Science and Environment

Scientists say they have gained new insight into what lies
at the very centre of the Earth.

Research from China and the US suggests that the
innermost core of our planet has another, distinct region at
its centre.
The team believes that the structure of the iron crystals
there is different from those found in the outer part of the
inner core.
The findings are reported in the journal Nature
Geoscience .
Without being able to drill into the heart of the Earth, its
make-up is something of a mystery.
So instead, scientists use echoes generated by earthquakes
to study the core, by analysing how they change as they
travel through the different layers of our planet.
Prof Xiaodong Song, from the University of Illinois at
Urbana-Champaign said: "The waves are bouncing back and
forth from one side of the Earth to the other side of the
Earth."
Prof Song and his colleagues in China say this data
suggests that the Earth's inner core - a solid region that is
about the size of the Moon - is made up of two parts.
The scientists believe the Earth's inner core is composed
of two parts
The seismic wave data suggests that crystals in the "inner
inner core" are aligned in an east-to-west direction - flipped
on their side, if you are looking down at our planet from
high above the North Pole.
Those in the "outer inner core" are lined up north to south,
so vertical if peering down from the same lofty vantage
point.
Prof Song said: "The fact we are discovering different
structures at different regions of the inner core can tell us
something about the very long history of the Earth."
The core, which lies more than 5,000km down, started to
solidify about a billion years ago - and it continues to grow
about 0.5mm each year.
The finding that it has crystals with a different alignment,
suggests that they formed under different conditions and
that our planet may have undergone a dramatic change
during this period.
Commenting on the research, Prof Simon Redfern from the
University of Cambridge said: "Probing deeper into the solid
inner core is like tracing it back in time, to the beginnings of
its formation.
"People have noticed differences in the way seismic waves
travel through the outer parts of the inner core and its
innermost reaches before, but never before have they
suggested that the alignment of crystalline iron that makes
up this region is completely askew compared to the
outermost parts.
"If this is true, it would imply that something very substantial
happened to flip the orientation of the core to turn the
alignment of crystals in the inner core north-south as is seen
today in its outer parts."
He added that other studies suggest that the Earth's
magnetic field may have undergone a change about half a
billion years ago, switching between the equatorial axes and
the polar axis.
"It could be that the strange alignment Prof Song sees in
the innermost core explains the strange palaeomagnetic
signatures from ancient rocks that may have been present
near the equator half a billion years ago," he added.
"For the moment, however, the model proposed in this
paper needs testing against other ways of analysing the
seismic properties of Earth's innermost core, since no other
researchers have previously considered evidence for the
same conclusions in their studies."