Here's a few links, attesting to the recent activity in this field.
Enjoy!
http://www.physlink.com/News/121103PotassiumCore.cfm
Radioactive material may be primary heat source in Earth's core
Radioactive potassium, common enough on Earth to make potassium-rich bananas one of the "hottest" foods around, appears also to be a substantial source of heat in the Earth's core, according to recent experiments by University of California, Berkeley, geophysicists.
Radioactive potassium, uranium and thorium are thought to be the three main sources of heat in the Earth's interior, aside from that generated by the formation of the planet. Together, the heat keeps the mantle actively churning and the core generating a protective magnetic field.
But geophysicists have found much less potassium in the Earth's crust and mantle than would be expected based on the composition of rocky meteors that supposedly formed the Earth. If, as some have proposed, the missing potassium resides in the Earth's iron core, how did an element as light as potassium get there, especially since iron and potassium don't mix?
Kanani Lee, who recently earned her Ph.D. from UC Berkeley, and UC Berkeley professor of earth and planetary science Raymond Jeanloz have discovered a possible answer. They've shown that at the high pressures and temperatures in the Earth's interior, potassium can form an alloy with iron never before observed. During the planet's formation, this potassium-iron alloy could have sunk to the core, depleting potassium in the overlying mantle and crust and providing a radioactive potassium heat source in addition to that supplied by uranium and thorium in the core.
Lee created the new alloy by squeezing iron and potassium between the tips of two diamonds to temperatures and pressures characteristic of 600-700 kilometers below the surface - 2,500 degrees Celsius and nearly 4 million pounds per square inch, or a quarter of a million times atmospheric pressure.
"Our new findings indicate that the core may contain as much as 1,200 parts per million potassium -just over one tenth of one percent," Lee said. "This amount may seem small, and is comparable to the concentration of radioactive potassium naturally present in bananas. Combined over the entire mass of the Earth's core, however, it can be enough to provide one-fifth of the heat given off by the Earth."
Lee and Jeanloz will report their findings on Dec. 10, at the American Geophysical Union meeting in San Francisco, and in an article accepted for publication in Geophysical Research Letters.
"With one experiment, Lee and Jeanloz demonstrated that potassium may be an important heat source for the geodynamo, provided a way out of some troublesome aspects of the core's thermal evolution, and further demonstrated that modern computational mineral physics not only complements experimental work, but that it can provide guidance to fruitful experimental explorations," said Mark Bukowinski, professor of earth and planetary science at UC Berkeley, who predicted the unusual alloy in the mid-1970s.
Geophysicist Bruce Buffett of the University of Chicago cautions that more experiments need to be done to show that iron can actually pull potassium away from the silicate rocks that dominate in the Earth's mantle.
"They proved it would be possible to dissolve potassium into liquid iron," Buffet said. "Modelers need heat, so this is one source, because the radiogenic isotope of potassium can produce heat and that can help power convection in the core and drive the magnetic field. They proved it could go in. What's important is how much is pulled out of the silicate. There's still work to be done "
If a significant amount of potassium does reside in the Earth's core, this would clear up a lingering question - why the ratio of potassium to uranium in stony meteorites (chondrites), which presumably coalesced to form the Earth, is eight times greater than the observed ratio in the Earth's crust. Though some geologists have asserted that the missing potassium resides in the core, there was no mechanism by which it could have reached the core. Other elements like oxygen and carbon form compounds or alloys with iron and presumably were dragged down by iron as it sank to the core. But at normal temperature and pressure, potassium does not associate with iron.
Others have argued that the missing potassium boiled away during the early, molten stage of Earth's evolution.
The demonstration by Lee and Jeanloz that potassium can dissolve in iron to form an alloy provides an explanation for the missing potassium.
"Early in Earth's history, the interior temperature and pressure would not have been high enough to make this alloy," Lee said. "But as more and more meteorites piled on, the pressure and temperature would have increased to the point where this alloy could form."
The existence of this high-pressure alloy was predicted by Bukowinski in the mid-1970s. Using quantum mechanical arguments, he suggested that high pressure would squeeze potassium's lone outer electron into a lower shell, making the atom resemble iron and thus more likely to alloy with iron.
More recent quantum mechanical calculations using improved techniques, conducted with Gerd Steinle-Neumann at the Universität Bayreuth's Bayerisches Geoinstitüt, confirmed the new experimental measurements.
"This really replicates and verifies the earlier calculations 26 years ago and provides a physical explanation for our experimental results," Jeanloz said.
The Earth is thought to have formed from the collision of many rocky asteroids, perhaps hundreds of kilometers in diameter, in the early solar system. As the proto-Earth gradually bulked up, continuing asteroid collisions and gravitational collapse kept the planet molten. Heavier elements – in particular iron - would have sunk to the core in 10 to 100 million years' time, carrying with it other elements that bind to iron.
Gradually, however, the Earth would have cooled off and become a dead rocky globe with a cold iron ball at the core if not for the continued release of heat by the decay of radioactive elements like potassium-40, uranium-238 and thorium-232, which have half-lives of 1.25 billion, 4 billion and 14 billion years, respectively. About one in every thousand potassium atoms is radioactive.
The heat generated in the core turns the iron into a convecting dynamo that maintains a magnetic field strong enough to shield the planet from the solar wind. This heat leaks out into the mantle, causing convection in the rock that moves crustal plates and fuels volcanoes.
Balancing the heat generated in the core with the known concentrations of radiogenic isotopes has been difficult, however, and the missing potassium has been a big part of the problem. One researcher proposed earlier this year that sulfur could help potassium associate with iron and provide a means by which potassium could reach the core.
The experiment by Lee and Jeanloz shows that sulfur is not necessary. Lee combined pure iron and pure potassium in a diamond anvil cell and squeezed the small sample to 26 gigapascals of pressure while heating the sample with a laser above 2,500 Kelvin (4,000 degrees Fahrenheit), which is above the melting points of both potassium and iron. She conducted this experiment six times in the high-intensity X-ray beams of two different accelerators - Lawrence Berkeley National Laboratory's Advanced Light Source and the Stanford Synchrotron Radiation Laboratory - to obtain X-ray diffraction images of the samples' internal structure. The images confirmed that potassium and iron had mixed evenly to form an alloy, much as iron and carbon mix to form steel alloy.
In the theoretical magma ocean of a proto-Earth, the pressure at a depth of 400-1,000 kilometers (270-670 miles) would be between 15 and 35 gigapascals and the temperature would be 2,200-3,000 Kelvin, Jeanloz said.
"At these temperatures and pressures, the underlying physics changes and the electron density shifts, making potassium look more like iron," Jeanloz said. "At high pressure, the periodic table looks totally different."
"The work by Lee and Jeanloz provides the first proof that potassium is indeed miscible in iron at high pressures and, perhaps as significantly, it further vindicates the computational physics that underlies the original prediction," Bukowinski said. "If it can be further demonstrated that potassium would enter iron in significant amounts in the presence of silicate minerals, conditions representative of likely core formation processes, then potassium could provide the extra heat needed to explain why the Earth's inner core hasn't frozen to as large a size as the thermal history of the core suggests it should."
Jeanloz is excited by the fact that theoretical calculations are now not only explaining experimental findings at high pressure, but also predicting structures.
"We need theorists to identify interesting problems, not only check our results after the experiment," he said. "That's happening now. In the past half a dozen years, theorists have been making predictions that experimentalists are willing to spend a few years to demonstrate."
The work was funded by the National Science Foundation and the Department of Energy.
http://athene.as.arizona.edu/~lclose/teaching/images/lect8.html
Lecture 8
History of the Earth
Chapter 3
The dynamic Earth (Introduction to Geophysics)
Most geophysical processes stem from the transfer of heat from the Earth's core to its surface.
Why is the Earth's core hot?
1. The radio active decay of Uranium (U), Thorium (Th) and Potassium (K). Each radio active decay (the loss of some neutrons and protons) releases very little energy. However, all the countless events acting together release a large sustained amount of energy overtime. In the core of the Earth this energy is trapped and so the Earth's core is heated up.
2. As the solid inner grows latent heat is released as the molten outer core freezes to solid rock. Eventually the whole Earth will be solid and there will be no magnetic field.
3. Residual formation heat. Some of the kinetic energy (1/2mv2) of the impacting planetesimals would have been converted to heat. This residual formation heat helped melt the core initially.
4. Another early heat source was the heat produced as the heavy elements (like Iron (Fe) and Nickel (Ni)) "falling" into the core. This process also generated heat from friction.
The exchange of heat from the hot core to the cool surface is called convection (heat rises, cold sinks). In this manner the whole Earth has a series of big convective cells in its mantel. The result is a complex series of movements of the crust of the Earth as it "rides" on top of the convective cells below.
Plate Tectonics
In the 1950s and 60s geophysicists started to develop the concept of Plate Tectonics. Plate tectonics is the theory that describes the motion of the continental plates "riding" the tops of these massive convective cells in the Earth (like a conveyor belt).
Here is a movie showing how the plates have moved the continents
Today these plates move by about 10 cm/yr
• when these plates stick, and then suddenly slip, an Earthquake occurs
• when the heavier ocean crust sinks below the lighter (granite) continental crust (at subjection zones) there will be Earthquakes and Volcanos -the ring of fire around the Pacific is built this way. The Continental crust will also be crumpled, and as a result it is typical to see mountain ranges along the edges of these faults (for example the rocky mountains and the Andes).
• Seamount Island Chains -like the Hawaiian Islands- are made when one hot spot in the Earths mantle leads to continuous eruptions in the same spot. But as the crust moves along the ocean floor a chain of new islands appear.Sometimes (but not often) two continental plates collide. In this case neither plate is heavier and so they both "crumple". This is occurring today as the Indian plate collides with the Asian plate. The result of this collision is the Himalayas which are the highest mountains on Earth.Why is a hot core important for life on Earth?
1. the surface temperature is higher
2. active volcanism can out gas the atmosphere and oceans
3. volcanism is required to form land masses above the ocean
4. hot spots in the sea floor can be "safe" habitats for life
5. hot springs and even hot water deep in the Earth can harbor life
6. volcanoes play a role in the Earth's carbon cycle
Basin and Range
Tucson is located in a unique part of the world. The area where we live is called "Basin & Range" geography. This denotes that in Eastern California, Arizona, and New Mexico the terrain is dominated by short (often parallel) mountain ranges with large dry basins between them. This is a highly unusual land form caused by a unique event in the Earth's history.
• About 20 million years ago the continental plate of the Southwest became "attached" somehow to the pacific coast plate which was moving northwest at the time.
• Added to this was intense heat from magma close to the surface.
• The end result was the unique "Basin & Range disturbance" where the coast of California was pulled away from Arizona by some 38% of its original size.
• The hard cold rock on the top splintered into dozens of parallel ranges, while huge basins over 1 km deep were opened up between the rangeThe whole stretching event took a few million years. Then due to erosion the valleys filled in and the ranges wore down --further filling the valleys.
The reason Tucson exists today is because of the "fossil ground water" trapped in the huge 1 km deep valley basin exists below the city.
Radioactivity in Earth's core up for a look
vast uranium field serves as natural reactor
Keay Davidson, Chronicle Science Writer
Monday, November 29, 2004
Researchers are preparing to prove the discoveries of San Diego geologist, J. Marvin Herndon, who has found a huge, natural nuclear reactor or "georeactor" -- a vast deposit of uranium several miles wide -- at Earth's core, thousands of miles beneath our feet. Herndon and many others believe it explains otherwise puzzling phenomena of planetary science, such as fluctuations in the intensity of Earth's magnetic field. "Herndon's idea about (a reactor) located at the center of the Earth, has opened a new era in planetary physics," said four Russian scientists at Moscow's Institute for Nuclear Research and Kurchatov Institute in a Jan. 28 paper published online.
It might sound bizarre, the very idea of a "natural" nuclear reactor -- a geological version of commercial nuclear power plants such as Pacific Gas and Electric Co.'s Diablo Canyon plant near San Luis Obispo. The reactor at the Earth's core is just a much bigger and deeper version of an extinct natural nuclear reactor that scientists discovered in a uranium mine in Gabon, Africa, in 1972.
The Gabon reactor consists of geological deposits of uranium that, being radioactive, naturally emit subatomic particles called neutrons. These neutrons split the nuclei in adjacent uranium atoms, causing them to emit more neutrons and, thus, to split even more uranium atoms -- in effect, it's a slow-speed chain reaction. Research in the 1970s revealed that the Gabon reactor operated intermittently for a few million years about 2 billion years ago.
Scientists have long known the planet's core is divided into a solid and liquid part composed largely of iron, the liquid circulation of which powers Earth's magnetic field. They have not thought of the core as a repository for uranium, because uranium was not understood until 1945. Although the inevitability of uranium in the core was proposed in 1939 by scientist Walter Elsasser, on the basis that it is the heaviest naturally occurring element, so it would migrate to the core via gravity.
Herndon has demonstrated how a uranium georeactor in Earth's core explains reality better than older scientific ideas, by providing more convincing ways to:
-- Explain the ratios of helium isotopes emitted from volcanoes in Iceland and Hawaii. Those ratios are consistent with the ratios of helium isotopes emitted by a nuclear reactor.
-- Explain why planets such as Jupiter emit far more heat than they absorb from the sun. Herndon thinks they, too, have natural nuclear reactors at their cores. (Because heat is continually generated by the decay of radioactive elements in Earth's crust and mantle -- the regions above the core -- scientists are uncertain whether Earth emits more heat than it receives from the sun.)
-- Explain variations in the intensity of Earth's magnetic field, which fluctuates over time. Herndon has shown that in the core, the georeactor drives the motions of the liquid iron that creates the magnetic field. But the georeactor varies in activity levels over time. Those activity variations, he believes, might explain intensity variations in Earth's magnetic field.
Now, Rob de Meijer and associates at the Nuclear Physics Institute in Groningen, the Netherlands, are planning to demonstrate Herndon's proposals. They're drawing blueprints for a large device that could detect ghostly particles called antineutrinos that have escaped from Earth's core. When put into operation, it will capture antineutrinos that would fly through the roughly 4,000 miles of solid rock and emerge at the Earth's surface.
The European scientists have proposed drilling a shaft more than 1,000 feet deep into the island of Curacao in the Caribbean. They hope to lower into the shaft devices called photomultipliers, which could detect particles from the hypothetical deep-Earth georeactor.
The estimated cost: $80 million. In an e-mail to The Chronicle, de Meijer said he is seeking funding from the Dutch government and industrial consortiums. He and his team plan to visit Curacao in January to take the geological samples needed to design the subterranean antineutrino "antenna," as they call it.
Curacao is a good location for the antineutrino detector because "the island's rocks have relatively few natural radionuclides that could mask the (antineutrino) signal from the Earth's core," the journal Physics World noted in September. The detector could be confused by antineutrinos emitted by commercial nuclear reactors, but Curacao is far enough from the southeastern United States that reactors in Florida won't affect it.
"Dr. Herndon is a brilliant and original thinker. I agree with his proposal" said geoscientist David Deming of the University of Oklahoma.
"The problem with most scientists working today is that they have no knowledge of the history of science," Deming adds. "As late as 1955, continental drift was regarded as the equivalent of alien abductions, Bigfoot and the Loch Ness monster. By 1970, continental drift was an accepted part of the new theory of plate tectonics."
Richard Muller, a noted physicist and author at Lawrence Berkeley National Laboratory in Berkeley. Since the 1970s, Muller has done pioneering research in diverse fields, including cosmology and planetary sciences.
"Herndon's discovery is a very positive contribution to deep Earth science. He raises issues that are worth exploring at some length. " Muller adds. "I consider his work to be 'out of the box' thinking, and as such, it is valuable as a step forward in our understanding of reality."
On a side note, in case you're wondering: Unlike the planet-busting reactor of Superman lore, neither the Gabon reactor nor Herndon's hypothetical deep-Earth reactors could explode like atomic bombs. A-bombs require highly concentrated amounts of fissionable materials that are explosively compressed together in a fraction of a second -- far faster than the snail's-pace processes that would be characteristic of the natural reactors.
Herndon received his bachelor's degree in physics at UC San Diego in 1970. He studied nuclear chemistry and meteorites in graduate school at Texas A&M, where he received his doctoral degree for a thesis on meteorites. Operating as an independent scientist, over the years, he has published papers in prestigious journals, including the Proceedings of the National Academy of Sciences and the Proceedings of the Royal Society of London. His main allies are non-Americans, like the de Meijer team. On Dec. 16, Herndon is scheduled to deliver the prestigious annual "Christmas Lecture" at the European Commission's Institute for Transuranium Elements in Karlsruhe, Germany. It is felt that the huge antinuclear bias in American society is preventing other U.S. academics from getting on board, as they might lose tenure positions or funding by bucking the strong academic antinuke culture on this issue. Had his two sons -- now physicians -- planned to become scientists, he says, "I would have steered them away from it because you can't make a living and do legitimate science; you have to 'howl with the wolves' or you don't survive. This is a sad testament to our times. There's something very wrong in American science."
Herndon’s proposal
According to traditional theory, the core of Earth consists of iron. The SanDiego scientist J. Marvin Herndon has argued that a large deposit of uranium also exists in the core, where it powers a natural nuclear reactor or “georeactor.” Herndon believes the nuclear process is responsible for variations in the intensity of Earth’s magnetic field.
During the radioactive decays, the georeactor releases ghostly particles called antineutrinos, which fly through thousands of miles of solid rock to Earth’s surface. Scientists will test Herndon’s georeactor by using special instruments to detect the antineutrinos as they pass through the outer crust.
Sources: nuclearplanet.com; www.ansto.gov.au/edu/about/about_neutron.htm;
Other scientists have expanded Herndon's proposal to include Thorium and Potassium.
nasa
http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/11/29/MNGPIA17BL45.DTL
http://www.sciam.com/print_version.cfm?articleID=000B2C71-BCF0-1C71-9EB7809EC588F2D7
Why is the earth's core so hot? And how do scientists measure its temperature?
Jeff Atwell
Mount Vernon, Ohio
Quentin Williams, associate professor of earth sciences at the University of California at Santa Cruz offers this explanation:
There are three main sources of heat in the deep earth: (1) heat from when the planet formed and accreted, which has not yet been lost; (2) frictional heating, caused by denser core material sinking to the center of the planet; and (3) heat from the decay of radioactive elements.
It takes a rather long time for heat to move out of the earth. This occurs through both "convective" transport of heat within the earth's liquid outer core and solid mantle and slower "conductive" transport of heat through nonconvecting boundary layers, such as the earth's plates at the surface. As a result, much of the planet's primordial heat, from when the earth first accreted and developed its core, has been retained.
The amount of heat that can arise through simple accretionary processes, bringing small bodies together to form the proto-earth, is large: on the order of 10,000 kelvins (about 18,000 degrees Farhenheit). The crucial issue is how much of that energy was deposited into the growing earth and how much was reradiated into space. Indeed, the currently accepted idea for how the moon was formed involves the impact or accretion of a Mars-size object with or by the proto-earth. When two objects of this size collide, large amounts of heat are generated, of which quite a lot is retained. This single episode could have largely melted the outermost several thousand kilometers of the planet.
Additionally, descent of the dense iron-rich material that makes up the core of the planet to the center would produce heating on the order of 2,000 kelvins (about 3,000 degrees F). The magnitude of the third main source of heat--radioactive heating--is large, but quantitatively uncertain. The precise abundances of radioactive elements (primarily potassium, uranium and thorium) are is poorly known in the deep earth.
In sum, there was no shortage of heat in the early earth, and the planet's inability to cool off quickly results in the continued high temperatures of the Earth's interior. In effect, not only do the earth's plates act as a blanket on the interior, but not even convective heat transport in the solid mantle provides a particularly efficient mechanism for heat loss. The planet does lose some heat through the processes that drive plate tectonics, especially at mid-ocean ridges. For comparison, smaller bodies such as Mars and the Moon show little evidence for recent tectonic activity or volcanism.
We derive our primary estimate of the temperature of the deep earth from the melting behavior of iron at ultrahigh pressures. We know that the earth's core depths from 2,886 kilometers to the center at 6,371 kilometers (1,794 to 3,960 miles), is predominantly iron, with some contaminants. How? The speed of sound through the core (as measured from the velocity at which seismic waves travel across it) and the density of the core are quite similar to those seen in of iron at high pressures and temperatures, as measured in the laboratory. Iron is the only element that closely matches the seismic properties of the earth's core and is also sufficiently abundant present in sufficient abundance in the universe to make up the approximately 35 percent of the mass of the planet present in the core.
The earth's core is divided into two separate regions: the liquid outer core and the solid inner core, with the transition between the two lying at a depth of 5,156 kilometers (3,204 miles). Therefore, If we can measure the melting temperature of iron at the extreme pressure of the boundary between the inner and outer cores, then this lab temperature should reasonably closely approximate the real temperature at this liquid-solid interface. Scientists in mineral physics laboratories use lasers and high-pressure devices called diamond-anvil cells to re-create these hellish pressures and temperatures as closely as possible.
