[thedoc (OP)]

Lujain Alyamani  asked the Naked Scientists:
   
Hello!!

Ummm... I was wondering what would happen if the inner core of our earth was cold in other words frozen? Would this affect the Earths crust , if so how? Also what would happen if the outer core of our earth was soild? How would this affect earthquake waves? Also why can't S-waves pass through liquids?

Thank You..
Lujain

What do you think?

[CliffordK]

If the core was solid, we would likely have a much more geologically stable planet.  No earthquakes.  No volcanoes. 

The tectonically active planet has brought many minerals to the surface, without which the advancement of civilization would not have been possible.  On an extended timeframe, without tectonic activity, the mountains would erode, and potentially the world would eventually end up under the sea.

There would also be a weaker magnetic field, and more solar ionic particles and cosmic rays penetrating deeper into the atmosphere, potentially damaging life on the planet, and damaging our atmosphere.

[Bass]

p-waves, or compression waves, travel through liquid because liquids are compressible.  s-waves, or shear (secondary) waves, have motion at right angles to the direction of propagation; which means they depend on the rigidity of the body for their transmission.  Since liquid has no (or very little) rigidity, and therefore doesn't shear, s-waves can't travel through them. (It's actually a bit more complicated, but that's the basic explanation).

[evan_au]

If the inner earth were cold, there would be no volcanoes, but also no uplift of land or subduction and recycling of ocean sediments.

Eventually all of the mountains and islands would erode and be deposited on the seafloor, leaving a waterworld. 

I hope you can swim.

[evan_au]

Expanding on the atmospheric damage:
Earth's magnetic field is driven by the heat of the core, and provides a strong magnetic field extending thousands of miles/km into space. This slows down and diverts the solar wind particles into the polar regions (where it is visible as the aurora), encapsulating and containing the earth's ionosphere.

Without this, the solar wind would tear away at our atmosphere - this is what is thought to have happened on Mars: http://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ 

[Bill S]

If the inner earth were cold, there would be no volcanoes, but also no uplift of land or subduction and recycling of ocean sediments.

Wouldn't some tectonic movement be possible as a result of heat generated by nuclear decay within the mantle?  It is my understanding that current thinking has this as the major cause of mantle convection.  Is that correct?

[Bored chemist]

Since the question asks what would happen if the core were cold then there couldn't be a hot mantle.
It could only happen if there were no radioactive elements decaying.

[damocles]

In one sense that is right BC, in another it is quite wrong.
If we imagine that some omnipotent being came along and snap froze the whole Earth to liquid nitrogen temperature, then the first thing that would happen would be that the mantle and the crust would start to get warm, because uranium and thorium are lithophiles that are concentrated in the crust and mantle, and almost completely absent from the siderophile core. The core would later become hot, but only as the result of heat conduction from the mantle.
But there is no possible mechanism for planetary formation or evolution that could result in an Earth-like planet achieving a uniform temperature around that of liquid nitrogen -- or even of liquid water, for that matter.
Mind you I have heard of Ganymede and Callisto, two of the very large satellites of Jupiter, being described as "frozen muddy puddles".