* Astronomy

The deepest hole humans have ever dug reaches 12 kilometres below the ground of Russia's Kola Peninsula. Although we now have a spacecraft on its way to Pluto - about six billion kilometres away from the sun - we still cannot send a probe into the deep earth. For practical purposes, then, the centre of the planet, which lies 6,380 kilometres below us, is farther away than the edge of our solar system. In fact, Pluto was discovered in 1930, and the existence of the earth's inner core was not established - using seismological data - until six years later.
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Earth's mantle flows fast

The Earth's mantle flows far more rapidly around a sinking tectonic plate than previously thought, according to new computer modelling by UC Davis geologists. The findings could change the way that we think about plate tectonics and the amount of energy available for earthquakes. The results will be published May 20 in the journal Nature.

"Our model suggests that some parts of the mantle are moving at screaming speeds compared to what we can observe directly at the Earth's surface. There is much more mixing and more rapid transport of heat in these regions of the Earth than we suspected" - Magali Billen, associate professor of geology at UC Davis and co-author of the paper.

Billen and graduate student Margarete Jadamec, now a postdoctoral researcher at Monash University in Australia, studied the Alaskan subduction zone, where the Pacific plate is diving beneath Alaska and pushing up Mt. McKinley.
To do so, they built the most detailed computer model to date of the plate and the surrounding mantle. The model revealed that rather than moving at roughly the same speed as the plate, the mantle was flowing much faster.

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Clues point to 'density trap' in early mantle

When Earth was young, it exhaled the atmosphere. During a period of intense volcanic activity, lava carried light elements from the planet's molten interior and released them into the sky. However, some light elements got trapped inside the planet. In this week's issue of Nature, a Rice University-based team of scientists is offering a new answer to a longstanding mystery: What caused Earth to hold its last breath?
For some time, scientists have known that a large cache of light elements like helium and argon still reside inside the planet. This has perplexed scientists because such elements tend to escape into the atmosphere during volcanism. However, because these elements are depleted in the Earth's upper mantle, Earth scientists are fairly certain the retained elements lie in a deeper portion of the mantle. Researchers have struggled to explain why some gases would be retained while others would rise and escape into the air. The dominant view has been that the lowermost mantle has been largely isolated from the upper mantle and therefore retains its primordial composition.
In the new study, a team of researchers from Rice, the University of Michigan and the University of California-Berkeley suggests that a particular set of geophysical conditions that existed about 3.5 billion years ago -- when Earth's interior was much warmer -- led to the formation of a "density trap" about 400 kilometres below the planet's surface. In the trap, a precise combination of heat and pressure led to a geophysical rarity, an area where liquids were denser than solids.
Today, liquids generated in the mantle are less dense than solids and therefore rise to the surface to form volcanoes. However, several billion years ago, a hotter mantle permitted deeper melting and generated dense liquids that stalled, crystallized and eventually sank to the bottom of the mantle.

Source Rice University

-- Edited by Blobrana on Thursday 18th of February 2010 02:35:02 PM

A University of Arkansas professor and his colleagues have shown that the Earth's mantle contains the same isotopic signatures from magnesium as meteorites do, suggesting that the planet formed from meteoritic material. This resolves a long-standing debate in the field over the planet's origins.
Fangzhen Teng, assistant professor of geosciences at the University of Arkansas, and Wei Yang and Hong-Fu Zhang of the Chinese Academy of Sciences report their findings in Earth and Planetary Science Letters.
The researchers examined magnesium isotopes in chondrites - meteorites containing elements formed from the condensation of hot gases in the solar system. They also looked at samples from different depths in the Earth's mantle. Isotopes have the same chemical properties, but different weights, so some processes cause what looks like the same material to behave differently. The different proportions of isotopes within a rock can tell scientists something about the original source of the material.

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