While most
of us take the ground under our feet for granted, Earth's past is written
within its intricate layers, just like the pages of a novel. This is the story
of our lives.
Researchers
have discovered new evidence for a whole new chapter of Earth's history:
Earth's inner core appears to contain a second, much more inner core.
According
to Joanne Stephenson of Australia, we've all been told that the Earth has four
primary layers: the crust, the mantle, the outer core, and the inner core.
What we
know about what lies under the Earth's crust is largely based on what volcanoes
have revealed and seismic waves have whispered. Scientists also determined that
the scorching hot inner center, with temperatures exceeding 5,000 degrees
Celsius (9,000 degrees Fahrenheit), makes up just 1% of Earth's total volume
based on these indirect observations.
Now,
Stephenson and colleagues have discovered new evidence that the Earth's inner
core can be divided into two layers.
It's very
exciting - and it can necessitate rewriting textbooks! She continued.
The
researchers used a search algorithm to sift through thousands of inner core
models and compare them to data gathered by the International Seismological
Centre over decades on how long seismic waves take to travel through Earth.
![]() |
Differences in the paths of seismic waves as they travel across the Earth's layers. (Journal of Geophysical Research: Solid Earth, 2021, Stephenson et al.) |
So, what's
going on down there? The researchers looked at various models of the inner
core's anisotropy, or how variations in the make-up of its material affect
seismic wave properties, and discovered that some were more likely than others.
Although
some models claim that the inner core's material channels seismic waves faster
parallel to the equator, others argue that the combination of materials allows
for faster waves parallel to the rotational axis of the Earth. Even then, there
are disagreements about the precise degree of difference at different angles.
The inner
core did not display much difference with depth, but there was a shift in the
slow direction to a 54 degree angle, with the faster direction of waves running
parallel to the axis, according to this analysis.
According
to Stephenson, we discovered evidence of a change in the composition of
iron, which suggests two separate cooling events in Earth's history.
The
specifics of this major occurrence remain a mystery, but we've gained another
piece of the puzzle in our understanding of the Earth's inner heart.
These new
results may explain why some experimental evidence has been incongruent with current
Earth structure models.
For quite
some time, the existence of an innermost layer has been suspected, with
suggestions that the iron crystals that make up the inner core have different
structural alignments.
The team
wrote in their paper that the distribution of global earthquakes and receivers
limits them, particularly at the polar antipodes, and that the missing data
reduces the certainty of their conclusions. However, their findings are
consistent with other recent research on the anisotropy of the innermost inner
heart.
A new
method in progress could soon fill in some of these data gaps, allowing
scientists to confirm or refute their findings and, possibly, translate more
stories written in this early layer of Earth's history.
0 Comments