8 ms·

Earth's core far hotter than thought

54 points by groundCode 13y ago

tocomment 13y ago
It's a shame there's no good way to harness that.
- ovis 13y ago
  Although it's admittedly difficult when the higher temperatures are hundreds or thousands of kilometers away, geothermal power plants do in fact harness that.
  - dkhenry 13y ago
    If I am not mistaken Iceland uses geothermal to a large extent and is very successful in doing so.
    - mtviewdave 13y ago
      Northern California, as well: http://en.wikipedia.org/wiki/The_Geysers http://en.wikipedia.org/wiki/The_Geysers
  - comicjk 13y ago
    Yes, we could use more research in the technical side of that. Right now hard-rock drilling is so expensive that geothermal is only viable where natural circulation of underground water brings heat up from hotter regions.
- blueprint 13y ago
  It's important to note the fact that the heat in the core does not exist in isolation of other fields. The Earth is a dynamo system, and the energy in the core is connected to the planet's magnetic field, the energy bound up in its orbit around the sun, and its gravitational field.
- 3am 13y ago
  Its rotation produces the magnetic field which keeps the solar wind from stripping away our atmosphere and leaving the Earth a dead planet like Mars. We're getting our money's worth.
aashaykumar92 13y ago
This article is fascinating but as someone who doesn't know much about this discipline, I'm hoping for someone to clarify my confusion: In the article, it states that our core has temperatures comprable to that of the sun. However, the sun is 93 million miles away while our core seems to only be approximately 4000 miles deep. Shouldn't the Earth be hotter than or are there just so many layers that the heat decreases at such a fast rate as it approaches the surface?
- blueprint 13y ago
  They're comparing the heat of Earth's core to the surface of the sun, not the core of the sun.
- ovis 13y ago
  The sun heats the earth surface through radiative heating, while the core is well insulated by the mantle and crust. Although they may have similar temperatures, the power output of the sun is certainly larger.
  - jasallen 13y ago
    To provide some further context to ovis' (correct) statements, none of our 'heat', or other energy from the sun comes in the form of conduction. It comes in the form of radiation (light, et al) which the sun has in huge, massive, ginormous quantities. In pop culture, we often talk about the heat of the sun as if it's a direct indicator for the amount of power therein, and the amount of power output. But while it's quite hot, its also quite busy showering us with other forms of energy.
- Jabbles 13y ago
  I'm afraid there are many things wrong with your model of how heat works. However a simple factor is that the surface of the sun is ~10000 times larger than the surface of the earth.
- monsterix 13y ago
  > In the article, it states that our core has temperatures comprable to that of the sun. However, the sun is 93 million miles away while our core seems to only be approximately 4000 miles deep. I was thinking you were about to ask why in the universe are we not able to measure the temperature of earth core that's only 4000 miles away from us and yet we claim to know the temperature of something that 93 million miles away... :)
bttf 13y ago
Was anyone else led by the title of this post to contemplate the difference in heat between thought and the Earth's core?
bcbrown 13y ago
So the previous estimate was 5000 C, and now it's 6000C +/- 500C, and that's "far hotter"? That doesn't seem like a huge adjustment to me.
- ecto 13y ago
  Perhaps a ~17% change is not significant on the scale that we inhabit (20C today depending where you are), but 1000C is a lot of degrees.
  - jlgreco 13y ago
    Indeed. It seems this new estimate puts it into "surface of the sun" territory (5700-8800K).
    - samstave 13y ago
      I know nothing about this, but I wonder if core temp would have any impact on the habitability of a planet. We know there is the habitable zone around a star, I wonder if that body in that zone would also need a certain core temp to support life.
      - jlgreco 13y ago
        I don't know much about this, but my understanding is that a hot core is not itself something that life particularly needs. The effects of that hot core however (Spinning core to make a magnetosphere? Volcanic activity changing atmospheric chemistry?) are probably more important. On the other hand, a hot core gives you deep sea thermal vents. Although I think the current prevailing theories don't have life originating near those on Earth, a hot core is certainly essential to life down there and, perhaps on another world, life could originate there.
edwinkite 13y ago
Geologist here. Earth's thermal evolution is unsolved decades after we figured out the stars. The Sun's temperature adjusts to energy production and loss on a 10^6 yr timescale (scaling as the time for a photon to diffuse from the heart of the Sun to the cold surface): << the Sun's age. The Earth's temperature adjusts to internal energy production and surface losses on a billion year timescale: of order the Earth's age. Planets have long memories and history matters. The Sun is reasonably well-mixed. Surface spectroscopy probes the make-up of the whole star. Earth is less well-stirred. Seismic imaging of the deep earth maps the edges of vast pods of material, radioactivity unknown, composition unknown (but definitely distinct from the near-surface stuff), age unconstrained but plausibly as old as the planet [1]. Structure and composition matter [2]. It's a hard problem. But it matters. When you look up at the night sky far from cities, for every star you see there's a habitable-zone Earth-radius planet that's closer [3]. We didn't know that six months ago. We think (for good, but circumstantial reasons) that complex life requires volcano-tectonic resurfacing - necessarily, a hot interior. Given that habitable-zone Earth-radius planets are not in short supply, the difference between fast and slow cooling for planets like Earth is the difference between a Galaxy where most every star system is habitable and one where almost all the planets are cinders. The core-mantle boundary heat flux Q_CMB estimated in this paper constrains the mantle energy balance d(E_mantle)/dt ~ Q_CMB - Q_surf + H_radioactive Surface heat flux Q_surf is ~46 terawatts. Mantle radioactivity H_radioactive is not well constrained but about 10 terawatts [2]. The implication is that despite the high core heat flux, Earth's mantle is cooling fast - maybe 100 microkelvins per century. Volcanism will therefore shut down in much less time than the remaining main sequence lifetime of the Sun. Absent human intervention, the reddening of the Sun won't kill the biosphere, the Earth will. As the mantle cools, the temperature contrast between the mantle and the core will no longer sustain core convection. Then Earth's magnetic field will power down. Without geo-dynamo shielding against galactic and solar radiation, bad things may happen: the rapid shutdown of Mars' dynamo is one hypothesis for the deterioration of Mars climate ~4 Gyr ago [4]. On the other hand, Earth's magnetic field strength decreased by a factor of 20 during the Laschamp Event ~41000 years ago [5], with no known effects on biology (or human culture). Diamond-anvil experiments are tough; few grad students make it past quals without breaking a diamond or two. The diamond-anvil technique is hitting diminishing returns, so modest advances are (rightly) celebrated. The same is true for deep-earth seismology and mantle geochemistry. A good new method is mapping the antineutrino flux from Earth. Antineutrinos are produced by radioactive decay and move in a straight line from source to surface. Mapping the Earth with geoneutrino observatories in the deep sea would help determine the power source for plate tectonics [6]. ---- [1] Garnero & McNamara: http://mcnamara.asu.edu/Publications/pdfs/Garnero_and_McNamara_Science_2008.pdf http://mcnamara.asu.edu/Publications/pdfs/Garnero_and_McNama... [2] Korenaga, "Urey Ratio and The Structure and Evolution of Earth's Mantle", http://people.earth.yale.edu/sites/default/files/korenaga08d.pdf http://people.earth.yale.edu/sites/default/files/korenaga08d... Korenaga is the best mid-career theorist actively working on this problem. [3] New result, from several teams working independently to analyze the Kepler dataset: Caltech http://arxiv.org/abs/1303.3013 http://arxiv.org/abs/1303.3013 (read this one first); Harvard team #1 http://arxiv.org/abs/1302.1647 http://arxiv.org/abs/1302.1647; Harvard team #2 http://arxiv.org/abs/1301.0842 http://arxiv.org/abs/1301.0842; Berkeley http://arxiv.org/abs/1304.0460 http://arxiv.org/abs/1304.0460. I'm assuming 0.1 stars per cubic parsec. [4] Lillis et al: http://seismo.berkeley.edu/~manga/lillisetal2008b.pdf http://seismo.berkeley.edu/~manga/lillisetal2008b.pdf. Later work broadly supports his conclusion that the dynamo died fast and early in Mars history. SETI Institute talk: https://www.youtube.com/watch?v=REiKzxWbzrQ https://www.youtube.com/watch?v=REiKzxWbzrQ It is not known whether loss of the magnetic field had a big or small effect on the Great Drying of Mars. Measuring modern atmosphere/water loss rates from modern Mars is the goal of the MAVEN mission, which launches this Nov - http://lasp.colorado.edu/home/maven/ http://lasp.colorado.edu/home/maven/ [5] Known from ice-core spikes in beryllium-10 (isotope produced by cosmic radiation hitting Earth's atmosphere) as well as magnetic paleo-intensity measurements in sediments. [6] http://www.phys.hawaii.edu/~sdye/hanohano.html http://www.phys.hawaii.edu/~sdye/hanohano.html. A knuckle is that SSBN reactors also emit neutrinos and neutrinos cannot be shielded, so deep-sea geoneutrino detectors could be strategically destabilizing. In practice either angular resolution or massive size would be needed to make deep-sea neutrino detectors useful to militaries.

54 points by groundCode 13y ago

tocomment 13y ago

It's a shame there's no good way to harness that.

ovis 13y ago
Although it's admittedly difficult when the higher temperatures are hundreds or thousands of kilometers away, geothermal power plants do in fact harness that.
- dkhenry 13y ago
  If I am not mistaken Iceland uses geothermal to a large extent and is very successful in doing so.
  - mtviewdave 13y ago
    Northern California, as well: http://en.wikipedia.org/wiki/The_Geysers http://en.wikipedia.org/wiki/The_Geysers
- comicjk 13y ago
  Yes, we could use more research in the technical side of that. Right now hard-rock drilling is so expensive that geothermal is only viable where natural circulation of underground water brings heat up from hotter regions.
blueprint 13y ago
It's important to note the fact that the heat in the core does not exist in isolation of other fields. The Earth is a dynamo system, and the energy in the core is connected to the planet's magnetic field, the energy bound up in its orbit around the sun, and its gravitational field.
3am 13y ago
Its rotation produces the magnetic field which keeps the solar wind from stripping away our atmosphere and leaving the Earth a dead planet like Mars. We're getting our money's worth.

aashaykumar92 13y ago

This article is fascinating but as someone who doesn't know much about this discipline, I'm hoping for someone to clarify my confusion: In the article, it states that our core has temperatures comprable to that of the sun. However, the sun is 93 million miles away while our core seems to only be approximately 4000 miles deep. Shouldn't the Earth be hotter than or are there just so many layers that the heat decreases at such a fast rate as it approaches the surface?

blueprint 13y ago
They're comparing the heat of Earth's core to the surface of the sun, not the core of the sun.
ovis 13y ago
The sun heats the earth surface through radiative heating, while the core is well insulated by the mantle and crust. Although they may have similar temperatures, the power output of the sun is certainly larger.
- jasallen 13y ago
  To provide some further context to ovis' (correct) statements, none of our 'heat', or other energy from the sun comes in the form of conduction. It comes in the form of radiation (light, et al) which the sun has in huge, massive, ginormous quantities. In pop culture, we often talk about the heat of the sun as if it's a direct indicator for the amount of power therein, and the amount of power output. But while it's quite hot, its also quite busy showering us with other forms of energy.
Jabbles 13y ago
I'm afraid there are many things wrong with your model of how heat works. However a simple factor is that the surface of the sun is ~10000 times larger than the surface of the earth.
monsterix 13y ago
> In the article, it states that our core has temperatures comprable to that of the sun. However, the sun is 93 million miles away while our core seems to only be approximately 4000 miles deep. I was thinking you were about to ask why in the universe are we not able to measure the temperature of earth core that's only 4000 miles away from us and yet we claim to know the temperature of something that 93 million miles away... :)

bttf 13y ago

Was anyone else led by the title of this post to contemplate the difference in heat between thought and the Earth's core?

bcbrown 13y ago

So the previous estimate was 5000 C, and now it's 6000C +/- 500C, and that's "far hotter"? That doesn't seem like a huge adjustment to me.

ecto 13y ago
Perhaps a ~17% change is not significant on the scale that we inhabit (20C today depending where you are), but 1000C is a lot of degrees.
- jlgreco 13y ago
  Indeed. It seems this new estimate puts it into "surface of the sun" territory (5700-8800K).
  - samstave 13y ago
    I know nothing about this, but I wonder if core temp would have any impact on the habitability of a planet. We know there is the habitable zone around a star, I wonder if that body in that zone would also need a certain core temp to support life.
    - jlgreco 13y ago
      I don't know much about this, but my understanding is that a hot core is not itself something that life particularly needs. The effects of that hot core however (Spinning core to make a magnetosphere? Volcanic activity changing atmospheric chemistry?) are probably more important. On the other hand, a hot core gives you deep sea thermal vents. Although I think the current prevailing theories don't have life originating near those on Earth, a hot core is certainly essential to life down there and, perhaps on another world, life could originate there.

edwinkite 13y ago

Geologist here. Earth's thermal evolution is unsolved decades after we figured out the stars. The Sun's temperature adjusts to energy production and loss on a 10^6 yr timescale (scaling as the time for a photon to diffuse from the heart of the Sun to the cold surface): << the Sun's age. The Earth's temperature adjusts to internal energy production and surface losses on a billion year timescale: of order the Earth's age. Planets have long memories and history matters. The Sun is reasonably well-mixed. Surface spectroscopy probes the make-up of the whole star. Earth is less well-stirred. Seismic imaging of the deep earth maps the edges of vast pods of material, radioactivity unknown, composition unknown (but definitely distinct from the near-surface stuff), age unconstrained but plausibly as old as the planet [1]. Structure and composition matter [2]. It's a hard problem. But it matters. When you look up at the night sky far from cities, for every star you see there's a habitable-zone Earth-radius planet that's closer [3]. We didn't know that six months ago. We think (for good, but circumstantial reasons) that complex life requires volcano-tectonic resurfacing - necessarily, a hot interior. Given that habitable-zone Earth-radius planets are not in short supply, the difference between fast and slow cooling for planets like Earth is the difference between a Galaxy where most every star system is habitable and one where almost all the planets are cinders. The core-mantle boundary heat flux Q_CMB estimated in this paper constrains the mantle energy balance d(E_mantle)/dt ~ Q_CMB - Q_surf + H_radioactive Surface heat flux Q_surf is ~46 terawatts. Mantle radioactivity H_radioactive is not well constrained but about 10 terawatts [2]. The implication is that despite the high core heat flux, Earth's mantle is cooling fast - maybe 100 microkelvins per century. Volcanism will therefore shut down in much less time than the remaining main sequence lifetime of the Sun. Absent human intervention, the reddening of the Sun won't kill the biosphere, the Earth will. As the mantle cools, the temperature contrast between the mantle and the core will no longer sustain core convection. Then Earth's magnetic field will power down. Without geo-dynamo shielding against galactic and solar radiation, bad things may happen: the rapid shutdown of Mars' dynamo is one hypothesis for the deterioration of Mars climate ~4 Gyr ago [4]. On the other hand, Earth's magnetic field strength decreased by a factor of 20 during the Laschamp Event ~41000 years ago [5], with no known effects on biology (or human culture). Diamond-anvil experiments are tough; few grad students make it past quals without breaking a diamond or two. The diamond-anvil technique is hitting diminishing returns, so modest advances are (rightly) celebrated. The same is true for deep-earth seismology and mantle geochemistry. A good new method is mapping the antineutrino flux from Earth. Antineutrinos are produced by radioactive decay and move in a straight line from source to surface. Mapping the Earth with geoneutrino observatories in the deep sea would help determine the power source for plate tectonics [6]. ---- [1] Garnero & McNamara: http://mcnamara.asu.edu/Publications/pdfs/Garnero_and_McNamara_Science_2008.pdf http://mcnamara.asu.edu/Publications/pdfs/Garnero_and_McNama... [2] Korenaga, "Urey Ratio and The Structure and Evolution of Earth's Mantle", http://people.earth.yale.edu/sites/default/files/korenaga08d.pdf http://people.earth.yale.edu/sites/default/files/korenaga08d... Korenaga is the best mid-career theorist actively working on this problem. [3] New result, from several teams working independently to analyze the Kepler dataset: Caltech http://arxiv.org/abs/1303.3013 http://arxiv.org/abs/1303.3013 (read this one first); Harvard team #1 http://arxiv.org/abs/1302.1647 http://arxiv.org/abs/1302.1647; Harvard team #2 http://arxiv.org/abs/1301.0842 http://arxiv.org/abs/1301.0842; Berkeley http://arxiv.org/abs/1304.0460 http://arxiv.org/abs/1304.0460. I'm assuming 0.1 stars per cubic parsec. [4] Lillis et al: http://seismo.berkeley.edu/~manga/lillisetal2008b.pdf http://seismo.berkeley.edu/~manga/lillisetal2008b.pdf. Later work broadly supports his conclusion that the dynamo died fast and early in Mars history. SETI Institute talk: https://www.youtube.com/watch?v=REiKzxWbzrQ https://www.youtube.com/watch?v=REiKzxWbzrQ It is not known whether loss of the magnetic field had a big or small effect on the Great Drying of Mars. Measuring modern atmosphere/water loss rates from modern Mars is the goal of the MAVEN mission, which launches this Nov - http://lasp.colorado.edu/home/maven/ http://lasp.colorado.edu/home/maven/ [5] Known from ice-core spikes in beryllium-10 (isotope produced by cosmic radiation hitting Earth's atmosphere) as well as magnetic paleo-intensity measurements in sediments. [6] http://www.phys.hawaii.edu/~sdye/hanohano.html http://www.phys.hawaii.edu/~sdye/hanohano.html. A knuckle is that SSBN reactors also emit neutrinos and neutrinos cannot be shielded, so deep-sea geoneutrino detectors could be strategically destabilizing. In practice either angular resolution or massive size would be needed to make deep-sea neutrino detectors useful to militaries.