New ideas for how Earth core formed

Liquid iron can percolate through rocks deep beneath our feet

Experiments on samples of iron and rock held at immense pressures have led to new ideas of how Earth's core formed.

Scientists from Stanford University have shown that iron metal will flow through rocks 1,000km beneath our feet.

Using sophisticated X-ray imaging, they watched molten metal moving through rocks, squeezed to huge pressures between the tips of pairs of diamonds.

Their results suggest that Earth's core did not form in a single step, but grew in a complicated sequence over time.

The depths of Earth are complex and multi-layered.

At the surface, the rocks forming the foundations of our cities, the stones that we build our lives upon, also provide the raw materials for society - metals, fuel, water and nutrients.

These are no more than a thin geological veneer on the planet. In many respects, the deep Earth remains as much of a mystery as Jupiter or Mars.

But new research in the journal Nature Geosciences gives new clues about how Earth may have taken shape and built its core.

A group of scientists, led by Stanford's Prof Wendy Mao, have shown how metallic iron may be squeezed out of rocky silicates more than 1,000km beneath the surface to form a metallic core.

Ceramic mantle
If you were to follow Jules Verne on a journey to the centre of the Earth, you would find a chemistry dominated by just three elements, until you got almost half the way to the centre - that's the first 3,000km of your journey.

Oxygen, silicon and magnesium (plus a little bit of iron) make up more than 90% of Earth's blanketing "ceramic" mantle.

Electrically and thermally insulating, the mantle is like a rock-wool blanket around the core. The minerals of the mantle are the stony part of the planet. But as you delve deeper on this "thought field trip", things suddenly and drastically change.

With more than half your journey ahead of you, you cross a boundary from the stony mantle into the metallic core. It is initially liquid in its upper stretches, and then solid right the way to the centre of the Earth.

The chemistry changes too, with iron forming almost all of the core, segregated into Earth's dense inner sphere.

The boundary between the metallic core and rocky mantle is a place of extremes. Physically, Earth's metallic liquid outer core is as different to the rocky mantle that overlies it as the seas are from the ocean floor here near Earth's surface.

One might (just about) imagine an inverted world of storms and currents of flowing red-hot metal in the molten outer core, pulsing through channels and inverted "ocean" floors at the base of the mantle.

The flowing of metal in the outer part of the core gives Earth its magnetic field, protects us from bombarding solar storms, and allows life to thrive.

How Earth's core came about has puzzled Earth Scientists for many years. Experiments on mixtures of silicate minerals and iron, cooked up in the laboratory, show that iron sits in tiny isolated lumps within the rock, remaining trapped and pinned at the junctions between the mineral grains.

- BBC.co.uk