by Raoul Girard
October 09, 2013

from FrenchTribune Website

 

 


Published lately in the journal Nature Geoscience, a study (Formation of an interconnected network of iron melt at Earth’s lower mantle conditions) conducted by researchers from School of Earth Sciences at Stanford University said that there are severe temperatures and pressures within the core of Earth.

Scientists have been looking for long for the actual processes occurring deep inside.

 

But, the conditions have allowed them discover just a bit addition regarding the core of Earth. In fact, the findings are being suspected to make theories of formation of the planet complex.

As per the findings, the innards of the planet are segregated into two layers. One is the rocky mantle comprised of silicates. On the other hand, there is a metallic core rich in iron. Scientists said that they were not able to untangle the mystery how the arrangement originally took place.

However, varied theories exist in relation to the evolution of Earth such as the rocks of Earth melted due to its hotness. But, some other studies said that Earth's temperature could not be so hot to melt silicates.

 

There was no base as yet to prove either case.

"Scientists had said that this theory wasn't possible, but now we're saying, under certain conditions that we know exist in the planet, it could happen", Wendy Mao was quoted as saying.



 

 

 

 

 



 Formation of...

An Interconnected Network of Iron Melt

...at Earth’s Lower Mantle Conditions
by Crystal Y. Shi,
Li Zhang,
Wenge Yang,
Yijin Liu,
Junyue Wang,
Yue Meng,
Joy C. Andrews
Wendy L. Mao
Nature Geoscience - 2013
doi:10.1038/ngeo1956
Received - 08 May 2013
Accepted - 23 August 2013
Published online - 06 October 2013

from Nature Website
 

 

Core formation represents the most significant differentiation event in Earth’s history.

 

Our planet’s present layered structure with a metallic core and an overlying mantle implies that there must be a mechanism to separate iron alloy from silicates in the initially accreted material. 1, 2

 

At upper mantle conditions, percolation has been ruled out as an efficient mechanism because of the tendency of molten iron to form isolated pockets at these pressures and temperatures. 3, 4, 5, 6

 

Here we present experimental evidence of a liquid iron alloy forming an interconnected melt network within a silicate perovskite matrix under pressure and temperature conditions of the Earth’s lower mantle.

 

Using nanoscale synchrotron X-ray computed tomography, we image a marked transition in the shape of the iron-rich melt in three-dimensional reconstructions of samples prepared at varying pressures and temperatures using a laser-heated diamond-anvil cell.

 

We find that, as the pressure increases from 25 to 64 GPa, the iron distribution changes from isolated pockets to an interconnected network. Our results indicate that percolation could be a viable mechanism of core formation at Earth’s lower mantle conditions.
 

 

 

At a glance
 

 


Figure 1:

3D distribution of iron alloy melt in silicate perovskite.
a–d, Samples were synthesized at 25 GPa (a), 39 GPa (b), 52 GPa (c) and 64 GPa (d).

The dimensions of each selected volume of interest are labelled.




Figure 2:

Regions of interest in the Fe-melt/silicate sample

prepared under different pressure–temperature conditions.





Figure 3:

Distribution of apparent dihedral angles for contacts between iron alloy melt and silicate perovskite.
a–d, Samples were synthesized at 25 GPa (a), 39 GPa (b), 52 GPa (c) and 64 GPa (d).

We report the median value of dihedral angles and the estimated errors based on the 95% confidence interval.




Figure 4:

3D renderings of the tomographic reconstruction of the iron alloy melt prepared at 64 GPa.
a, b, The channel in a at the Fe edge has been confirmed to be iron-rich material by element-sensitive TXM imaging;

the channels labeled in blue in b are contiguous as determined by using a 3D flood-fill algorithm. c,

The channel line set extracted from the reconstructed 3D volume;

the color map represents the relative thickness of the channel, with warmer colors indicating thicker channels.




Figure 5:

Schematic diagram showing possible Earth core formation mechanisms.
Magma ocean and percolation might be dominant mechanisms

over different pressure-temperature ranges during Earth’s core formation.

 

 

 

References

  1. Elsasser, W. M. in Earth Science and Meteorites (eds Geiss, J. & Goldberg, E.) 1–30 (North Holland, 1963).

  2. Stevenson, D. J. in Origin of the Earth (eds Newsom, H. E. & Jones, J. H.) 231–249 (Oxford Univ. Press, 1990).

  3. Shannon, M. C. & Agee, C. B. High pressure constraints on percolative core formation. Geophys. Res. Lett. 23, 2717–2720 (1996).

  4. Rubie, D. C., Melosh, H. J., Reid, J. E., Liebske, C. & Righter, K. Mechanisms of metal-silicate equilibration in the terrestrial magma ocean. Earth Planet. Sci. Lett. 205, 239–255 (2003).

  5. Shannon, M. C. & Agee, C. B. Percolation of core melts at lower mantle conditions. Science 280, 1059–1061 (1998).

  6. Terasaki, H., Frost, D. J., Rubie, D. C. & Langenhorst, F. Percolative core formation in planetesimals. Earth Planet. Sci. Lett. 273, 132–137 (2008).