During its infancy, meteorites constantly bombarded the forming planet, causing excessive amounts of frictional force. At the time, Earth was rife with volcanic activity. Since the beginning, the planet has cooled significantly. However, residual heat from the formation of Earth remains. Although the primordial heat has largely dissipated, another form of heat continues to warm the mantle and crust of the Earth. Naturally radioactive materials exist in large quantities deep in the Earth, with some residing around the crust.
During the natural decay process of the radioactive material, heat is released. What they do not know, however, is how much of the heat is primordial.
The issue is that if the Earth's heat is predominantly primordial, then it will cool off significantly quicker. However, if the heat is created mostly in part due to radioactive decay, then the Earth's heat will likely last much longer.
While that sounds pretty alarming, some estimates for the cooling of Earth's core see it taking tens of billions of years, or as much as 91 billion years. That is a very long time, and in fact, the Sun will likely burn out long before the core — in around 5 billion years. Earth's core keeps the temperature stable, but more importantly, it keeps the Earth's magnetic field in place.
This massive magnetic field extends into space and holds charged particles in place that are mostly collected from the solar winds. The fields create an impenetrable barrier in space that prevents the fastest, most energetic electrons from reaching Earth. The fields are known as the Van Allen belts, and they are what enables life to thrive on the surface of the Earth.
The collection of charged particles deflects and captures the solar wind preventing it from stripping the Earth of its atmosphere. Without it, our planet would be barren and lifeless. It is believed that Mars once had a Van Allen belt that protected it too from the Sun's deadly wind. However, once the core cooled, it lost its shield, and now it remains a desolate wasteland. The results, however, greatly differ making a final conclusion difficult to draw.
At the moment, it is unknown how much primordial and radioactive energy remains. When Earth coalesced from a homogenous rubble pile into its differentiated, layered state, its material separated by density. Buoyant material like water, air, and silicates stayed on top and in the middle, and dense material like iron sank to the center. This could be good news for the core paradox, however. The presence of lighter elements may propel convection in the core, giving the geodynamo a source of convection even if thermal convection is too weak.
If lighter elements cause convection, this source of buoyancy gives a work-around to the core paradox. Cohen, Hirose, and many others are investigating the effect of lighter elements on heat transport in the core. Novel follow-up studies are upping the ante as well.
Past studies have been conducted, for the most part, on solid samples. And so, when challenges like this are posed to the community, sometimes they are answered slowly because getting a good answer is difficult. But ultimately, they will be answered.
Duncombe, J. Published on 24 June Any reuse without express permission from the copyright owner is prohibited. Iddris et al. Skip to content In a thermal conductivity experiment, researchers shoot a green laser through a diamond anvil cell to heat an iron alloy sample. Metallurgy Lends a Hand But Hirose noticed that few people had measured the thermal conductivity of iron under extreme conditions, and the few studies that had been completed, using shock wave experiments, had large uncertainties and were not easily reproducible.
Not only do we not have the technology to "go to the core," but it is not at all clear how it will ever be possible to do so. As a result, scientists must infer the temperature in the earth's deep interior indirectly. Observing the speed at which of passage of seismic waves pass through the earth allows geophysicists to determine the density and stiffness of rocks at depths inaccessible to direct examination. If it is possible to match up those properties with the properties of known substances at elevated temperatures and pressures, it is possible in principle to infer what the environmental conditions must be deep in the earth.
The problem with this is that the conditions are so extreme at the earth's center that it is very difficult to perform any kind of laboratory experiment that faithfully simulates conditions in the earth's core. Nevertheless, geophysicists are constantly trying these experiments and improving on them, so that their results can be extrapolated to the earth's center, where the pressure is more than three million times atmospheric pressure.
The bottom line of these efforts is that there is a rather wide range of current estimates of the earth's core temperature. The "popular" estimates range from about 4, kelvins up to over 7, kelvins about 7, to 12, degrees F. If we knew the melting temperature of iron very precisely at high pressure, we could pin down the temperature of the Earth's core more precisely, because it is largely made up of molten iron.
But until our experiments at high temperature and pressure become more precise, uncertainty in this fundamental property of our planet will persist. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Discover World-Changing Science.
Read more from this special report: A Guide to Volcanoes. He provided some additional details on estimating the temperature of the earth's core: How do we know the temperature? Get smart. Sign up for our email newsletter.
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