 |
|
Earth's core rotates faster than its crust, scientists say
August 26, 2005CHAMPAIGN, Ill. - Scientists have ended a 9-year-old debate by proving that Earth's core rotates faster than its surface, by about 0.3 to 0.5 degree per year.
"Extraordinary claims require extraordinary proof," said Xiaodong Song, a professor of geology at the University of Illinois at Urbana-Champaign and corresponding author of a paper to appear in the Aug. 26 issue of the journal Science. "We believe we have that proof."
Earth's iron core consists of a solid inner core about 2,400 kilometers in diameter and a fluid outer core about 7,000 kilometers in diameter. The inner core plays an important role in the geodynamo that generates Earth's magnetic field, and an electromagnetic torque from the geodynamo is thought to drive the inner core to rotate relative to the mantle and crust.
The first observational evidence for differential rotation was presented in 1996 by Song and Paul Richards, a seismologist at the Lamont-Doherty Earth Observatory of Columbia University. For the past nine years, some seismologists have suspected that flaws, or artifacts, in the data were responsible for the purported movement.
By comparing historical seismic waves traversing Earth's fluid and solid cores, Song and his colleagues found compelling evidence for differential rotation of the solid inner core. The researchers reported observations of 17 sets of similar seismic waves - called waveform doublets - from earthquakes occurring in the South Sandwich Islands region off the coast of South America.
The doublets, which were recorded at up to 58 seismic stations in and near Alaska with a time separation of up to 35 years, allowed the researchers to detect temporal changes along the sampling paths.
"The similar seismic waves that passed through the inner core show systematic changes in travel times and wave shapes when the two events of the doublet are separated in time by several years," Song said. "The only plausible explanation is a motion of the inner core."
The most likely explanation for why the inner core is rotating at a different speed, Song said, is electromagnetic coupling. "The magnetic field generated in the outer core diffuses into the inner core, where it generates an electric current. The interaction of that electric current with the magnetic field causes the inner core to spin, like the armature in an electric motor."
The fluid outer core decouples the solid inner core's movement from the mantle. Because the fluid outer core is not very viscous, frictional drag is small.
"Differential rotation is a fundamental dynamic process that goes to the heart of the origin of our planet and how it has evolved," Song said. "There is still much to learn about the inner Earth."
University of Illinois at Urbana-Champaign
The first observational evidence for differential rotation was presented in 1996 by Song and Paul Richards, a seismologist at the Lamont-Doherty Earth Observatory of Columbia University. For the past nine years, some seismologists have suspected that flaws, or artifacts, in the data were responsible for the purported movement.
By comparing historical seismic waves traversing Earth's fluid and solid cores, Song and his colleagues found compelling evidence for differential rotation of the solid inner core. The researchers reported observations of 17 sets of similar seismic waves - called waveform doublets - from earthquakes occurring in the South Sandwich Islands region off the coast of South America.
The doublets, which were recorded at up to 58 seismic stations in and near Alaska with a time separation of up to 35 years, allowed the researchers to detect temporal changes along the sampling paths.
"The similar seismic waves that passed through the inner core show systematic changes in travel times and wave shapes when the two events of the doublet are separated in time by several years," Song said. "The only plausible explanation is a motion of the inner core."
The most likely explanation for why the inner core is rotating at a different speed, Song said, is electromagnetic coupling. "The magnetic field generated in the outer core diffuses into the inner core, where it generates an electric current. The interaction of that electric current with the magnetic field causes the inner core to spin, like the armature in an electric motor."
The fluid outer core decouples the solid inner core's movement from the mantle. Because the fluid outer core is not very viscous, frictional drag is small.
"Differential rotation is a fundamental dynamic process that goes to the heart of the origin of our planet and how it has evolved," Song said. "There is still much to learn about the inner Earth."
University of Illinois at Urbana-Champaign
Earth's Core is a Recycling Product
The planets of the solar system, including the Earth, formed about four and a half billion years ago from a swirling disk of gas and dust that was left over from the newly formed Sun. However, we do not understand, why the Earth ended up being different from other Earth-like or «terrestrial» planets and how the earliest features, like the metallic core, developed. Research at ETH Zurich by Professor Alex Halliday, to be published in this week's edition of Nature, claims to have found some answers. It has generally been assumed that the Earth's metallic core, which generates the magnetic field, formed by segregating dense metallic iron from the accumulated mixture of metal and silicate
No Core In Volcanoes
A hot debate in the Earth Sciences is finally resolved in this week's issue of Nature. Researchers from the Department of Earth Sciences at Bristol University show that large volcanoes do not contain material from the Earth's core. This overturns previous theories that conflicted with models of how the Earth's magnetic field is sustained. The magnetic field results from the movement of liquid iron in the core and affects everything from bird migration to the navigation of aircraft, so it is crucial to understand how it has been sustained over geological time. Large volcanoes, like those on Hawaii, form in response to the up-welling of hot, molten lava in so-called 'plumes'. These plumes hav
More Earths Core Current Events and Earths Core News Articles
 | Tarzan at the Earth's Core by Edgar Rice Burroughs |
 | At the Earth's Core (Pellucidar Series) by Edgar Rice Burroughs When the inventor Perry fires up his burrowing prospector, it runs out of control, plunging him with his young protege into the centre of the earth. There, instead of being destroyed by the molten lava they expect to find, they discover an inner world of bizarre savagery and unearthly beauty. Here mighty dinosaurs still roam alongside beasts never seen in the world above. And to their horror,... |
 | At the Earth's Core by Edgar, Rice Burroughs The aborigine, apparently uninjured, climbed quickly into the skiff, and seizing the spear with me helped to hold off the infuriated creature. Blood from the wounded reptile was now crimsoning the waters about us and soon from the weakening struggles it became evident that I had inflicted a death wound upon it. Presently its efforts to reach us ceased entirely, and with a few convulsive movements... |
 | At the Earth's Core by Edgar Rice Burroughs When Abner Perry invents a vehicle that essentially drills through the earth, he takes it to his good friend (and independently wealthy man about town) David Ennis. And what else can they do? Drill down into the earth, of course. What they find there isn't what we'd expect: it's an inner world called Pellicidar, a place where the sun neither sets nor rises -- because what appears to be the sun is... |
 | Tarzan At the Earth's Core (Ace SF Classic, F-180) by Edgar Rice Burroughs |
| Tarzan At the Earth's Core by Edgar Rice Burroughs | |
 | Tarzan at the Earth's Core (Bison Frontiers of Imagination) by Edgar Rice Burroughs Continuing the saga of Pellucidar, the empire located in the Earth's hollow center, Tarzan at the Earth's Core is the fourth work in this classic series. The American explorer and emperor of Pellucidar, David Innes, has been captured by the deadly Korsar pirates. Picking up on the desperate cries for help emanating from Pellucidar, Jason Gridley of Tarzana brings the message to the only person... |
 | Tarzan 2-in-1 (Tarzan at the Earth's Core/Tarzan the Invincible) (Tarzan , No 13&14) by Edgar Rice Burroughs TARZAN AT THE EARTH'S COREA startling radio transmission summoned Tarzan to the savage land of Pellucidar, hidden deep inside the Earth. His challenge? Rescue a kidnapped emperor. But first he was forced to emerge victorious over titanic pterodactyls, fierce snake men, and other demonic creatures who hungered to destroy him.TARZAN THE INVINCIBLEWhen Tarzan tried to stop some greedy tyrants in... |
 | Sociology: A Down-to-Earth Approach, Core Concepts (3rd Edition) (MySocLab Series) by James M. Henslin Adapted from Henslin's best-selling comprehensive text, Core Concepts provides in-depth coverage of ten high-priority topics that are the foundation of many introductory sociology courses. This unique paperback offers a concise and economical format without sacrificing depth of coverage. Unlike a "brief" or "essentials" text, the ten chapters that make up Core Concepts are not edited down from a... |
 | At the Earth's Core (Ace SF Classic, F-156) by Edgar Rice Burroughs The First paperback edition. With the title, Ace began (FINALLY!) to systematically reprint the novels of Burroughs in mass market paperback form. With the fabulous Krenkel cover art, it is a classic among... |
| © 2008 BrightSurf.com |