BEIJING, May 6 (Xinhuanet) -- A new model put forth
in the May 2 issue of the journal Science, suggests inner Earth is more complex
than a simple core, mantle, crust explanation.
Earth is made up of several layers, once thought to
be pretty distinct.
The skin, or crust, goes down about 25 miles (40 km).
Below that is the mantle area, which extends about halfway to the center of the
planet. The mantle is a thick layer of silicate rock surrounding a dense,
iron-nickel core, and it is subdivided into the upper and lower mantle,
extending to a depth of about 1,800 miles (2,900 km). The outer core is beneath
that and extends to 3,200 miles (5,150 km) and the inner core to about 4,000
miles (6,400 km).
New data reveal the mantle consists of more varying
material than was thought. So convection ¡ª how heated material bubbles up ¡ª is
now thought to work differently.
"Imagine a pot of water boiling," explains researcher
Allen McNamara of Arizona State University. "That would be all one kind of
composition. Now dump a jar of honey into that pot of water. The honey would be
convecting on its own inside the water and that's a much more complicated
system."
One clue to the new thinking is that seismic waves
traveling through the planet have long been measured to travel at inexplicably
different speeds. Sharp speed changes suggest differing materials. On each side
of the planet there are two big, chemically distinct, dense piles or blobs of
material that are hundreds of kilometers thick ¨C one beneath the Pacific and the
other below the Atlantic and Africa, the researchers say.
"You can picture these piles like peanut butter,"
McNamara said. "It is solid rock, but rock under very high pressures and
temperatures becomes soft like peanut butter, so any stresses will cause it to
flow."
How stuff moves within the piles should help
scientists better understand how surface plates move around, causing earthquakes
and building mountains.
"The piles dictate how the convective cycles happen,
how the currents circulate," McNamara said. "If you don't have piles then
convection will be completely different."
(Agencies)
