By Andy Soos – Jul 21, 2011, 8:04 AM CDT
Earth’s inner core is the innermost geologic layer of planet Earth. It is primarily a solid ball with a radius of about 1,220 km (760 mi), which is about 20% of Earth’s radius or 70% of the Moon‘s radius.[1][2]
There are no samples of Earth’s core accessible for direct measurement,
as there are for Earth’s mantle.[3]
Information about Earth’s core mostly comes from analysis of seismic waves
and Earth’s magnetic field.[4]
The inner core is believed to be composed of an iron–nickel alloy with some other elements. The temperature at the inner core’s surface is estimated to be approximately 5,700 K (5,430 °C; 9,800 °F), which is about the temperature at the surface of the Sun.[5] Source Earth’s inner core – Wikipedia
What spreads the sea floors and moves the continents? What melts iron in the outer
core and enables the Earth’s magnetic field. Heat. Geologists have used temperature measurements from more than 20,000 boreholes around the world to estimate that some 44 terawatts (44 trillion watts) of heat continually flow from Earth’s interior into space. Where does it come from? Initially the earth heated up using energy released by gravitational collapse, and while this energy completely melted the planet,
this heat would have all been lost by now as the Earth is 4.6 billion years old.
However, the earth is still hot in its core as we can see from all the volcanic activity on
our planet. The energy which keeps the core hot and the volcanoes active is produced by radioactive decay. Heavy, radioactive elements such as uranium sank to the Earth’s core along with the Iron and Nickel early in Earth’s history (when it was all molten) and these radioactive elements have been heating the core (rather like a nuclear power station) ever since.
In 2005 scientists in the KamLAND collaboration, based in Japan, first showed that
there was a way to measure the heat contribution directly. The trick was to catch what KamLAND dubbed geoneutrinos — more precisely, geo-antineutrinos — emitted when radioactive isotopes decay.
Anti-neutrinos are made in the beta-decay of neutron-rich daughter fragments in the fission process. A neutrino meaning “small neutral one”, is an elementary particle that usually travels close to the speed of light, is electrically neutral, and is able to pass through ordinary matter almost unaffected. This makes neutrinos extremely difficult to detect. Neutrinos have a very small, but nonzero mass. Neutrinos are similar to the more familiar electron, with one crucial difference: neutrinos do not carry electric charge.
KamLAND scientists have now published new figures for heat energy from radioactive decay in the journal Nature Geoscience. Based on the improved sensitivity of the KamLAND detector, plus several years’ worth of additional data, the new estimate is not merely consistent with the predictions of accepted geophysical models but is precise enough to aid in refining those models.
All models of the inner Earth depend on indirect evidence. Leading models of the
kind known as bulk silicate Earth (BSE) assume that the mantle and crust contain only lithophiles (rock-loving elements) and the core contains only siderophiles (elements that like to be with iron). Thus, all the heat from radioactive decay comes from the crust and mantle — about eight terawatts from uranium 238 (238U), another eight terawatts from thorium 232 (232Th), and four terawatts from potassium 40 (40K).
This is more heat energy than the most popular earth core model suggests, but still far
less than the Earth’s total. Says Freedman (One of the authors), “One thing we can say with near certainty is that radioactive decay alone is not enough to account for Earth’s
heat energy. Whether the rest is primordial heat or comes from some other source is
an unanswered question.” Other sources — primordial heat left over from the planet’s formation, and possibly others as well — must account for the rest.
Better models are likely to result when many more geoneutrino detectors are located in different places around the globe, including midocean islands where the crust is thin and local concentrations of radioactivity (not to mention nuclear reactors) are at a minimum.
Electricity From Earth’s Core
A Texas engineer who designs power stations has an idea for clean, safe, free energy:
Bury power-generating tubes deep in the Earth’s crust and tap the energy of the planet’s molten core. By Erik Baard.
A RADICAL NEW method of producing electricity from the
Earth’s inner heat has been devised by a power plant designer from Texas.
Doyle Brewington of ESOR Consulting Engineers in Houston has designed a long,
self-contained turbine shaft called a Power Tube that could tap subterranean heat
without relying on geysers and steam vents.
“I spent 25 years building power plants and I saw the damage they were causing,” Brewington said. “The noxious gas being emitted by a lot of these steam turbines
we’re causing a lot of acid rain around the world.”
Brewington’s Power Tube is a sealed tube, four-foot wide and 185-feet long, containing a vapor-driven generator. The idea is to bury the Power Tube deep enough to touch hot rock.
The tip of the Power Tube contains a pair of hydrocarbons, isopentane and isobutene, that turn to vapor when in contact with rock that’s at least 220 degrees Fahrenheit (104 C).
The vapor rises to drive a generator above. The vapor is then cooled back into a liquid by helium that is compressed and expanded using sound waves.
The liquefied hydrocarbons are then pumped back to the tip to restart the cycle in an unbroken loop. Magnetic suspension, rather than lubrication, eliminates friction in the turbine.
Brewington has designed a half-size prototype that is just over two feet in diameter and 85 feet long. It is expected to produce a megawatt of electricity, enough to power 750 homes. The first Power Tubes to go into operation will be in Hawaii and Costa Rica, Brewington said. He is still talking to authorities and didn’t say when it would go into the ground.
Brewington said full-size Power Tubes will produce 10 MW, enough to light up a small residential town. Unlike old-fashioned geothermal sites, which consume up to 10 acres
of land, Power Tubes will have only a small maintenance shed on top.
And because Power Tubes run silently, homes and offices could be built over them.
Working Power Tubes will be easy to assemble on site: long ones will be transported in sections, Brewington said. And on-site maintenance of a Power Tube would be swifter than that for traditional power plants because the entire shaft can be removed and replaced in hours. The defective tube could then be retrofitted back at the plant.
If Brewington is correct, much of the energy needed for expanding industrialization
could be provided without releasing greenhouse gases associated with burning fossil fuel or the risks associated with nuclear energy.
Many of the fastest growing economies sit on the Earth’s “Ring of Fire,” a circuit of volcanoes, earthquakes, and other manifestations of tectonic tension.
Brewington claims that 48 countries in the Ring of Fire alone could be powered entirely by Power Tubes, a great stride over other geothermal systems. “Anything that’s got magma underneath it is great,” he said. But leading researchers are watching with a wary eye, and some have expressed strong reservations about Brewington’s plans.
They don’t see how he’s going to pull off his power plans without water.
Probing Question: What heats the earth’s core?
By Joe Anuta
The Earth’s Plasmasphere (nasa.gov)
Although we crust-dwellers walk on nice cool ground, underneath our feet the Earth is
a pretty hot place. Enough heat emanates from the planet’s interior to make 200 cups of piping hot coffee per hour for each of Earth’s 6.2 billion inhabitants, says Chris Marone, Penn State professor of geosciences. At the very center, it is believed temperatures exceed 11,000 degrees Fahrenheit, hotter than the surface of the sun.
A cross-section of the Earth reveals three concentric layers. Around the outside, a thin, hard crust ranging from 10 to 100 kilometers thick. Under that, a donut-shaped mantle 2,900 kilometers thick. Instead of dough, it consists of viscous molten rock that flows
very slowly, on a geological time scale. “It moves about as fast as your fingernails grow,” Marone explains. At the center of the Earth lies a two-part core. “The inner part is about the size of our moon,” Marone says, “and has a density of essentially steel.”
The outer core surrounding it is an ocean of liquid metal 2,300 kilometers thick.
The Earth’s rotation makes this ocean flow and swirl, and the moving metal generates
the planet’s magnetic field.
Most of Earth’s heat is stored in the mantle, Marone says, and there are four sources that keep it hot. First, there’s the heat left over from when gravity first condensed a planet from the cloud of hot gases and particles in pre-Earth space. Also, as the molten ball cooled, some 4 billion years ago, the outside hardened and formed a crust. The mantle is still cooling down.
“We don’t think this original heat is a major part of the Earth’s heat, though,”
Marone says. It only contributes 5 to 10 percent of the total, “about the same amount as gravitational heat.”
To explain gravitational heat, Marone again evokes the image of the hot, freshly formed Earth, which was not of a consistent density. In a gravitational sorting process called differentiation, the denser, heavier parts were drawn to the center, and the less dense areas were displaced outwards. The friction created by this process generated considerable heat, which, like the original heat, still has not fully dissipated.
Then there’s latent heat, Marone says. This type arises from the core’s expanding as the Earth cools from the inside out. Just as freezing water turns to ice, that liquid metal is turning solid—and adding volume in the process. “The inner core is becoming larger by about a centimeter every thousand years,” Marone says. The heat released by this expansion is seeping into the mantle.
For all this, however, Marone says, the vast majority of the heat in Earth’s interior—up to 90 percent—is fueled by the decaying of radioactive isotopes like Potassium 40, Uranium 238, 235, and Thorium 232 contained within the mantle. These isotopes radiate heat as they shed excess energy and move toward stability. “The amount of heat caused by this radiation is almost the same as the total heat measured emanating from the Earth.”
Radioactivity is present not only in the mantle, but in the rocks of Earth’s crust.
For example, Marone explains, a 1-kilogram block of granite on the surface emanates
a tiny but measurable amount of heat (about as much as a .000000001-watt light bulb) through radioactive decay. That may not seem like much. But considering the vastness of the mantle, it adds up, Marone says. Sometime billions of years in the future, he predicts, the core and mantle could cool and solidify enough to meet the crust.
If that happens, Earth will become a cold, dead planet like the moon. Long before such
an occurrence, however, the Sun will likely have evolved into a red-giant star and grown large enough to engulf our fair planet. At that point, whatever heat is left in the mantle
will hardly matter. Chris Marone, Ph.D., is a professor of geosciences at Penn State.
Marone can be reached at cjm38@psu.edu.
A New Study Just Revealed That Earth’s Core Is Actually Leaking
ByHANIKA RIZO, DAVID MURPHY & DENIS ANDRAULT, THE CONVERSATION
NATURE 11 July 2019
Mt Bromo crater. – Bing video
Earth’s magnetic field protects and makes our planet habitable by stopping harmful high-energy particles from space, including from the Sun. The source of this magnetic field is the core at the centre of our planet. But the core is very difficult to study, partly because
it starts at a depth of about 2,900 kilometres (1,800 miles), making it too deep to sample and directly investigate.
Yet we are part of a research team that found a way to get information about Earth’s core, with details published recently in Geochemical Perspective Letters.
It’s hot down there
The core is the hottest part of our planet with the outer core reaching temperatures of more than 5,000 degrees Celsius (9,000 Fahrenheit). This has to affect the overlying mantle and it is estimated that 50 percent of volcanic heat comes from the core.
Volcanic activity is the planet’s main cooling mechanism. – Search (bing.com)
Let’s Dig More Volcanoes To Cool The Earth’s Surface.
Certain volcanism, such as that which is still forming volcanic islands of Hawaii and Iceland, might be linked to the core by mantle plumes that transfer heat from the core
to Earth’s surface. Yet whether there is any exchange of physical material between the
core and the mantle have been a subject of debate for decades.
Our findings suggest some core material does transfer into the base of these mantle plumes, and the core has been leaking this material for the past 2.5 billion years.
We discovered this by looking at very small variations in the ratio of isotopes of the element tungsten (isotopes are basically versions of the same element that just contain different numbers of neutrons).
To study Earth’s core.
We need to search for chemical tracers of core material in volcanic rocks derived from
the deep mantle. We know the core has a very distinct chemistry, dominated by iron and nickel together with elements such as tungsten, platinum and gold that dissolve in iron-nickel alloy. Therefore, the metal alloy-loving elements are a good choice to investigate
for traces of the core.
Core leak | Structure of the earth, Earth, Earth layers (pinterest.com)
Tungsten (chemical symbol W) as the base element has 74 protons.
Tungsten has several isotopes, including 182W (with 108 neutrons) and 184W
(With 110 neutrons). These isotopes of tungsten have potential to be the most conclusive tracers of core material, because the mantle is expected to have much higher 182W/184W ratios than the core. This is because of another element, Hafnium (Hf), which does not dissolve in iron-nickel alloy and is enriched in the mantle and had a now-extinct isotope (182Hf) that decayed to 182W.
This gives the mantle extra 182W relative to the tungsten in the core.
But the analysis required to detect variations in tungsten isotopes is incredibly challenging, as we are looking at variations in the 182W/184W ratio in parts per million and the concentration of tungsten in rocks is as low as tens of parts per billion.
Fewer than five laboratories in the world can do this type of analysis.
Evidence of a leak
Our study shows a substantial change in the 182W/184W ratio of the mantle over Earth’s lifetime. Earth’s oldest rocks have significantly higher 182W/184W than most rocks of the modern-day Earth.
The change in the 182W/184W ratio of the mantle indicates that tungsten from the core has been leaking into the mantle for a long time. Interestingly, in Earth’s oldest volcanic rocks, over a time frame of 1.8 billion years there is no significant change in the mantle’s tungsten isotopes.
This indicates that from 4.3 billion to 2.7 billion years ago, little or no material from
the core was transferred into the upper mantle. But in the subsequent 2.5 billion years,
the tungsten isotope composition of the mantle has significantly changed.
We infer that a change in plate tectonics, towards the end of the Archean Eon from about 2.6 billion years ago triggered large enough convective currents in the mantle to change the tungsten isotopes of all modern rocks.
Why the leak?
If mantle plumes are ascending from the core-mantle boundary to the surface, it follows that material from Earth’s surface must also descend into the deep mantle. Subduction, the term used for rocks from Earth’s surface descending into the mantle, takes oxygen-rich material from the surface into the deep mantle as an integral component of plate tectonics.
Experiments show that increase in oxygen concentration at the core-mantle boundary could cause tungsten to separate out of the core and into the mantle.
Alternatively, inner core solidification would also increase the oxygen concentration
of the outer core. In this case, our new results could tell us something also about the
evolution of the core, including the origin of Earth’s magnetic field.
How the Earth’s core might be leaking material into the mantle plumes. (Neil Bennett)
Earth’s core started as entirely liquid metal and has been cooling and partially solidifying over time. The magnetic field is generated by the spin of the inner solid core. The time of inner core crystallisation is one of the most difficult questions to answer in Earth and planetary sciences.
Our study gives us a tracer that can be used to investigate core-mantle interaction and the change in the internal dynamics of our planet, and which can boost our understanding of how and when the magnetic field was turned on.
Hanika Rizo, Assistant Professor, Carleton University; David Murphy, Lecturer in Geoscience, Queensland University of Technology, and Denis Andrault, Professor, Université Clermont Auvergne.
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