2 billion years ago when a day lasted 23 hours.
• And our ancestors first appeared on the plains of Africa when the day began to approximate what exists today.

One wonders if the core has also been spinning down similarly throughout our planet’s history acting as one of Earth’s rotational brakes.