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.
Earth's core far hotter than thought
21–28 of 28 posts
Re: Earth's core far hotter than thought
#22This 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…
The temperatures you're comparing are between the core of the earth and the radiation temperature of the surface of the sun. It's way hotter in the sun's core (20 million Kelvin IRRC)
Re: Earth's core far hotter than thought
#23So 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.
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.
Re: Earth's core far hotter than thought
#24So 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.
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.
Indeed. It seems this new estimate puts it into "surface of the sun" territory (5700-8800K).
Re: Earth's core far hotter than thought
#25Earlier quoted context omitted.
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.
Indeed. It seems this new estimate puts it into "surface of the sun" territory (5700-8800K).
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.
Re: Earth's core far hotter than thought
#26Earlier quoted context omitted.
Indeed. It seems this new estimate puts it into "surface of the sun" territory (5700-8800K).
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.
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.
Re: Earth's core far hotter than thought
#27Earlier quoted context omitted.
A lot of the radiation that the sun's core emits gets through its surface without interacting with it much. You can infer that from http://en.wikipedia.org/wiki/Sun : Temperature: - Center (modeled): 1.57×10^7 K[1] - Photosphere (effective): 5,778 K[1] - Corona: ~5×10^6 K => The sun's surface is about its coolest part. Its core is about 3000 times as hot. That's where the solar heat comes from.
A lot of the radiation that the sun's core emits gets through its surface without interacting with it much. This is false. The sun is very opaque; photons from the core could take millions of years to reach the surface. https://en.wikipedia.org/wiki/Radiation_zone https://en.wikipedia.org/wiki/Solar_core#Energy_transfer This is the article you're looking for: https://en.wikipedia.org/wiki/Corona#Coronal_heating_probl…
> photons from the core could take millions of years to reach the surface.
And it would be most unlikely they'd be the same photons that started on the journey. Likely they'd be absorbed and different photons re-emitted many times.
Re: Earth's core far hotter than thought
#28Geologist 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): 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_McNama...
[2] Korenaga, "Urey Ratio and The Structure and Evolution of Earth's Mantle", 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 (read this one first); Harvard team #1 http://arxiv.org/abs/1302.1647; Harvard team #2 http://arxiv.org/abs/1301.0842; Berkeley 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. 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 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/
[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. 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.