Nuclear freeze

  1. What would the surface temperature range of the Earth be presently, without having had the nuclear reactions at its core?
     
  2. jcsd
    Earth sciences news on Phys.org
  3. sylas

    sylas 1,745
    Science Advisor

    About the same as it is now.

    Here is a more detailed answer. You ask a very good question; which relates to a dispute over how long it would take for the Earth to cool from a molten state to its present state. The question received a lot of attention around the end of the nineteenth century, when Kelvin estimated that the Earth could be only around about 25 million years old; which was far too young to encompass what was being discovered about gradual processes in geology and biology for developing the features seen on the Earth.

    The solution to the dilemma was radioactivity, discovered at the turn of the century. This meant heat was being continually generated within the Earth, and calculations based on a cooling sphere did not apply.

    But the data used for estimating cooling of the Earth was not a surface temperature. It was the temperature gradient within the Earth. The surface temperature is determined almost entirely by how solar radiation interacts at the surface; with the effect of geothermal heat being quite negligible. Without the nuclear reactions at the core, the whole Earth would have long ago cooled down to be something similar to the surface temperature. As it is, the interior of the Earth remains very hot, with a strong temperature gradient.

    Mathematical details of Kelvin's famous argument can be found at Lord Kelvin and the Age of the Earth, a paper used within a mathematical unit at the University of Rochester, NY, USA.

    Felicitations -- sylas
     
    Last edited: Oct 27, 2009
  4. Is the core of the earth hot due to nuclear reactions or due to extreme pressure or both?

    Or did you mean nuclear in a different sense?
     
  5. sylas

    sylas 1,745
    Science Advisor

    The heat of the Earth's core is maintained by nuclear reactions, not pressure. Specifically, the decay of radioactive nuclei.

    Cheers -- sylas
     
  6. Borek

    Staff: Mentor

    Pressure doesn't have to go together with high temperature. Squeeze something, let it cool down - and you have high pressure and low temperature.
     
  7. Cool, I didn't know that.
     
  8. The heat of the earths interior is primarily from the decay of radioactive isotopes and residual heat from original formation. As Sylas pointed out, the temperature of the surface of the earth is not influenced significantly by the interior temperature. This is because earths crust is so thick and such a poor conductor of heat, that very little of it escapes to the surface.

    However, the interior temperature does influence plate tectonics and the magnetic field.
    Billions of years ago, when the earths interior was significantly warmer than it is now, the continental plates moved much faster.
     
  9. Eventually, as earths interior cools off and the continental plates ceases to move, this will result in less volcanic activity, less atmospheric CO2, less greenhouse affect and a cooler surface temperature. However, this is over billions of year.
     
  10. Thats incouraging. If global warming kill everything on the surface of the planet, the core will eventually right everything : )
     
  11. sylas

    sylas 1,745
    Science Advisor

    Actually, as pointed out in the start, what goes on in the core and the mantle has pretty much no effect on surface temperature. The surface temperature is determined by interactions with the Sun. The interior temperature is high because heat leaks out very slowly.

    Felicitations -- sylas
     
  12. I was just joking, but I understand what you mean.
     
  13. sylas

    sylas 1,745
    Science Advisor

    I thought so, and in fact I nearly added a comment in my post to say so. In fact, it was there, but I removed it before posting, just for the sake of keeping my post short and simple. We often readers dropping in who may not be up on all the details and who do get a tad confused. I did not really think you were confused on this point yourself.

    Best wishes -- sylas
     
  14. Of course it depends on the time frame.

    Big differance between a lifetime and 10 billion years.
     
  15. The 0.09 W/m or so of geothermal warmth has no significant direct effect. There are likely to be significant indirect effects. If there are no more vulcanoes, that could lower CO2 after millions of years, lowering the temperature. If you wait longer the continents will all end up in the oceans, because of erosion. That's likely to have an effect on temperature as well, altough I wouldn't know what it is.
     
  16. Well maybe we could speculate a bit more, if we consider how the Earth is build up as a set of gyroscopes, with a solid inner core a fluid outer core and a ductile mantle. None is perfectly spherical which makes that they are precessing slowly under the gravity of sun and moon. Each gyro with its own unique parameters so each is precessing at different rates.

    This means that the alignment of the spin axes of core and mantle is not automatically rigid as they tend to loose alignment due to the precession. If the spinning is oblique, this will generate a lot of internal drag in the fluid inner core, like the fluid torque converter in an automatic gear box. James Vanyo has attempted to quantify these effects here, see both papers.

    However it looks that a part of the spinning energy of the Earth is converted into heat in the Earth core, which should also contribute somewhat to the heat of inner Earth.
     
  17. sylas

    sylas 1,745
    Science Advisor

    Yes, there are large indirect effects. Climate long term is drastically impacted by plate tectonics and geological processes, in establishing the conditions of atmosphere, ocean and topography which all help determine the Earth's energy balance.
     
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